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GOVESMWEi^ FUuLiCATIONS
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UNIVERSITY OF CONNtCTlCUT
■A I
FOR Rrrrr
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DEPARTMENT OF THE INTERIOR
MONOGKAPHS
United States Geological Survey
VOLUME XXXIII
WASHINGTON
GOVERNMENT FEINTING OFFICE
1899
CONTENTS,
Page.
Letter of transmittal xv
Preface xvii
Part I. — General geology of the Naruagansett Basik, by N. S. Shaler.
Chapter I. — Position and surface relations of the Narragausett Basin, and the roclis it contains. 7
General features 7
Stratigraphical and orogenic relations 10
Results of the action of orogenic forces 20
Overthrust phenomena 25
Dike rocks of the hasin 27
Chapter II. — Physical history of the hasin 30
Relation to marine and atmospheric erosion and deposition 30
Age of Carhoniferous rocks of tlie basin 36
Original relation of the Narragansett Basin to the sea 37
Original distribution of the east Appalachian coal field 38
Ancient margin of the basin 40
Relative erosion of east and west Appalachians 40
Recent changes of level 46
General statement concerning base-leveling 47
Cycles of deposition , 49
Arkose deposits of the basin 50
Relation of arkoses to erosion 55
Record value of conglomerates 59
Red color of the Cambrian and the Carboniferous 62
Chapter III. — Glacial liistory of the Narragausett Basin 64
Carboniferous conglomerates 64
Last Glacial period 67
Amount of erosion 71
Chapter IV. — Economic resources of the basin 77
Soils 77
Coals 79
Condition of the beds 80
Characteristics of the coals 82
Conditions of future economic work 85
Iron ores: Iron Hill deposit 88
Part II. — Geology of the northern and eastern portions of the Narragansett Basin.
BY J. B. Woodworth.
Chapter i. — The jiroblem of stratigraphic succession 99
Repetition of lithological characters 100
Transition of lithological characters 100
Effects of igneous intrusions 101
Metamorphism 101
Folding and faulting 101
Denudation 101
y
VI CONTENTS.
Pakt II — Continued.
Chapter I. — The problem of stratigraphic succession — Coutinuetl. Page.
Glaciatiou 102
Suljraergeuce 103
Absence of artificial excavations 103
Ch.ipter II. — The pre-Carbonlferous rocks 104
Algoulvlan period 101
Blackstone series 101
Cumberland quartzltes 106
Ashton schists 107
Smlthfield limestones 107
Cambrian period 109
Lower Cambrian 109
Middle Cambrian (unrepresented) 109
Upper Cambrian - 109
Silurian period (unrepresented) --- 113
Chert pebbles - 113
Chapter III. — The Igneous rocks of the border of the basin 114
Granitic rooks 114
Plympton felsltes 116
Granite-porphyry 117
Other rocks 117
Gabbro hills of Sharon 118
Chapter IV. — The Carboniferous basin 119
General structure of the basin 121
Maps of the boundary of the basin 124
Boundary of the basin on the north and east 125
From Cranston to the Blackstone Elver 125
From Bl.ackstone River to SheldonvUIe 127
Connection between the Narragausett and Norfolk County basins 127
Sheklonville cross fault 127
From Sheldonville to Foolish Hill 127
Foolish Hill fault 128
From Foolish Hill to Brockton 128
From Brockton to North River 129
Shumatuscacant fault 129
From North River to Lakeville 129
From Lakeville to Steep Brook 130
Inliers 130
North Attleboro inller 131
Nemasket granitlte area 131
Summary 131
Chapter A'. — The Carboniferous strata 133
Determination of horizons within the basin 133
Means of determining superposition ..." 133
Tabular view of the strata in the Narragausett Basin 134
Formations below the Coal Measures 135
Pondville group 135
Basal arkose beds 135
Foolish Hill exposures 135
North Attleboro exposures 135
Pierces Pasture in Pondville, Norfolk County Basin 135
Absence of basal granitic conglomerates 136
Geographical conditions indicated by the basal arkose 137
Absence of Iron oxides In the basal arkose 138
Absence of carbonaceous matter .along northern margin 139
Extent of arkose zoue 139
CONTENTW. VII
Part II — Contiuued.
Chapter V.— The Carboniferous strata— Continued.
Formatious below the Coal Measures— Continued.
Pondville group — Continued. I'^ige-
Suprabasal conglomerates 1*''
Millers River conglomerate I'i"
South Attleboro exposure ^"^^
Jenks Park exposure in Pawtucket I'll
Wamsutta group
Bed rock areas
Area along the northern border 1*''
Gray sandstones of the northern border Hi
North Attleboro area ^-^^
Conglomerates 1"*^
Sandstones ■*■* '
Shales
147
Central Falls area ^^'^
Pawtucket area
Red beds in Attleboro, Rehoboth, and Norton liS
Norfolk County area ^*°
South Attleboro limestone bed 1^9
Attleboro sandstone _^
Igneous associates of the Wamsutta group 152
Diabase ^l^
Onnrtz-nornhvrv aroup '■°^
155
Diamond Hill quartz mass
Wamsutta volcanoes ' ^^"^
Folding of the Wamsutta group 1='^
Flora of the Wamsutta group 1^8
Coal Measures
Cranston beds -
162
Providence area
Pawtucket shales
163
ouuii-ainjo^*.- u ot*iJiMou<jjjv,ij- .----.-•---- ---- ---- ----
East Side area iu Providence ^^^
Teumile Riverbeds
AiCUaUOll l»±ixii3 v:7.vjj0SUre -- -• -...
East Providence area
-tax
Leonards Corner quarries '■^•^
Section from Watchemooket Cove to Riverside 16o
Halsey Farm section at Silver Spring 166
Exposures in Seekonk
Hunts Mills section 1^^
Perrins anticline
Bored well near Lebanon Mills 1^^
Seekonk beds -
Seekonk conglomerate '_
Beds north of the Tenmile River in Attleboro 1^^
Contact of red and gray beds, with local unconformity 17b
Red shales
Raindrop imprints
Attleboro syncline
Blake Hill fault block ^°"
Fossils ^g2
Coal "
Blake Hill thrust plane ^°^
Dighton conglomerate group
VIII CO:i>fTENTS.
Part II — Continued.
Chapter V. — The Carboniferous strata— Continued. Page.
Extension of the Coal Measures north and east of Taunton 187
Dedham quadrangle 187
Mansfield area 188
Flora of Mansfield section 191
Bridgewater area 192
Abington quadrangle 193
Taunton quadrangle 195
Red beds 195
Outcrops in Norton 195
Winnecounet ledges 196
Scolithus beds 197
Taunton waterworks section 198
AVestville section 199
Taunton River Valley 200
Middleboro quadrangle 200
Chapter VI. — Organic geology 202
Insect fauna 202
Stratigraphic position of the fauna 203
Odontopteris flora 203
List of plants identified by Lesquereux 204
Coal beds 205
Search for coal 207
Thickness of the Carboniferous 208
Acknowledgments 211
Appendix. — Bibliography of the Cambrian and Carboniferous rocks of the Narragansett Basin. 212
Part III. — Geology of the Carboniferous strat.a. of the southwestern portion of
THE NaRRAGANSETT BaSIN, VilTH AN ACCOUNT OF THE CAMBRIAN DEPOSITS, BY
Aug. F. Foerste.
Chapter I. — Introduction 223
Difficulties of the field 223
Arrangement of report 225
Chapter II. — The western islands of the bay 227
Dutch Island 227
Conanicut Island 228
Fox Hill, Beaver Head 228
Northern half of the island, north of Round Swamp 229
Southern half of the island, soiith of Round Swamp 232
Shale region 232
Granite area, the Dumplings, and the arkose region west of the Dumplings 233
Hope Island 235
Prudence Island 237
Chapter III.— The western shore of the bay 242
From Saunderstown to Narragansett Pier 242
Along the shore 242
West of the cove and Pattaquamscott River 246
From Saunderstown to AVickford 248
From Wickford to East Greenwich 251
AVestern border of the Carboniferous basin, from East Greenwich to Natick and northward
into Cranston 252
Rocks east of the westernborderof the Carboniferous area in Warwick and southern Cranston. 256
Warwick Neck 258
Chapter IV. — The northern shore of the bay 259
Providence River and eastward 259
RumstickNeck 260
CONTENTS. IX
Part III — Continued.
Chapter IV. — The northern shore of the bay — Continued. Page.
Popasquash Neoli 261
Bristol Neclv 261
Carboniferous area 261
Granite area 262
Warren Necli 264
Conglomerates and shales of S wansea and Warren, north of the necks 264
Gardeners Neck 267
Braytons Point and northward 268
Sewammock Neck 268
Chapter Y. — The eastern shore of the bay 269
Steep Brook 269
FallEiver 270
TownsendHill 270
Tiverton 271
Gould Island 272
Granite area at the northeast end of Aquidneck Island 273
Eastern border of the Carboniferous basin south of Tiverton Four Corners 274
Sandstone series between Windmill Hill and the cove north of Browns Point 275
Coarse conglomerate series along the east shore of Sakonnet River 278
High Hill Point 278
Fogland Point 278
Exposures west of Nonquit Pond 279
Exposures between Tiverton Four Corners and the northeast side of Naunaquacket Pond . 280
Little Compton shales 281
Chapter VI. — Aquidneck, or the Island of Rhode Island, with the islands of Newport Harbor. . . 284
Arkose and pre-Carboniferous rocks on Sachuest Neck 284
Arkose 281
Pre-Carboniferous rocks 286
Eastern shore of Aquidneck Island as far south as the second cove northwest of Black
Point 288
Coarse conglomerates and underlying sandstone series from Black Point to the north end
of Smiths Beach 290
Coarse conglomerates and underlying rocks on the neck at Eastous Point 294
Paradise coarse conglomerates 295
Paradise Rocks 295
The Hanging Rocks 298
Pre-Carboniferous area 300
Isolated conglomerate exposures near Eastons Pond and northward 303
Miautonomy Hill and Coasters Harbor Island conglomerates 304
Miantonomy Hill 304
Beacon Hill 304
Field exposures of coarse conglomerates 304
Coddington Neck 305
Bishop Rock 305
Coasters Harbor Island 306
Newport Harbor Islands 307
Gull Rocks 307
Rose Island 308
Conanicut Island 308
Line of separation between Carboniferous and pre-Carboniferous rocks 308
Goat Island and Little Lime Rock 309
Fort Greene 309
Morton Park and southward 309
Northeast lines of possible faulting 310
Carboniferous rocks along the Newport Cliffs 310
X CONTENTS.
Part III — Continued.
Chapter VI. — Aquidueok, or the Island of Rhode Island, etc. — Continued. Page.
Newport Neck and southern cliff rocks 314
Greenish igneous rock in the cliffs southwest of Sheep Point 314
Granite area at the south end of the cliffs 315
Granite area on eastern Newport Neck 316
Greenish and purplish argillitic rock of middle Newport Neck 316
Pre-Carboniferous green and purple shales of western Newport Neck 316
Shale series from Coddlngton Cove to Lawtons A'' alley 319
Greenish-blue shales of Slate Hill and southward 320
Shale series north of Lawtons Valley 320
Shore exposures north of Coggeshall Point 320
Portsmouth mine and northeastward 321
Line of exposures three-eighths of a mile west of the Newport road 326
Shale series at Butts Hill 327
Green shales and conglomerates of the northern syncline 327
Green shales along the western Newport road 327
Conglomerates 328
Relations to Slate Hill shales 329
Chapter VII.— The Kingstown series 331
Unity and lithological character of the Kingstown sandstone series 331
Section from the Bonnet to Boston Neck 333
Section from the Bonnet to Hazard's quarry and Indian Corner 333
Kingstown series in southwestern Cranston and western Warwick 334
Probable thickness of the Kingstown sandstone series in Cranston and Warwick ... 336
Warwick Neck exposures 336
Exposures on the western islands of the bay 337
Thickness of strata between the Bonnet and Dutch Island 337
Lithology of the Dutch Island series 338
Beaver Head section 338
Total thickness of the Kingstown series, including the conglomerate at Beaver
Head 338
Western shore of Conanicut 339'
Eastern shore of Conanicut 339
Probable folding in the northern part of Conanicut Island 340
Hope Island 341
Kingstown series exposures on the western islands 342
Prudence Island 342
Western Bristol Neck 343
Eumstick Neck 344
Kingstown sandstones equivalent to lower part of Coal Measures group 344
Triangular area of the Kingstown series in the Narragansett Basin, narrowing
southward 344
Thickness of the series and evidence of folding 345
Rocky Point conglomerate and its connection with the estimate of the thickness of
the northern section 346
Chief features of the Kingstown series 346
Fossil-plant localities 347
Chapter VIII. — The Aquidneck shales 348
Area occupied by the Aquidneck shale series 348
Southern Conanicut 349
Prudence Island 350
Thickness of shale series on each side of the Prudence Island syncline 351
Bristol Neck 351
Aquidneck Island 352
Thickness of the shale section east of the Portsmouth syncline 353
conte:sts. XI
Part III — Continued.
Chapter VIII.— The Acxnidneck shales — Continued. Page.
Probable thickness of the shale section west of the Portsmouth syncline 353
Lithological variations in the shale series 354
Geological structure of the middle third of Aquidneck Island 354
Strata probably folded 355
Gould Island of the Middle Passage 356
Southern third of Aqiiidneek Island 356
Upper green shales of the Aquidneck series 356
Sakounet sandstones of the Aquidneck series west of the river 357
Thickness of the uiiper green shales 357
Thickue.ss of the Sakounet sandstones 358
Northern extension of the Aquidneck shales 358
Equivalents of the Kingstown sandstone and Aquidneck shale series northeast of Warren
Neck 358
Sakonnet sandstones on the east side of the river 359
Absence of the shale series beneath the coarse conglomerates east of the Sakonnet River. .. 360
Wedge-shaped areal distribution of the Aquidneck shale series 361
Equivalence of the Kingstown sandstones and the Aquidneck shales 361
Fossils of the Aquidneck shale series 363
Chapter IX. — The Purgatory conglomerate 364
Coarse conglomerate overlying the Aquidneck shale series 364
Sakonnet sandstones within the Aquidneck shales, in transition to the coarse con-
glomerate 365
Coarse conglomerate forming the latest Carboniferous rocks in the southern part of
the Narragansett Basin 365
Purgatory conglomerate as a typical exposure 365
Identity of the Purgatory and the Sakonnet Eiver western shore coarse conglom-
erate 366
Possible syncline between the two western Paradise ridges of conglomerate 366
Hanging Rock ridge, possibly the eastern side of an anticlinal fold 367
Dips immediately east of Hanging Rock ridge 367
Interpretation adopted 367
Southward pitch of the great Paradise-Hanging Rook syncline 368
Southward pitch of the Sakonnet River syncline 369
Western coarse conglomerate exposures 369
Possible syncline immediately west of Miantonomy Hill 369
Possibility of two horizons of conglomerate at Miantonomy Hill 370
Interpretation adopted 371
Geological position of the Newport Cliff section 371
Portsmouth synclinal conglomerate 373
Conglomerates of Warwick Neck and Swansea 373
Thickness of the coarse conglomerate 373
Fossil localities 374
Chapter X. — The arkoses and basal conglomerates 375
Natiok arkose 375
From Natick to Cranston 375
Base of the Carboniferous south of Natick 376
Probable relations between the various granites and pegmatites and the Carbon-
iferous beds 376
Tiverton arkose 378
From Steep Brook to Nannaquacket Pond 378
South of Nannaquacket Pond 379
Equivalence of the Tiverton arkoses to those near Natick 379
Sachuest arkose '. 379
Conanicut arkose 380
Rose Island and Coasters Harbor Island arkose 380
XII
CONTENTS.
Part III— Continued. ^^S^-
Chapter XI.— The pre-Carboniferous rocks of the southwestern portion of the Narragansett Basin 381
Little Coniptou and Newport Neck shales 383
Quartzitesof Natick - ^^^
Chapter XII.— The Cambrian strata of the Attleboro district 386
Cambrian brook localities - ^^^
Localities 1 and 2, southwest of North Attleboro 388
Valley of locality 3 392
Locality 4, northeast of Diamond Hill - 393
Maps and sections
Index -
394
395
ILLUSTRATIONS.
Plate I. Landscape looking -svestward across the upper portion of Narragansett Bay, in the
lowland of the Carboniferous area, to the base-leveled area of mainly crystalline
and pre-Carbonlferous rocks 7
II. Pre-Carboniferous rocks at western border, near Providence, Rhode Island 126
III. Plant-bearing outcrop of Wamsutta group in North Attleboro, Massachusetts 146
IV. Faulted diabase dikes in North Attleboro, Massachusetts 152
V. Rocky Hill, Providence, Rhode Island, a glaciated ridge of the Carboniferous 162
VI. Carboniferous sandstones at Silver Spring, Rhode Island 166
VII. Carboniferous sandstones near Attleboro, Massachusetts 176
VIII. Medium-sized conglomerate, Attleboro, Massachusetts 176
IX. Ripple-marked vertical sandstones, Attleboro, Massachusetts 178
X. Raindrop Imprints on vertical strata, Attleboro, Massachusetts 178
XI. Plainville Valley, Wrenthani, Massachusetts 180
XII. Vertical bed of Dighton conglomerate at Attleboro, Massachusetts 184
XIII. Near view of Dighton conglomerate, Attleboro, Massachusetts 184
XIV. Selected waterworn and indented pebbles from Dighton conglomerate, Attleboro,
Massachusetts Igg
XV. Vertical Carboniferous sandstones, Plainville, Massachusetts 186
XVI. General view of surface at AVest Mansfield, Massachusetts 188
XVII. Geological map of the northern and eastern portions of the Narragansett Basin 210
XVIII. Contact of pegmatites with Kingstown shales, Watsons Pier, Rhode Island 242
XIX. Coarse pegmatites of Watsons Pier, Rhode Island 244
XX. Cross-stratification in pebbly sandstone of Kingstown series. Devils Foot Ledge, Rhode
Island 248
XXI. Sandstone-gneiss of Kingstown series. Devils Foot Ledge, Rhode Island 334
XXII. Stratification and slaty cleavage, Aquidneck shales, eastern shore of Prudence Island.. 350
XXIII. Wave-cut bench in Aquidneck shales, western shore of Prudence Island 352
XXIV. Fretwork weathering of Aquidueclv shales, Prudence Island 362
XXV. Pegmatite dikes cutting Kingstown shales, Watsons Pier, Rhode Island 376
XXVI. Hoppiu Hill, a granite mass surrounded by Cambrian, North Attleboro, Massachusetts. 384
XXVII. Sketch map of the North Attleboro Cambrisin localities 386
XXVIII. Sections in the Narragansett Bay region 394
XXIX. Sections in the Narragansett Bay region 394
XXX. Sections in the Narragansett Bay region 394
XXXI. Geological map of the southern part of the Narragansett Basin 394
Fig. 1. Diagram of assumed conditions of compressive strain in rocks in a basin of accumu-
lation 49
2. Theoretical plan of the great folds of the Narragansett Basin 27
3. Diagram showing misleading synclinal exposures of similar strata 102
4. Exposure of disconnected dike in Lime Rock quarries, Rhode Island 108
5. Sketch map of distribution of upper Cambrian pebbles 410
6. Map showing distribution of metamorphosed Carboniferous rocks 120
XIII
XIV ILLUSTRATIONS.
Page.
Fig. 7. Map showing general outline of the Narragansett Basin 121
8. Section across eastern arm of the basin 122
9. Outline map and general cross section of the northern part of the basin 123
10. Edward Hitchcock's cross section of the Carboniferous area 123
11. Map showing distribution of red sediments 142
12. Geological section northward from Robinson Hill 145
13. Diagram showing disapjiearance of the Wamsutta group in the Coal Measures 148
14. Section through felsite knob in Attleboro, Massachusetts 153
15. Geological section in the Millers River region 156
16. Geological section in the Arnolds Mills region 157
17. Hypothetical geological section cast and west through Providence, Rhode Island 160
18. Folded and faulted Carboniferous shales at Pawtucket, Rhode Island 162
19. Sketch of zone of excessively jointed sandstones, face of McCormick's quarry 166
20. Geological section from Watchemocket Cove to Riverside, Rhode Island 166
21. Geological section through rocky islets at Halsey Farm, Silver Spring, Rhode Island. .. 167
22. Geological section of rocky headland near Silver Spring, Rhode Island 168
23. Theoretical section of folded structure on western margin of the Narragansett Basin.. 169
24. Contemporaneous erosion with unconformity in the Carboniferous at Attleboro,
Massachusetts 176
25. Diagram showing cross bedding 178
26. Geological section of Plain ville Valley and thrust plane 183
27. Section of the Mansfield Coal Measures 190
28. ■ Geological section in Westville, Massachusetts 199
29. Diagram illustrating the case where boring affords a satisfactory test for coal Ijeds 208
30. Diagram illustrating the case where trenching affords a satisfactory test for coal 208
LETTER OF TRANSMITTAL,
Department of the Interior,
United States Geological Survey,
Cambridge, Massachusetts, March 2, 1896.
Sir: I have the honor to submit herewith, for pubhcation, a report on
the geology of the Nan-agansett Basin. This report contains the result of
a considerable amount of work done by me or undei my direction since I
became an officer of the Survey. In part, however, it is the result of
studies undertaken before that connection was established. The object of
the report is to set forth the results so far attained in the study of a field
which presents singular difficulties in the way of its interpretation, and
which will require the observation of many other students before it becomes
thoroiTghly well known. Since the preparation of the report was under-
taken I have been ordered to extend the results of a general nature there
attained to other similar basins on the Atlantic coast. On this account
it has seemed desirable to postpone a thorough consideration of luany
portions of the subject until other parts of the Atlantic coast have been
examined.
I have the honor to remain, very respectfully, your obedient servant,
N. S. Shaler,
Geologist in Charge.
Hon. Charles D. Walcott,
Director United States Geological Survey.
PREFACE.
As the conditions under which this report has been prepared are of
importance as explaining the nature and scope of the investigations on which
it is based, it is fit that they should be briefly stated. In 1865 I became
interested in the geology of the Narragansett Basin, principally for the reason
that it afforded a convenient district in which students from Harvard Uni-
versity could be instructed iii certain problems of field geology which were
not well presented in the neighborhood of Boston. A number of the frag-
mentary results thus obtained were published in several papers, but the
greater part remained unpublished. With the extension of this desultory
work a general idea as to the structure of the basin and its relations to
some of its more important groups of strata was obtained. In com'se of
time it seemed possible, with a moderate amount of labor, to prepare a
memoir on the field which would add something to the body of information
concerning the area.
About ten years ago, at the request of Maj. J. W. Powell, then Director
of the United States Geological Survey, I undertook to devote the time
which could be spared from more pressing duties to the task of completing
this monograph. Experience soon showed that the mass of detailed work
which remained to be done was so large that it would be necessary to asso-
ciate other persons in the undertaking. To Dr. August F. Foerste was
assigned the southern or bay section, and to Mr. J. B. Woodworth the north-
ern portion of the field. The division of their work was not determined by
a precise line, but was left to mutual understanding. Dr. Foerste's studies
began in 1887. They were interrupted after a few months' labor, but were
resumed in June, 1895, and the field studies were closed in September of
that year. Mr. Woodworth has from time to time been employed in this
field since June, 1891, but the work was discontinuous until the field season
of 1895.
JVION XXXIIT II ■ ^V"
XVIII PREFACE.
In allotting these tasks to Messrs. Foerste and Woodworth, I turned
over to them the small share of the results that I had obtained in work
on this field which seemed likely to be in any way helpful to them.
Those contributions were, however, so limited in quantity, at least as regards
the difficult matters of detailed structure, that the sections of this mono-
graph which appear under their names are essentially their own.
A considerable range of facts, especially those which relate to the inti-
mate structure and the metamorphism of the rocks, have not been to any
extent treated in the following pages. This omission has been designedly
made for the reason that the inquiries necessarj^ to a consideration of these
subjects would have required the services of a trained petrographer for
a long time. In a like manner, the very interesting and important vegeta-
ble remains which abound in certain parts of the Coal Measures have been
passed by, thoixgh they well deserved an extensive study. Thus it has
come about that the extremely varied rocks which border the Paleozoic
stratified series, or which are in the form of islands in its areas, are not dis-
criminated according to their lithological varieties, but are indicated merely
as pre-Carboniferous, and the paleontology of the basin, which includes
extremely interesting groups of fossil insects and other organic remains, is
in no wise presented. These and other omissions deprive this monograph
of all claims to being a full account of the geological phenomena of the
basin; it should, indeed, be considered as a contribution only to the strati-
graphical and dynamic history of the area.
Where the statements of my collaborators are not questioned by me in
footnotes, it should be understood that I approve of them as, so far as I
can see, the best that can be made concerning the facts with which they
deal. In only one instance has conference failed to bring about a concur-
rence of opinion concerning any question of moment. This is in relation
to the value of the division which Dr. Foerste has termed the Kingstown
series, which he regards as distinct from the Aquidneck, which overlies
it. To my mind it appears to be only a local thickening of the last-
named series, with a similarly local addition of sandstones. The dis-
agreement is not only in relation to the propriety of separating these two
sets of rocks, but also as to the thickness of the lower series. It seems
to me most likely that the apparent increase in the depth may be reasonably
explained by the occurrence of rather compressed folds, the axes of which
PEEFACE, XIX
have not been identified, they being hidden either by the waters of the
bay or by the drift covering which conceals the greater part of the surface
of the islands. Nevertheless, as Dr. Foerste, who has given much time
to the problem, remains convinced as to the distinct nature of this series,
it is proper that he should express his convictions in his portion of the
report. The matter is clearly debatable, with the probability that the
truth is on the side of the observer who has the closest personal familiarity
with the field.
It may here be observed that the conclusions of this report, so far as
they relate to the general structure of the basin of which it treats, are
most novel in the matter pertaining to the orogenic history of the field.
The judgment as to the nature of the mountain-building work rests in part
upon observations — in the main unpublished — which I have made in other
somewhat similar basins that lie along the Atlantic coast from Newfound-
land to North Carolina. The general proposition that the basins are char-
acteristically old river valleys which have been depressed below the sea
level, filled with sediments — the sedimentation increasing the depth of the
depression — and afterwards corrugated by the mountain-building forces,
will derive its verification in part, if at all, from study of other troughs of
the Atlantic coast. It may, however, fairly be claimed that the facts set
forth in this memoir show that this succession of actions has taken place
in the Narragansett field.
The contributions to our knowledge respectmg the value of the coal
deposits of this basin are not so great as might well be expected from a
careful study of the field. The truth is that the exploitation of the coal
beds has been done in an extremely blundering manner, so that, while a
large amount of money has been expended during the last hundred years,
the amount of information which has come from it is very small and has
little more than negative value. It may reasonably be hoped that the facts
set forth in this monograph, and advice based thereon, will serve to prevent
other profitless mischances in mining in this area, and make the next work
which is undertaken decisive in its results as to the value of these very
peculiar coals.
The first part of this report is limited to the discussion of certain general
topics which could not well be treated in the special reports of Messrs.
Woodworth and Foerste. This has necessarilj' led to a somewhat incom-
XX PREFACE.
plete presentation of the pi-oblems which the basin affords. It should
furthermore be noted that the party under the charge of the senior con-
tributor is now engaged in studying other basins of the Piedmont or east
Appalachian section of the coastal district. From these inquiries it may be
expected that there will come a report concerning these peculiar features in
the geology of this country. It therefore did not seem worth while to
undertake a more systematic inquiry into the Narragansett field, which
would demand a larger comparison with neighboiing fields than it is possible
yet to make. The reader may also remark the fact that there are but few
diagrams in the text. Owing to the small and disconnected character of the
sections which could be obtained in this basin, it has been found impossible
to represent diagrammatically, in a precise way and for all parts of the area,
the relations of the strata. Under these conditions diagrams are likely to
have a fictitious value — to assert more than the facts warrant. So far as
possible, the pictorial representation of the phenomena has been limited to
local sections and reproduced photographs. It will also be noted that,
particularly in Dr. Foerste's report, attention is called to a great number of
localities Avhich are cited in evidence of the conclusions to which the writer
has come.
N. S. S.
GEOLOGY OF THE NARRAGANSETT BASIN
Part L— GENERAL GEOLOGY
By T^A-THANIEL S0XJTH:G-A.TE; SUTLER
MON XXXTTT 1 1
CONTENTS,
Page.
Chapter I. — Positiou and surface relations of the Narragansett Basin, and the rooks it contains. 7
General features 7
Stratigraphical and orogenic relations 10
Results of the action of orogenic forces 20
Overthrust phenomena - 25
Dike rocks of the basin 27
Chapter II. — Physical history of the hasin 30
Relation to marine and atmospheric erosion and deposition 30
Age of the Carboniferous rocks of the basin 36
Original relation of the Narragansett Basin to the sea 37
Original distribution of the east Appalachian coal field 38
Ancient margin of the basin 40
Relative erosion of east and west Appalachians 40
Recent changes of level - 46
General statement concerning base-leveling 47
Cycles of deposition 49
Arkose deposits of the basin 50
Relation of arkoses to erosion 55
Record value of conglomerates 59
Red color of the Cambrian and the Carboniferous 62
Chapter III. — Glacial history of the Narragansett Basin 64
Carboniferous conglomerates - 64
Last Glacial period 67
Amount of erosion 71
Chapter IV. — Economic resources of the basin 77
Soils - 77
Coals 79
Condition of the beds 80
Characteristics of the coals 82
Conditions of future economic work 85
Iron ores : Iron Hill deposit 88
3
LLUSTRATIONS,
Page.
Plate I. Landscape lookiDg westward across the upper portion of Narragansett Bay, in the low-
land of the Carboniferous area, to the base-leveled area of mainly crystalline and pre-
Carboniferous rocks 7
Fig. 1. Diagram of assumed conditions of compressive strain in rocks in a basin of accumula-
tion 19
2. Theoretical plan of the great folds of the Narragansett Basin 27
5
GEOLOGY OF THE NARRAGANSETT BASIN.
PART I.-GENERAL GEOLOGY.
By N. S. Shaleb.
CHAPTER I.
POSITION AND SURFACE RELATIONS OF THE BASIN, AND
THE ROCKS IT CONTAINS.
GENERAL FEATURES.
The field which in this monograph is termed the Narragansett Basin
consists of a considerable area of stratified rocks ranging in age from the
base of the Cambrian to about the later stages of the Carboniferous period.
The eastern margin of this basin extends on its northeastern side to near
the Atlantic coast in the neighborhood of Duxbury, Scituate, and Cphasset,
or, in this section, to within about 6 miles of the sea. Its northern border,
including the small Norfolk Basin in the area of Carboniferous rocks, lies
in contact with the southwestern wall of what is commonly termed the
Boston Basin. On the west the area is limited by relatively high lands
which separate the trough from the Worcester syncline, a basin which
owes its consti'uction mainly, if not altogether, to mountain-building action
occurring after the end of the Cai'boniferous period. On the south the
Narragansett Basin is partially separated from the sea, at least in those
portions of it which are above the water level, by a constriction formed of
ancient, highly metamorphosed, stratified rocks and a variety of intrusions,
together with some granitic areas which are probably of great age.
7
8 GEOLOGY OF THE NAflRAGAiSrSETT BASIN.
The north-south extension of the Narragansett Basin, including the
related area of the Norfolk Basin, the axis of its greatest length, is from
the southern portion of Narragansett Bay to near Walpole, a distance of
about 50 miles. The east-west diameter, from the western part of Cum-
berland, Rhode Island, to the town of Scituate, Massachusetts, is about
30 miles. Although its outline has many ii-regularities, which will be
hereafter described, the basin has in general a rudely curved form, concave
on the southeastern side. The sections given in a later chapter of this
report show that this trough has great depth, the lowest stratified beds
disclosed on the margins possibly attaining- in its central portions a level
of from 10,000 to 15,000 feet below the plane of the sea. The sections
also indicate that the correlative anticlines, at least those in the western
and central parts of the field, probably had in their original form an eleva-
tion comparable in amount to the depression of the great trough which
they inclose. In a word, the facts indicate that the mountain-building
work effected in this district, and altering the original reliefs, was consider-
ably greater, and gave rise to sharper foldings, than in the more interior
parts of the eastern coast of North America, where the elevations still
retain the mountainous character.
An examination of the structure and attitude of the rocks in this
basin, as will be shown in a detailed way in the later sections of this rejjort,
indicates that this region originally contained an extensively developed
series of pre-Cambrian rocks, the ag'e of which is not yet determinable.
They may for convenience be referred to that limbo of ill-discriminated
formations, the upper Archean (of Dana), or Algonkiau. Above and
probably upon the eroded surfaces of these ancient strata, known in this
report as the Blackstone series, there lie, apparently in detached, much
worn patches, considerable remnants of the Olenellus horizon, or the lower-
most stage of the Cambrian. On top of this formation and the granites
which have broken through it, which were in turn much degraded, come
the Carboniferous beds, strata which, owing in part to their great thickness
and in part to their having escaped the nearly comjolete destruction which
overtook the lower-lying beds, now occupy the greater part of the basin.
The evidence indicates that, on the western border of the basin at
least, the margin of the field was determined before the beginning of Cam-
brian time. At the beginning of the Carboniferous, there is proof that
GENERAL FEATURES. 9
along the eastern border, from near the southern end of Aquidneck Island
to Freetown, Massachusetts, a distance of 35 miles, a granitic area of
considerable extent had already risen above the surface of the sea and
was the seat of no little erosion. This is shown by the fact that along
this line the rocks at the base of the Carboniferous section are made up
mainly of granitic debris, the mass forming a characteristic arkose, at
points so resembling the material from which it was derived that it appears
at first sight to be the product of simple decay in place. Its age is suffi-
ciently indicated by the numerous Carboniferous fossils disclosed by the
pits which have been made in the mass in the search for fire clays. It is
likely — though the evidence is less indicative than that just noted — that
the eastern wall of the basin was in Carboniferous time continued north-
ward as far as the neighborhood of Cohasset. The evidence is to a great
extent from the drift, and is therefore subject to much doubt.
The condition of this basin in the beginning of Carboniferous time was
apparently that of a broad trough penetrating far into the land and
perhaps, though probably not, extending westward so as to include with-
out break what is now the separated basin extending through the central
part of Worcester County southward into Connecticut and northward to
New Hampshire. The very coarse nature of the pebbly — or, indeed, we
may term it cobbly — waste which occurs in the upper part of the Carbon-
iferous, appears to indicate that the trough must have been shallow. This
conclusion is afiirmed by the tolerably uniform distribution of the pebbles,
some of them a foot or more in diameter, across the basin on the line from
Fall liiver to Attleboro.
On the assiimption that the Nai-ragansett Basin was shallow at the
beginning of the Carboniferous period, and on the supposition that in the
center of the field these beds attain a depth of several thousand feet, it
seems necessary to assume that the erogenic work was in part accomplished
during that time. The history of the basin can be best explained by the
hypothesis of an extensive subsidence of the land within the limits of the
trough as the beds which it contains were laid down, and a corresponding
overlap invasion of the sediments, which constantly removed the shore
lines farther away from the center of the basin.
After the close of the Carboniferous period the Narragansett district
was evidently the seat of yet further mountain-building actions, which led
10 GEOLOGY OF THE NARRAGANSBTT BASIN.
to extensive dislocation of the deposits and to the formation of several
anticlines and synclines, as well as to the development of considerable fault
movements. In this part of their history the rocks which remain in this
field were probably deeply buried beneath accumulations which have been
entirely swept away. This fact, as will be shown in detail hereafter, is
indicated by the large amount of pebble deformation which has taken place
in various portions of this field.
Tlae foregoing statements make it plain that the detailed consideration
of the Narragansett Basin should be preceded by some study of the strati-
graphical and orogenic features of the district in which the basin lies.
STRATIGBAPHICAL AND OROGEISTIC RELATIONS OF THE BASIN.
The relation of the Narragansett Basin to the system of disturbances
which have afiFected the eastern coast of North America involves certain
questions concerning the organization of the Appalachian system which,
so far as I am aware, have never been considered by the students of that
field. Those mountains are generally assumed to consist in part of an
ancient axis, which was developed perhaps by a succession of movements,
partly in Archean and partly in early Paleozoic time, the whole forming a
range extending from northern Alabama to the northern parts of New
England, with a somewhat obscure continuation through Nova Scotia and
Newfoundland to a contact with the old Labrador element of the Lauren-
tian Mountains. To the west of the ancient axis of disturbance of the
Appalachians, the Allegheny range or series of ranges has been recognized
as a development which took place after the close of the Carboniferous,
bringing about the formation of some score of considerable folds, all of
which, except those in the extreme south, retain their relief This AUe-
ghenian division extends, with diminishing size of folds, as far north as
near Albany, New York -^
West of the Alleghenies, throughout their whole extent, from Alabama
to the Mohawk River, there is a table-land which manifestly owes its uplift
also to the orogenic work that resulted in the formation of the anticlines
and synclines which were produced to the west of the old axis after the
' It is characteristic of tlie Alleghenian division of the Appalachians that it consists of prevail-
ingly long folds, which are much compressed and generally lie in such a position that an ea-st-west
section of the field traverses four or five of the similar anticlines.
strat[graphii;al and orogenio relations. 11
close of the Carboniferous period. This table-land is well exhibited in the
plateau of central Tennessee, but is most strikingly shown in the degraded
remnant of its northern part, known as the Catskill Mountains.
It has not yet been sufficiently recognized that to the east of tne old
Appalachian axis there was a great series of mountain ranges, now obliter-
ated, which extended from the southern part of North Carolina along the
Atlantic coast as far as Eastport, Maine. The reason why this portion of
the system has been neglected is found in the fact that the structures which
belong to it are peculiar in form and have been so far worn away that they
present no considerable topographical reliefs. The region has the general
character of a country which has been brought near to base-level, and the
determination of the position of the ridges and furrows can be made only
from the attitudes of the rocks. In fact, in the present state of our knowl-
edge of this section of the country, only a few of the old troughs are
recognizable and the position of the folds is not well made out.
Beginning on the south, we find the southernmost of these folds, so far
as they have been recognized, in the Dan River Basin of North Carolina.
Farther north, the Kings Mountain district appears to indicate the seat
of another folding, a part of the rocks involved in the movement being so
hard that they have not yet been completely eroded. In the Richmond
coal field an extensive series of beds, probably of Triassic or Rhaetic age,
indicates the presence of another considerable basin, which has something
like the area, depth, and general form of the Narragansett downfold.
From studies of the Richmond Basin, made at various times, I have
become convinced that the depth of the depression in its central parts
probably exceeds 3,000 feet, and may be twice that amount, and that, in
part at least, it is separated from the sea by an area of uplift which is now
worn down to its granitic base.
To the north of the James River Valley in eastern Virginia the Triassic
rocks are again found involved in relatively deep, broad troughs, the forms
of which are not jet well made out. There are probably several of these
troughs, some of which contain ancient stratified rocks of undetermined
age that may belong in pre-Paleozoic time. From the Potomac River
northward, owing to the mantle of Cretaceous and Tertiary waste, we have
no distinct indications of this series of foldings until, in New Jersey, we
again find the Trias involved in troughs. East of the Hudson the broad
12 GEOLOGY OF THE NARRAGANSETT BASIN.
trough of the Connecticut Valley may be regarded as in its nature essen-
tially equivalent to the more southern basins, the only substantial difference
being that on both sides it is bordered by a wide field of high-lying ancient
rocks, which extends eastward nearly to Worcester and has a height that
is not found in the case of the walls on the Atlantic side of the more southern
basins.
At Worcester we come upon the most southern of the troughs on the
eastern side of the central Appalachian axis in which well-determined Car-
boniferous rocks appear. The form of this basin is not well known, but,
from what has been learned concerning it, it appears to be relatively narrow
and long, having in general a closer resemblance to the synclines of the
Alleghenies than any other of the troughs in the group which we will here-
after term the East Appalachians. The Narragansett trough is next in order,
but, as it is to receive special treatment, it may here be dismissed with
the brief statement that in its type of form and in the nature of its dis-
locations it differs from the West Appalachian or Allegheniau series of
dislocations.
North of the Narragansett district we have in the Boston Basin a con-
siderable downfold, the axis of which extends in a prevailing east-west
direction, the depression having a characteristically great proportionate
width and an irregular form which belongs to the other East Appalachian
depressions.
From the Boston Basin northward the complicated and imperfectly
known geology of the country indicates a succession of these basins dis-
tributed along the coast of Massachusetts, New Hampshire, and Maine to the
New Brunswick district. One of these occurs at Newburyport; another is
traversed by the Penobscot River; others lie between Mount Desert and the
outer Cranberry Islands and to the north of the Mount Desert Mountains ;
yet another, or perhaps two partly separated basins, are to a great extent
occupied by Cobscook and Passamaquoddy bays ; still others exist along
the coast of Maine, though their outlines have not been traced. The Car-
boniferous areas of New Brunswick and Nova Scotia appear to have been
preserved in basins having the general character of the East Appalachian
troughs
Reference has already been made to the decided differences in the
forms of the folds which occur on the two sides of the old Appalachian axis.
STRATIGEAPHICAL AND OROGENIO RELATIONS. 13
Those on the west are narrow, relatively long, and consist, with slight
exceptions, of simple foldings of the true anticlinal type. Those in the
eastern or seaboard district are in general rudely oval in form, their length
usually not exceeding twice their width. They are, in fact, broad troughs,
the included strata being cast into a number of anticlines and synclines.
This peculiar difPerence of form leads naturally to the sujDposition that the
history of these two groups of depressions has been diverse. An inspection
of the deposits verifies this supposition. It has already been stated that
the Narragansett Basin was an ancient trough, formed before the Carbon-
iferous period, in which, during a process of subsidence, the beds of the
Coal Measures were accumulated. The evidence derived from the study
of the Richmond, the Connecticut River, the Boston, the Moimt Desert,
and the Passamaquoddy basins has satisfied me that the troughs are of
ancient date, that they were filled to a considerable extent with materials
imported from the higher country about them, and that this filling process
was associated with progressive local subsidences.
The foregoing considerations seem to me to warrant the supposition
that the East Appalachian basins, or at least the greater part of them, were,
in the beginning of their formation, erosion troughs, which became the
seats of excessive deposition, and this brought about the lowering of their
surfaces in relation to the original bed. In a word, they were downpressed
by the weight of the burdens which came into them. At a subsequent
stage the mountain-building forces, acting irregularly, compressed these
troughs, producing the sets of local disturbances which are exhibited by
each field. A possible instance of such local orogenic action in very
modern times, as late as the Pliocene, is found in the tilted strata of the
Marthas Vineyard district. In this case excessive deposition of a local
character has been followed in turn, first, by subsidence, and then by com-
pressive action, producing a large measure of folding, in a general way like
that which has taken place in the neighboring Narragansett Basin, which
lies immediately on the other side of the anticline that forms the eastern
boundary of the Narragansett trough.
It should be said that the hypothesis of the antecedent erosion of the
basins which we are discussing has a considerable measure of support from
the very diverse orientation of the axes of the East Appalachian troughs
These range from east and west to north and south, a diversity which
]4 GEOLOGY OF THE NARRAGANSETT BASIN.
seems to me to be inconsistent with the supposition that they have been
formed through the action of such accurately determinate strains as
produced the Alleghenian ridges. The last-named foldings are of the
normal mountain type. The axes are parallel for great distances, and
where the ridges change their orientation they preserve their parallelism
and alter their general course with rather gentle curves. They exhibit no
case of such contrast in the axes of the basins as is shown in the adjacent
Narragansett and Boston troughs.
The known facts concerning the effects arising from the accumulation
of thick sediments warrant the supposition that wherever this action occurs
it is likely to be attended by a subsidence which, though of a local char-
acter, may attain an extent proportionate to the influx of the debris.
Wherever along the coast line long-continued land erosion forms deep
valleys, these depressions are likely to be, during a period of subsidence,
the seats of extensive deposition. Where the amount of this sediment is
sufficient to develop the downcast movement, it may lead to the formation
of a trough of great geological depth, though it may at all times be shallow
water or even retain the state of a delta area. It therefore does not seem
a matter for surprise that the Atlantic coast district should exhibit basins of
this nature, for, although this coast of the continent has been subject to
many alterations of level, there is abundant evidence to show that from the
Cambrian period to the present day the eastern front of the land has been
often, indeed we may say prevailingly, somewhere near its present position.
There has been ample time for the formation of many great coast erosion
troughs and for their filling with sediments .to the amount which the
hypothesis requires. The final development of anticlines within the troughs
in the extensive way in which they appear to have been formed may
readily be explained by the existence of the same compressive tensions
which have operated in the West Appalachian field, the difference being
that in the East Appalachians the form of the troughs somewhat controlled
the direction of these anticlines, while in the western portion of the system,
a newly emerged part of the continent, they appear to have been guided
in their alignment in a much greater measure by the direction of the com-
pressive strains, there being no strong topographical features except the
old land on the east to determine the trend of the upcurving.
At the present time, although the Atlantic coast of North America has
CONDITIONS OF DEPOSITION OF BEDS. 15
been subjected to recent and important alterations of level, there are many
considerable basins along its shores which appear t6 be, in their structure
and history, much like those which, according to the hypothesis we are
discussing, were developed along this coast line during the Carboniferous
period. Albemarle and PamHco sounds, and the bays of the Chesapeake
and Delaware, need only a continuance through a considerable extent of
geological time of the conditions which now exist to bring about the
formation of accumulations essentially like those under consideration. So,
too, certain basins along the Gulf of Mexico, particularly Mobile Bay and
the trough of the Mississippi, are the seats of extensive estuarine accumula-
tions which in the ages to come may take on much the same aspect as the
Narragansett Basin.
A little consideration will show the reader that a river valley in its
lower parts naturally becomes the seat of sedimentation. An inspection of
the maps of shore lines will make it plain that more than half the great
rivers of the world have the lower parts of their valleys flooded in a way
which clearly indicates that these estuarine regions have recently been
brought beneath the level of the sea and thus converted from fields of
erosion to those of deposition. The generality of the fact that the great
rivers, notwithstanding the CAddent tendency to accumulate delta deposits
about their mouths, enter the sea through their own submerged valleys, is
probably in many cases to be accounted for by the fact that, while the con-
tinental masses as a whole tend rather constantly upward, their shores,
being near the seat of maximum sedimentation, naturally tend downward,
in the manner now recognized as resulting from the imposition of a great
load of sediments on any part of the earth's surface. We may therefore
regard the occlusion of river valleys by excessive sedimentation, which
takes place coincidently with the subsidence of the trough below the
level of the sea, as a normal feature in the history of any shore which is
intersected by river valleys.
If the hypothesis which is here adduced to explain the main peculiar-
ities of the East Appalachians be established, it is clear that, considered
from the point of view of their origin, we must accept a new specific group
of mountains, one characterized by features in the main determined by the
fact that the beds of which they are composed have been laid down in a
formerly existing erosion basin, originally due to stream work, though it may
16 GEOLOGY OP^ THE NARRAGANSETP BASIN.
have been orographically deepened by the suosidence caused by sedimenta-
tion. It will be seen that this view has a certain superficial resemblance to
the hypothesis commonly known as James Hall's, in which mountains are
explained by supj)Osing, first, the accumulation of a thick series of beds;
second, a subsidence of the crust, due to the deposits, bringing about a
folding of the beds; third, a massive uplifting of the foundation on which
these foldings rest, so that the ridges come to stand on a lofty pedestal. I
would not have it supposed that there is any real similarity between these
hypotheses. The essential difiiculty of the hypothesis which endeavors to
explain the formation of mountains first by subsidence and then by eleva-
tion, is that there is no sufficient means indicated whereby the reelevating
process can be brought about. There is also much reason to question
whether the downsinking movement could develop the arches of the strata.
In the view which I am advocating, the conceptions are much more simple
and rest upon more patent facts. The steps of action which are postulated
are as follows: First, the excavation in ancient and compact rocks, in their
nature good transmitters of thrusts, of a trough or basin such as is likely
to be formed in the estuarine section of a considerable river; second,
the filling in of this basin by sediments accumulated during a downward
oscillation of the area in which the basin lies; third, the development of
compression strains, such as are involved in rock folding, the relief being
afforded by the folding of these stratified deposits.
If this hypothesis as to the origin of the Narragansett foldmgs were
correct, we should ex^Dect to find the maximum of disturbance in the extreme
mai'gins of the basin, the central features of the area remaining less dis-
turbed. As will be seen from the chapters on the deposits of the basin,
this is essentially what we find. Wherever the area is of sufficient width
to afford a field for the deA^elopment of the structure in a clear way, we
observe that the indications of lateral stressing are very clear in the belts of
country next the contact with the crystalline rocks, while in the central
portion of the field the beds exhibit lessened stress. Thus, as will be seen
from fig. 1 (p. 19) and the sections across the basin where the distance is not
far from 20 miles, we find the marginal portion of the stratified rocks exceed-
ingly flexed, the resulting dislocation attaining' about the highest order of
complexity, while the intei'mediate field, including much more than one-half
the whole length of the indicated line, is less marked by the stressing forces.
STEATIGRAPHICAL AND OROGENIC RELATIONS. 17
Where the Narragansett Basin narrows, as it does in the southern third
of its length, the type of the folding differs somewhat from that above
indicated. In place of the folds on either side, with a less disturbed
middle field, the whole of the section is folded into a few great trough-
shaped undulations, with some minor irregularities. Yet the fact that the
strains entered the bedded rocks from the sides is shown by the character
of the bottom of the great North Aquidneck syncline. The form of this
part of the basin is tolerably Avell known by the mine workings in the
northern part of Aquidneck Island. These explorations show that the cen-
tral portion of this area has in a measure escaped the disturbing influences
which have perturbed the beds next the margins.
Besides the evidences of stress which are shown by the extensive
dislocation of the stratified rocks of the Narragansett Basin, we must note
the equally characteristic marks of compression afforded by the interstitial
movements which the rocks have undergone. These changes of position
of the rock materials are exceedingly common in the metamorphic part of
the field (see fig. 6, p. 120) and for a short distance to the eastward, and are
readily observed wherever there are any data by which they may be judged.
Wherever the rocks lying near the eastern and western margins of the
basin contain organic fossils or pebbles, save of quartz, a slight examination
will in practically all cases show that those bodies have been more or less
elongated, the direction of their extension usually being on horizontal lines
which are approximately parallel to the neighboring margin of the basin.
At many points it is evident that the elongation of the pebbles or fossils
has been as much as 50 per cent of their original diameter on the given axis,
and sometimes it exceeds this amount. It commonly happens that the
distortion Avas sufficient to convert, a circular disk lying in the axis of the
movement, and having a diameter of a foot, into an ellipse having a major
axis of 2 feet and a minor axis of 6 inches. In rare instances the alteration
of form appears to go much beyond this proportion. I suspect, indeed,
that at a few points it is obscurely traceable to three or four or even five
times the original length, but in these higher terms of the series fossils
become mere blurs and pebbles lose all semblance of their original
character.
Although solid bodies like quartzite pebbles may often be found
stretched to the amount of 50 to 100 per cent, it is generally easy to see
MON XXXIII 2
18 GEOLOGY OF THE NARRAGANSETT BASIN.
that the matrix in which they are embedded has been much more extended
than the more I'igid inchisions. This is shown by the fact that near each end
of the axis of the pebble in which the elongation has taken place there is
often a slickensided surface, showing that the matrix pulled away from the
sides of the stone and slipped by them, while at the very end we note the
existence of a vein deposit which is also slickensided after the manner of
most veins, the structure showing that the movement which pulled the matrix
away from the inclosed fragment operated slowly and by successive steps.
It often happens that pebbles, especially those of large size and of the more
rigid varieties of stone, show no distinct signs of elongation, and yet they
have these appended veins and the slickensides, indicating that the more
plastic matrix has yielded to the pressure which has been imposed upon it.
Thei'e are certain features in the distribution of elongated rock masses
which appear to throw some light on the questions we are now considering.
In the first place, we note that in the Narragansett Basin, and, so far as my
observations go, iia the other basins of the East Appalachians as well, the
plastic migrations of the strata, as shown by the distortion of fossils and
pebbles, are decidedly more common in the marginal parts of the several
fields. These elongational phenomena are strikingly manifested at many
points in the southern portion of the Narragansett area. In the central
part of the area there are extensive tracts of conglomerate where a close
examination has failed to indicate either that the pebbles were stretched or
that the matrix was forced by these inclusions. This goes to show that the
force which affected the stratified rocks came upon them as a thrust hori-
zontally transmitted from the field of crystallized rock on either side.
The other point concerns the regional distributions of plastic migration
of rock. This phenomenon seeiias to be of common occurrence in the East
Appalachians from New Brunswick southward. It is excellently shown at
the Cobscook Basin, about Mount Desert, and in the Boston Basin; in the
basins to the southward it is more scantily exhibited. Curiously enough,
however, this feature appears to be prevailingly lacking in the rocks of the
West Appalachians, notwithstanding the deposits of that section appear to
have been on the average about as much dislocated by folds and faults as
have those of the eastern section. It is not clear to what the greater plastic
movement of the eastern rocks has been due. It may, however, be sug-
gested that sucli movements depend upon the compression of rocks while
STRATIGRAPHICAL AXD OROGENIC RELATIONS. 19
Tinder a deep cover of overlying strata and therefore at temperatures which
woukl in a large measure diminish their rigidity. This does not seem a
satisfactory explanation, for the reason that while the amount of strata which
has been removed from these eastern mountains has probably been larger
than is the case with the western ranges, the erosive process, at many points
in the west, has gone far enough to reveal the bases of the anticlines and
synclines, even as it has done along the Atlantic coast. It has been noted
that the eastern basins are generally, exce^it perhaps that of the Dan River,
much more intersected by dikes and stocks than are those of the west, where
there are but few such intrusions known, perhaps in all not over a dozen
between the Catskills and Ala-
bama, as against the thousands
which may be traced in the moun-
tain-built area of the Atlantic coast.
Xt seems reaSOnaDJe to assume Fiq. l. — Diagram of assumed conditions of compressive strain i
that thp PTtpnsivP nln«^hV mnvP- rocks in a basin of accumulation. AA, massive crystalline
inai me exieusive piaSUO move ^ocks. BB, the rocks of the basins. The arrows indicate the
mentS of the rocks in tlie East Ap- di™«t.ion of the compressive strains; the spaces between their
i heads indicate the measure of the yielding at the several points.
palachian district are related to the
igneous action which has occurred in this field, and that the two groups of
facts show that the modes of action of the mountain-building forces in the
two districts were in some ways very different. I venture to suggest that
the difference was partly due to the conditions of the superficial rocks in the
two fields. In the west the surface of the country from northern New York
to Alabama was, at the time of the elevation of the West Appalachians, again
occupied by relatively unbroken strata which lay on the surface of the upper
Paleozoic rocks. The stresses of comjoression which assailed this wide field
when the conditions of resistance were uniform affected all parts of it in
an approximately equal degree. In a limited way, in northern Alabama,
Georgia, and Tennessee, where the conditions were diversified, the stresses, as
shown by Hayes, were in some cases locally accumulated and so discliarged
as to bring about extensive overthrusting ; but in general the folding was
approximately equal for each unit of the section which was stressed. There
was, in a word, no transfer of thrust through great beams of massive and
therefore unyielding rock to fields where the stress could take effect on the
easily folded strata On the Atlantic slope, however, the conditions led to
the local intensification of the stress phenomena. Between the deep basins,
20 GEOLOGY OF THE NAKEAGANSETT BASIN.
filled with their bedded rocks, lay fields of crystalline materials which had
been compacted by previously administered presstu-es and the accompany-
ino- metamorphism until they had been In-ought to the most rigid or the
best thrust-transmitting state to which rocks may attain. The result was
that the compressive strains were transmitted through these ancient close-
knit blocks of strata to take- effect on the frailer materials which were
inclosed in the troughs between their edges. The assumed conditions are
in a diagrammatic way represented in the accompanying figure (fig. 1).
RESULTS OF THE ACTIOI^^ OF OROGENIC FORCES.
So far as can be determined by the evidence which has been found,
the orogenic movements which flexed and fractured the Carboniferous rocks
of the Narragansett Basin did not affect in a similar manner the more
ancient formations which border the area. There are, it is true, certain
faults intersecting the margin, particularly on the northern side of the area,
which c\it through the Carboniferous beds and the fundam.ental complex
alike, but there is no evidence that these faults extend very far beyond the
margin or that folds attended the formation of the rifts. Any system of
anticlines and synclines affecting the more ancient beds would, we may
fairly presume, have left their marks in the distribution of the deposits as
they appear on the present surface. The several groups of metamorphosed
beds would appear in parallel bands, an arrangement which they do not
exhibit.
The only distinct feature in the ancient compact rocks which can be
attributed to compressive action is the system of shearing planes which
have been extensively developed in the massive rocks on the margin of the
basin. Where these have been developed in the granitic rocks they have
given the latter a gueissoid aspect. These secondary structures are most
distinctly marked near the contact borders on the east and west, and appear
to diminish as we pass a few miles from the present margin of the Carbon-
iferous field. The existence of this class of distortions in the rocks, along
with the general lack of evidence of folding, points to the conclusion tliat
the pressure affected these compact formations in a way different from
that in which it affected the stratified beds of the basin. It may be tliat
the yielding in the interstitial movements accomplished a certain reduc-
tion in the length of the sections even when the materials were too rigid
EESULTS OF THE ACTION OF OEOGENIO FOECES. 21
to permit them to take on the normal folds which afford the natural
means of shortening in stratified beds.
Since the shearing planes of the massive rocks grow less evident as we
go away from the margin of the basin, and have not been clearly observed
beyond the limits which are likely to have been occupied by its deposits,
the question arises whether these planes are not a consequence of the
movements which must have occurred in the rocks that lay beneath the
Carboniferous strata at the time they were folded. That some form of
distortion affected these basilar dejDOsits must be assumed, but the jjrecise
nature of the movements is not known.
The type of folding exhibited in the stratified rocks of the basin is
clearly that of ordinary synclines and anticlines Avhich have been carried
to a rather advanced stage of development. As will be noted from the
maps, the axes of these folds trend nearly north and south in the southern
portion of the basin, but in the northern part they incline to the eastward,
and in the east attain a position nearly at right angles to the southern folds.
This turn of the structural axes seems to be due to the existence of the
broad eastern bay, which is a notable featiire of the basin.
There is another noteworthy feature in the form and distribution of
the anticlines which appears to be closely related to the peculiar history
of this basin; this is clearly exhibited in the accompanying diagrammatic
section (fig. 2, p. 27), which shows the attitudes of the folds in the central
part of the field along a line from north to south. In this section the
compressive action has operated to create strong folds next the borders of
the basin. These folds have their steepest slojjes toward the margin, the
sides toward the center of the basin being much less inclined, so that
by erosion of the declivities of the anticlines on either side a relatively
broad trough is formed in the central part of this field. So far this relation
of the slopes of the upper folds to the margins of ancient massive rocks has
been distinctly traced only in the northern half of the mountain-built
district, but there are indications that it exists also in the southern portions
of the field, being there concealed by the waters of the bay or masked by
the prevailing covering of drift.
The disposition of the strata as above noted appears to require the
supposition that the thrust acted from either side in such a manner that the
central portion of the basiii was a relatively neutral zone in the vaulting
22 GEOLOGY OP THE NARRAGANSETT BASIN.
movements. If the strain which produced the folding was of equal value in
all parts of the basin, there would be no reason why the resulting arches of
the strata sliould not have been of ui:iiform declivity on either side. I can
best account for the facts in this case by supposing that, while the contraction
which brought about the mountain building may have acted in all parts of
the field, a large part of the stress was carried through the lateral girders of
indurated massive rocks on either side of the basin rmtil it could be applied
to the newly formed, distinctly layered, and therefore less resistant materials
contained in the old Narragansett Basin.
The horizontal value of the movement which was taken up in the fold-
ings of this field can not as yet be accurately computed. The attitudes of
the beds, however, indicate that it amounted to 2 miles or more. The con-
ditions of this action may be considered as such that the surface of the cen-
tral part of the disturbed area may not have been moved except down-
Avardlv, while the longitude and latitude of the points on the surface on
either side jvhich were affected by the foldings were evidently changed in
an increasing measure as we depart from the central axis.
The depth of the distinctively stratified rocks in the basin at the time
the mountain-building work was done can not well be reckoned at less
than that of the existing section, but as this region has been subjected to
an amount of erosion competent to bring the anticlines and synclines to
about the same level, it may well have been near double that aniount.
Therefore we may assimie the depth of the section of massive rocks which
conveyed the thrust from an extreme area on either side to the deposits of
the trough as not less than 2 miles.
It is not yet clear whether the mountain-building action which has
affected this basin was altogether accomplished after tlie latest-fonned beds
which it now contains were accumulated. The factthat all the sections of the
Carboniferous series were accumulated in shallow water, or but little above
its level, requires us to suppose that the trough was the seat of a nearly
continuous depression. It is to be expected that the downsinking would
have been accompanied by some measure of compressive movement. So
far, however, the field has afforded no evidence of such mountain-building
work done during the subsidence of the trough. On the contrary, the
observations are most reconcilable on the supposition that the whole of
the strictly erogenic action took place after the work of depression was
RESULTS OF THE AOTION OF OROGENIO FORCES. 23
complete. In fact, it can not be believed that there was any distinct rela-
tion between these two movements — that of general downsinking- and that
of warj^ing nnder the influence of the lateral thrusting.
It may be noted that the conditions of mountain building in this basin
resemble in a general way those of the Appalachian district, with the excep-
tion that in the latter region the neutral axis appears to have been in the
line of the ancient belt of the Blue Ridge or its equivalent ranges to the
north and south. Against this central ridge the thrusts apparently came
from the east and west. Moreover, in this Appalachian field the com-
pressive action seems to have been distributed over a much wider section,
with the result that the amount of deformation per unit of length in an
east-west direction was much less than was the case in the Narragansett
Basin. The folds are, on the average, less crowded together, and the
synclines are wider; in other words, the evidence goes to show that, in
proportion to the size of the disturbed area, much more movement was
taken up in folds in the Narragansett Basin than was the case in any part
of the West Appalachian field of disturbances.
The relation of the mountain-building work of the Narragansett Basin
to similar action in the neighboring fields is a matter of much interest.
There are three of these areas that deserve special notice — the Connecticut
Valley, Marthas Vineyard, and Boston Basin. Of these three regions of
mountain-building action, the one most remote — the Connecticut — is in all
respects the most unlike the Narragansett Basin in its orographic features.
In the Connecticut Basin we have what appear to be the same general
antecedent features noted in the Narragansett Bay. There was a preex-
isting valley, which was deeply and rapidly filled by detrital materials. It
is likely that this accumulation took place during a j)eriod of subsidence;
it evidently occurred after the deposits of the eastern trough had been
formed, and under conditions which led to the extravasation of large
amounts of lava. When the Connecticut Basin was subjected to compres-
sive action, the yielding was by the rupture and shearing of blocks, with
little trace of folding. It seems most probable that the hypothesis adduced
by Prof W. M. Davis — which is, in effect, that the easily fractured planes
of the basement rocks of the area, which are composed of schists standing
at a high angle, induced the for^nation of faults rather than folds — accounts
for the departure of this region from the type of mountain building else-
24 GEOLOGY OF THE NARRAGAISrSETT BASIN.
where to be observed in the New England troughs. In a measure, the dis-
tinct folding of the neighboring trough deposits on the east, occurring where
the basement beds are of an essentially nonschistose character, seems to
bear out this hypothesis.
In the Mal'thas Vineyard area of distortions there is no indication of
a trough. There are no ancient rocks rising above the plane of the sea. It is,
however, quite possible that the northwestern border of the basin, if we
assume such to have existed, was in the bed rocks of the neighboring main-
land and that the seaward border has been worn away by marine action or
lies depressed below the sea level. It is to be noted that the prevailing
axes of the dislocations on Marthas Vineyard indicate a pressure acting
from the northeast and southwest, with resulting foldings Avhich are mainly
aligned in a northwest-southeast direction, or approximately at right angles
to the usual trends of the Narragansett and other folds of this part of
the continent. Although it seems to me probable that these crumplings
of the Cretaceous and Tertiary beds of Marthas Vineyard Avere formed in
a trough which was filled in these ages, the evidence on this point is not
clear. So, too, with the dislocated deposits of Block Island. It will there-
fore be best to pass these areas by with the remark that the forms and
trends of their orographic reliefs differ widely from those of the older dis-
turbances, and that some of their pecidiarities, especially the faultings and
complications of their folded strata, may be due to the fact that the move-
ments occurred near the surface, without the restraint which is imposed on
beds, such as those in the Narragansett area, compressed while under a
thick mantle of deposits which have since been removed.
In the Boston Basin we find series of rocks which have the same
general character as those in the Narragansett Basin. To a great extent,
the rocks, as regards their structure, are fairly comparable to those in the
Narragansett district. Although the evidence is not perfectly clear, it goes
to show that there was the condition of a preexisting basin, which was
formed sometime after the horizon of the pre-Cambrian, and which received
the deposits of the Roxbmy conglomerate period, which make up the greater
part of the accumulations. As yet the age of these conglomerates and
the associated rocks is not determined, a most assiduous search having
failed to reveal fossils of determining value. Therefore it is not possible to
fix the earlier limit of the disturbances. Still, the immediate contact of the
OVERTHRUST PHENOMENA. 25
basin on the north and south and the approximate parallehsm of the axes
of their foldings appear to indicate that the strains took effect on them at
approximately the same time.
Complicated as is the structure of the Narragansett Basin, that of
Boston Bay is yet more involved. Although some minor folds may be
traced in it, and larger arches are fairly to be assumed, the area as a
whole appears to be much less massively and continuously flexed, and
more faulted, than that on the south. It is, raoreo^^er, far more generally
penetrated by dikes than is the Narragansett field. Its type of structure
seems to be between that of the last-named basin and that of the Connecticut.
It is probably owing to the relatively deep erosion of the Boston Basin
and the large amount of faulting in the erogenic work that it is so
difficult to recognize and determine the elements of folding which have
existed.
OVERTHRUST PHENOMElSrA.
The phenomena of overthrusting which occur in the development of
mountain dislocation ha-s^e of late been the subject of much profitable
inquiry. It is therefore worth while to examine into the question of their
occurrence in this basin. As will be noted in the sections, the only
portions of the field where accidents of this nature seem to be indicated are
in the district extending from near Providence to the northern boundary of
the basin. The reason for this may be that only in this part are the
attitudes of the rocks near the margin sufficiently disclosed to make a close
interpretation possible. Particularly in the region about the Attleboros
the positions of the dislocated strata favor the view that the beds have been
at first folded and then thrust over, usually toward the less-disturbed centers
of the stratified rocks, so that a certain amount of migration of the beds has
been brought about. How far this has led to the disruption of the folds, so
that the masses which have changed place have been rent away from the
beds of which they originally formed a part, can not be determined from
the data, now in hand.
It is probable that the original margin of the Carboniferous rocks in
this basin was farther away from the center than it is at present. The
process of erosion, which has attacked the massive crystalline rocks of
the bouiidaries as well as the stratified interior parts of the trough, has
most likely lowered the whole of southeastern Massachusetts to the extent
26 GEOLOGY OF THE NAREAGANSETT BASIK
of several lumdrecl, perhaps to the depth of 1,000 or more, feet, the result
being that, as the old bordering walls had an erosion slope, the margin is
at present perhaps some miles nearer the center than it was when the folding
was done. It has also been noted that the folding and other evidences of
stressing which the rocks present diminish, except on the northern border,
as we pass from the margin toward the interior of the Carboniferous area.
These considerations lead us to see that the portions of the beds which were
most dislocated have been removed by the erosion process, which, as is
shown by the planed-down character of the surface, has undoubtedly been
very active in this part of the continent. It is therefore not unlikely that
great migrations of strata took place at the time of the disturbance, the
indications of which have been entirely lost to us by the process of decay
and removal of the beds which were involved in the movements. In a
word, the zone where we might most naturally suppose the overthrusting
actions to have taken place has in large part disappeared, at least so far as
the superficial beds are concerned.
From the conditions presented by this basin there is reason to believe
that the rupture and horizontal displacement of folded strata would be more
likely to occur here than in the ordinary instances of mountain folding.
Under the usual circumstances, where the contracting impulse afi^ects a
large extent of country, influencing all the rocks alike, the relief effected
bv the corrugations of the strata is apt to be eqiial in all parts of the area
subjected to the movement. When, however, as in the Narragansett dis-
trict, the strains were most applied on the margins of the field, where the
tensions developed in a wide extent of country were localized in a narrow
zone of relatively weak strata, we must expect the highest type of distortion
and rupture that occurs in mountain- folding Avork.
Such overthrusting as has occurred in the Narragansett Basin appears to
a great extent to have been begun by folding, the arches being raised to a
considerable height. These arches appear to have collapsed, as all com-
pressed arches tend to do.
Overthrusting action appears to be most probable in the region between
the villages of North Attleboro and South Attleboro, where the relation of
the red Wamsutta series to the gray rock on the south requires the supposi-
tion of this movement. So far as has been observed in the few traceable
OVERTHEUST PHENOMENA.
27
faults, there is no tendency of faulted blocks to ride over one another. It
can readily be luiderstood that, inasmuch as this region has been subjected
to very extensive erosion, overthi'usting which was preceded by the collapse
of the folds might have all the marks of its former existence destroyed by
the removal of the strata which were involved in the movement.
An ideal section (fig. 2) drawn by Mr. Woodworth through the three
great synclines in which the Dighton group appears, including the Attleboro
syncline on the noi'th, the Grreat Meadow Hill trough in the middle of the
basin, and the Swansea syncline on the south, exhibits a symmetry in the
cross section which is further evidence of the simplicity of the larger
features of structure of the central part of the basin. There is along this
line of section a great broad syncline in the middle of the basin. It has
nearly symmetrical slopes with relatively low dips. The synclines parallel
sy/7c///}e.
Gt.Afeac/o<A/ /////
2yr>c///
S^vansea
s/nc//'ne
Fig. 2.— Tlieoretical plan of tbe great folds of the Narragaiisett B:
with it on the nortli and south have their axial planes inclined away from
the middle syncline, or, in other words, the sides of the synclines facing
the middle area are nearly vertical. A plane lying in this region of
folding would have been deformed so as to give a cross section like
that in fig. 2. lliere is in this case no prevailing pitch of the axial
planes to or away from the ocean or an older land mass, but rather a
symmetrical deformation of beds with reference to the middle line and sides
of the basin as it now exists.
DIKE ROCKS OF THE BASIN.
Although, as before stated, the systematic study of the igneous rocks
of this area has not been undertaken, there are certain features connected
with their distribution which deserve notice. These concern the areas in
which the intrusions occur and the portions of the great section which they
traverse.
28 GEOLOGY OF THE NARRAGANSETT BASIN.
So far as has been observed, all of the numerous intrusions occur on
the marginal portions of the basin, mainly on its western side and in the
prolongation of the area in what is known as Norfolk Basin, a field which,
as elsewhere noted, is not much considered in this report. The eastern
margin of the area is not so well revealed as the western, but, as will be
seen in the detailed descriptions of Messrs. Foerste and Woodworth, with
the exception of the felsite dike in Plympton, no intrusive masses have been
discovered on this margin. Dikes also occur, as indicated in Dr. Foerste's
reports, on the southern portion of the field, but not so abundantly as on
the western versant. So far as the observations go, they make it improb-
able that, in general, any dike attains the surface at a point more than 2
miles toward the interior from the border of the Carboniferous field. An
exception to this statement must be made in the case of the Wamsutta field,
where, perhaps owing to the large amount of disturbance the beds have
undergone, dikes are found at a distance of nearly 4 miles from the western
border.
It may also be remarked that the extended study of the rocks in the
central portions of the area has shown that, while dikes may perhaps have
penetrated to the lower parts of the section, there is no evidence afforded
by the bare rock surfaces, or by the materials of the drift so far as observed,
which would lead to the supposition that these injections penetrated into
the zone of the upper conglomerates.
Perhaps the most interesting group of what appear to be intrusive
masses is that of the pegmatites which occur in the southern portion of the
western margin. As we go southward from Providence there is a gradual
increase in the measure of metamorphism to which the Carboniferous
strata have been exposed. The observer is led to suspect the existence of
some extensive concealed intrusion which has applied much heat to the
section. These indications of metamorphism increase until they attain their
maximum in the portions of the field in and about Boston Neck and Tower
Hill. Where the alteration of the strata is most considerable— where,
indeed, those beds appear as ordinary gneisses — we find extensive pegma-
tite intrusions, which penetrate these conglomerate and sandstone gneisses.
1 have been unable to determine whether these intrusions are to be classed
as dikes or as veins. So far as observed, the facts hardly warrant the
assumption that the metamorphism is directly due to the incoming of the
DIKE ROCKS OF THE BASIN. 29
pegmatites, biit rather lead to the supposition that these last-named deposits
have been derived from some large granitic mass intruded into the basement
rocks of the section, though at no point exposed on the surface.
The facies of the beds in the region about North Attleboro makes it
appear not unlikely that volcanic action may have taken place in this por-
tion of the held. •
CHAPTER II.
PHYSICAL HISTORY OF THE BASIN.
RELATION TO MARIIVE AND ATMOSPHERIC EROSION AND DEPOSITION.
It may well be noted that tlie degree to which shore land basms, such
as we are now considering, are developed is in general determined by the
amount of time during which a given coast line has remained in about the
same position. It is not to be supposed that the coast level remains endur-
iugly the same, but rather that in the repeated oscillations the sea does not
long desert a given field. During the periods when the area is relatively
high the rivers in the lower part of their courses have a chance to develop
those wide valleys of gentle slope which are characteristic of regions that
have attained very nearly to the general base-level of erosion — i. e., the
average position of the sea during its endless variations in height. In
general it may be said that widi valleys next the shore are the best possible
indications of a relatively long continued preservation of coastal conditions
in the region where they appear. The Atlantic coast of the Americas
affords numerous examples of these broad, nearly base-level valleys, which
have been formed at divers times in its history. As the existence and the
number of these valleys have a distinct bearing on the problem in hand, it
is worth while to give a brief general account of them, at least so far as
North America is concerned.
Along the Gulf of Mexico there are half a dozen of these considerable
troughs, of which those of the Mississippi and Mobile rivers are the most
characteristic, or at least the best known. Both of these valleys, and
probably the other basins along this coast, are, at least as regards their lower
parts, of relatively modern origin, dating probably from Tertiary times.
On the Atlantic coast, to the north of Florida, there are again a number of
these lately formed basins, of which those of Albemarle Sound and Chesa-
peake and Delaware bays are the largest and most characteristic.
STEITCTUEAL DEPTH OF BASIN. 31
North of Delaware Bay, and thence along the coast to Greenland, the
number of distinct coast erosion troughs increases and the evidence of their
great antiquity is very clear. The position of the Newark deposits in the
Connecticut Valley makes it evident that this region was an eroded basin
as far back as the Triassic period. The Narragausett Basin owes its
excavation to actions which antedate the Carboniferous. The Boston
Basin, and several others to the northward along the shores of Maine, may
be dated back to the Paleozoic age. Yet farther northward, wide valleys
of the coastal-plain type, though now deeply submerged, are indicated by
the reentrants of the Bay of Fundy, the Gulf of St. Lawrence, and prob-
ably by the great system of embayments of the Arctic realm, the Greenland
Straits and Hudson Bay, as well as by a host of lesser indentations, which
probably mark the seat of long-continued or, rather, frequently repeated
river action interrupted by periods of marine invasion.
It will be observed from the statements made in this report that the
Narragansett Basin has at present an average structural dejith of probably
not less than 7,000 feet and a maximum depth of 12,000 feet; that is to
say, the downfolded Carboniferous rocks and the beds which lie beneath
them attain, at the base of this incline, a position at least the last-named
distance below the present sea level. The question arises as to how much of
this geological depth is due to erosive work on the rocks of the area and
how much to actual depression preceding or connected with the folding of
the strata. If the basin originally had anything like its present depth, we
should have to suppose a very great change in the position of the coast
line. If, on the other hand, we may assume, as is done in this paper, that
the basin, as regards its geologic depth, is mainly the product of folding,
and that the movements are probably due in the main to the accumidations
of deposits, then the original depth of the basin may have been slight.
The evidence seems to show that the coastal basins of the Atlantic
shore owe their depth to three more or less associated actions — to river
ei'osion, to downflexing and faulting associated with the accumulation of
strata during periods of subsidence, and to the massive swing of the conti-
nent in those large deformations such as have taken place in recent times,
with the consequent invasion of the sea into the valleys. Two of these
actions are local in their nature; the third involves continental or perhaps
wider conditions.
32 GEOLOGY OF THE NAREAGANSETT BASIN.
It should be said that the mainspring of the development which has
taken place in these basins is the crustal strain which manifests itself in
mountain building. Where this strain, as in the ordinary conditions of
mountain growth, such as existed in the West Appalachians, takes effect
on uniform, horizontal, little eroded strata, the action appears to result in
the formation of elongated, more or less accurately parallel ridges, such as
are exhibited in the Jura or the Alleghenies. Where, on the other hand,
as along the Atlantic coast, the crust is composed of ancient massive rocks
in which deep valleys have been excavated, the orogenic strains result in
the deformation of the patches of stratified rocks which may have been
accumulated in the great valleys during the periods of subsidence.
The dislocations of the Atlantic coast basins clearly indicate that the
stress which has caused them was what we may term quaquaversal — that is
to say, it has acted in several directions around the greater part of the hori-
zontal circle. This behavior of the crustal stress is quite different from that
which we find exhibited in normal mountains; there, as before remarked, the
relief has been obtained by the formation of ridges and furrows, the axes
of which are nearly parallel to the same great circle. Although the amount
of this parallelism has usually been much exaggerated, there can be no doubt
as to its substantial existence. HoAvever, it seems unwarranted to suppose
that the axial relation of the ridges is due to the existence of a strain acting
in but one direction. All that is required to produce the result is either a
certain predominance in the value of the strain in a particular versant, or,
what comes to the same thing, a greater tendency to yield along one set of
lines. Instances of this may frequently be seen in the wrinkling of veneers
or in sidewalks which have been covered with some plastic materials. With
a simple device the cream on a pan of milk may be made to show the
effects of the same general principle, where the giving way takes place
rectilinearly, though the difference in pressure in the several axes of the
circle is but small. Moreover, even in the most nearly parallel mountains,
there are generally to be found cross folds which show very clearly that
the strain has not been uniaxial.
The foregoing considerations lead us to infer that the diversity of axes
in the elevations produced in the singular group of antecedent basin folds
which we are considering has not been brought about by a class of strains
dififeriuo- as resrards their distribution from those involved in the formation
VARIATIOXS OF SEA LEVEL. 33
of ordinai-y mountains, but rather through the opportunit}^ which these
diversely shaped and irregularly disposed basins have afforded for the ^-aried
application of the stresses.
As before noted, thS evidence derived from the geological history of
southeastern Massachusetts and the neighboring portions of the shore to
the north\\^ard as far as the Grulf of St. Lawrence, and to the southward
into tlie Carolinas, shows that while this coast line has been subjected to
repeated and considerable variations of level, it manifests an equally clear
tendency to return to about its original position. Beginning with the
Cambrian time, we find reason to believe that this region was coastal at the
outset of the Olenellus epoch. If the rocks of the Roxbury conglomerate
be of the Potsdam period, the same was true at the last of the Cambrian
stages. It is again the case in the Carboniferous, in the Trias, the lower
Cretaceous, the middle Tertiar}-, and at the present day. Evidence found on
the coast of Maine indicates that the coast in that part of the field was also
near by in the Devonian period. Thus, in eight or nine of the great periods,
well spaced through recorded geological time, we find the coast of this dis-
trict near to its present attitude. As the action of erosion during the periods
of elevation, and the accidental burial beneath later deposits of portions of
the strata, are likely to have obliterated much of the record, the point which
we are endeavoring to make appears to be well affirmed. This point is of
evident value in the present inquirv, for it serves to show a reason why
extensive erosion valleys are characteristic of the Atlantic coast. In those
phases of the coastal movement in which the land has been above the
present level of the sea, there has been an opportunity' for the formation of
extensive valleys of erosion, which, from time to time, with the downsinking
of the shore line as a whole and the downward warping, concomitant with .
the extensive deposition, have had a chance to take on their present peculiar
character.
In this connection it should be noted that the usual tendency of shore-
line changes on the periphery of the continental fold is to return the coast
after each considerable oscillation to somewhere near where it was before.
Elsewhere, more than once, I have called attention to tlie facts that within
the ordinary growth of the great corrugations on the earth's surface the
movements are normally those of downsinking of the ocean floors and
uprising of the emerged portions of the continental mass, and that this
MON xxxiii 3
34 GEOLOGY OF THE NAEEAGANSETT BASHST.
movement is essentially like the rotation of the levei* about the neutral or
fulcrum point, which is ordinarily near the shore line. On the doctrine of
probability, it is more likely to fall at the contact of land and sea than at
any other point in the length of the rotating are'a. If the land advances
from the ancient shore, the natiiral result is an increase in the amount of
erosion and consequently of deposition off the given coast line. This, in
turn, as an effect of the loading, tends more sharply to depress the region
next the coast, and so, in time, to a return of the shore toward its original
position. If, on the other hand, the sea invades the land, considerably
narrowing the field of erosion, the supply of sediments is checked and the
element of accumulating' weight which makes against the uprising is
proportionately lessened, with the resulting tendency of the district to
ascend in the next adjustment of the crustal stresses which are involved in
continental growth.
So far as I am aware, the mountainous elevations which have been
formed along the Atlantic coast appear to have been the result of stresses
which have acted in a somewhat continuous manner from the Cambi'ian to
near the present day. The di.slocations seem to have occurred in these
basins as early as the first-named time, and in the basin of Marthas Vine-
yard they operated perhaps until the first stages of the last Glacial epoch.
It is true that the evidence as to the distinct basin-like position in which
the rocks of Marthas Vineyard lie is not very clear, for the reason that the
eastern wall, if such wall existed, is now below the level of the sea; but
the mountain-building nature of the disturbances appears to be unquestion-
able, the original folds having had a geological height of several hundred
feet, though, owing to the soft nature of the strata, they have now been
reduced to near their base-levels.
It is a notable fact that in these erosion-basin mountains of the Atlantic
coast there is a manifest tendency of the streams to return again and again
to somewhere near the paths from which thejT- have been displaced by the
subsidence of the areas beneath the sea or by the corrugation of the beds
which were formed during these periods of depression. Thus in the case
of the basins along the coast of Maine, those of Boston, the Connecticut,
and the set about the Chesapeake, streams answering to the original agents
of erosion now occupy their ancient sites. It is evident that in this
particular, as in many other features, the dislocation areas we are consider-
ORIGIN OF SEDIMENTS. 35
iug differ from those of normal moimtains. In the last-named group, as
has been often remarked, the sti'eams very generally come to occupy
the geological highlands — the crests of the anticlines. The reason of the
departure from the general rule in these antecedent basin mountains is that
in them the rim is of hard rock, while the central portion of the area con-
tains softer materials.
It should furthermore be noted that the downsinkings which lowered
these valleys, and thus afforded the opportunity for deposition, were not
generally so extensive as to induce the formation of normal marine deposits.
After the beginning of the Carboniferous, indeed, it ma}^ be doubted whether
the submergence beneath the level of the sea was, until Cretaceous times,
ever great enough to mantle far over the surface of the country. Apart
from the local downsinkings, I see no reason to believe that the shore
within this time has swayed downward or upward more than a few hundred
feet.
So far as the examination has been carried, the seat of origin of the
detrital materials contained in the Narragansett Basin is tolei'ably well
explained. The granitic, trappean, schistose, and other rocks represented
in the conglomerates, with a single exception, may be paralleled from
deposits the like of which are known within a few miles of the margin of
the basin. The exception — a most notable one — is in the case of certain
quartzite pebbles, sometimes containing an abundance of ill-preserved
brachiopods. These quartzites are all fine grained, hardened, but not
greatly metamorphosed, and of a hue varying from blue to white. The
age of the material, as determined by Walcott, is that of the Potsdam
sandstone.
Pebbles of these quartzites plentifully occur in the upper conglomerates
of the Narragansett series, as is elsewhere noted in this memoir. They are,
however, best known from their occurrence in the drift deposits, where their
presence is doubtless to be explained by the breaking up of the Carbon-
iferous beds in which they formerly lay. On the northern shore of Marthas
Vineyard they can readily be gathered to the number of many thousands,
and on Cape Cod they occur less plentifully as far east as Highland Light.
As the pebbles, so far as observed, are always small, never exceed-
ing about a foot in diameter, and as they are always rounded in a sub-
spherical form, it seems clear that none of them have been brought into
3(3 geoloCtY of the is^aeragansett basin.
their present position from the original strata by the action of the last ice
period. Forming, as the)' do, a considerable part of the mass of conglom-
erates in the Narragansett Basin, it is clear that they were derived from an
extensive field. Their condition indicates that they were imported from
that field by torrent action. Although it is possible that these quartzite
deposits originally lay over the country to the westward of the Narragansett
Basin, the failure of the beds to appear round the periphery of that area
leads to the supposition that the district whence they were derived lay to
the eastward of the trough, perhaps beneath the region now covered by the
sea This supposition receives some warrant from the fact that these peb-
bles are most abundant in the eastern portion of the basin, while they seem
to be almost lacking in the western part. The existence of these pebbles
well toward the extremity of Cape Cod appears to indicate the occurrence
of similar deposits beneath the waters of ^Massachusetts Baj. For further
details concerning the origin of these quartzite pebbles, see Part II, by
Mr. Woodworth.
AGE OF THE CAKBONIFEr^OUS ROCKS OF THE BASIN.
The evidence goes to show that from the earliest stages of the Pale-
ozoic to the beginning of the era when the Carboniferous beds of this
district began to be laid down the field was mainly, if not altogether, the
seat of erosive actions. No remnants of the formations between the lower
Cambrian and the Carboniferous have been found in folds which exist in
the basement rocks of this part of the countr}^ The fact that beds of
Cambrian age have survived at several points in the Narragansett Basin in
the region to the northward, while no deposits of the Silurian or Devonian
horizons have been identified, leads to the supposition that the sediment-
making conditions were not in existence at the time these beds might
have been laid down. The researches of Lescpiereux, a digest of which is
given by Woodworth in Part II, make it eminenth' probable that the
Carboniferous series of this field does not begin with the lower portion of
the Coal Measures, but with the upper part of that section. Not onl}^ are
the lower limestones and the Millstone grit lacking, but about half of the
measures which normally contain a better coal in the district west of
the central Appalachian axis are also lacking.
It should be observed that the fossils Avhich afforded the basis for
SEPAEATIOX FROM THE SEA. 37
Lesquereux's conclusions were obtained from beds whicli lie at 2,000 to
3,000 feet above the base of the Coal Measures as f(iund in this basin,
and that the beds whence his fossils were obtained do not extend nearer
than 2,000 to 4,000 feet to the top of the highest remaining beds of
Carboniferous age which are found in this area. It is of course possible
that the lower portions of the section, the fossils of which have not yet
been studied, may prove to belong to the lower Coal Measures, but the
essential lithological similarity of the beds below the upper cong'lomerates
makes this view improbable. So, too, the lack of paleontological evidence
concerning the precise age of the upper conglomerates permits the suppo-
sition that they may belong to the Permian period.
ORIGI^fAXi REL,ATIOK OF THE NARRAGAXSETT BASIX TO THE SEA.
It is noteworth}^ that no trace of marine fossils has been found in any
portion of the Carboniferous section in this basin. ]\Ioreover, there are no
limestone pebbles which would lead to the suspicion that beds of this origin
had ever formed a part of the original sections. A few limy deposits which
occur in the northwest portion of the area appear to be the results of infiltra-
tion, and to be classable as veins. When we consider that the Carboniferous
section of the West Appalachians exhibits evidence of frequent intrusions of
the sea, the question arises how a basin having the stratigraphical profundity
of that of Narragansett Bay could have been developed adjacent to the
shore line without having', in its repeated subsidences, experienced marine
invasion. At the present time the bottom of this basin lies several thousand
feet below the plane of the ocean waters which penetrate it. Even befo]'e
the mountain-building movements which have deformed the rocks began,
it is probable that the basin had something like its present depth.
The conditions of the basin, as above noted, lead to the conclusion that
during the Carboniferous period it was continuously separated from the sea,
and therefore had the character of a lake, or perhaps that of a broad river
valley. As it was evidently the seat of very considerable drainage, the out-
going water might have excluded, in a sufficiently effective way, the pene-
tration of the oceanic waters, even though the plane of deposition was laot
much above the marine level. When, however, we consider how subject
all coast lines appear always to have been to oscillations of level, it seems
most reasonable to suppose that the basin lay always at a considerable
38 GEOLOGY OF THE NAERAGANSETT BASIK
height above the coast hne, and most hkely at some distance inland from it.
These considerations serve to support the hypothesis, which is suggested by
many other features of the Atlantic shore line of North America, that the
shore line in later Paleozoic time lay farther east than it does at present.
ORIGIIS AL DISTRIBUTIOIV OF THE EAST APPALACHIAjV COAL FIELD.
The distribution of the Carboniferous strata with reference to the main
axis of the Appalachian system affords some valuable information as to the
movements and attitudes of the continent during the later stages of Paleo-
zoic and the earlier stages of Mesozoic time. It is noteworthy that, while
the Carboniferous of the West Appalachians extends to the southward
until the beds pass beneath the Cretaceous and Tertiary deposits which lie
to the north of the Gulf of Mexico, rocks of that age are wanting along the
Atlantic coast until we attain the latitude of northern Connecticut and
southern Massachusetts. Thence to northern Newfoundland accumulations
of this age occur, though in detached basins which were evidently formed
as somewhat separate areas. The uniform absence of Carboniferoits deposits,
and indeed of the Paleozoic beds above the Silurian horizon, along the
southern portion of the Atlantic coast line of the United States, clearly indi-
cates the long continuance of this part of the continent in the emerged state,
a state which appears to have continued in the southern section to Triassic
time, and perhaps to the Newark division of that age. If Coal Measures
strata had been deposited on this part of the Atlantic coast above the pres-
ent sea level, it is hardly to be believed that considerable remnants would
not have remained in the Dan River, Richmond, and other basins. The
natural conclusion is that these beds were not laid down, but that the shore
from the Hudson southward remained in the elevated state, and that in this
field Carboniferous strata were not accumulated, while farther north the
conditions so favored this work of deposition within the region about the
mouth of the St. Lawrence that the sections of this stratigraphical division
are on the average thicker than they are in the West Appalachian field.
With the advent of the Triassic epoch the whole coast line appears to
have been lowered, so that the beds of this age probably formed a more or
less continuous sheet from South Carolina to Nova Scotia.
In the Carboniferous downsinking of the eastern shore the conditions
which brought about the formation of the Coal Measures do not seem to
have extended as far south as the valley of the Connecticut. The pre-
ATLANTIC COAST BASINS. 39
sumption that this trough is old, and that in the Carboniferous period, if it
had been sufficiently low lying, it would have afforded a favorable field
for the accumulation of strata, is supported by the fact that Helderberg
strata are found within its bounds, and the absence of the later Paleozoic
is fair proof that the trough was so placed that it remained subjected to
erosion. In this connection it is interesting to note that the Triassic
period does not appear to have introduced true marine conditions along
this coast line. The fossils indicate that the beds were formed either m
fresh-water lakes or in estuaries. So, too, the Carboniferous strata of the
East Appalachian district contain only fresh-water fossils, notably lacking
the thin beds containing marine fossils which in the West Appalachian
district clearly indicate successive invasions of the sea. These facts are
best explicable on the supposition that the Atlantic coast in this part of its
history lay farther to the east than it does at present, and that all the beds
from the beginning of the Carboniferous upward through the greater por-
tion of the Triassic section were formed in basins so far separated from the
sea that no marine life found access to them.
The development of fresh-water basins on the Atlantic coast in the Car-
boniferous period has perhaps its parallel on a larger scale in that curious
formation of shallow lakes which occurred in Cretaceous time along the
eastern border of the Cordillex-as of North America, and which gave during
the Mesozoic and a part of Tertiary time the nearly continuous fresh-water
areas from Texas to the high North. Depressions of this nature appear to
be of common occurrence along the bases of mountain ranges which have
recently been subjected to extensive movements. It seems possible, indeed,
that they are due to counterthrust action, which tends to bear down the
part of the earth immediately outside of the field of considerable elevation.
Phenomena of this sort are traceable not only in this country, but around
the margin of the Alps and other mountain districts which have been suffi-
ciently well mapped to give indications of these old basins. On this suppo-
sition we can account for the general tendency of the East Appalachian
district to subside during the time when the neighboring ranges were under-
going elevation. The intensification of this subsidence at particular points
and the conseqiient infolding of strata, which have thus been preserved from
erosion, is to be explained through the accumulation of thick deposits of
unconsolidated rocks in preexisting erosion troughs.
40 GEOLOGY OF THE NAREAGANSETT BASIN.
AIS^CIENT MARGIN OF THE BASIX.
The original extension of the Carboniferous beds the remains of
which are found in the Narragansett Basin can not be determined. The
e^adence goes to show that in the process of filhng the trough the margin
of the iield in which the deposits were accumulated extended in a somewliat
continuous manner in every direction, this extension being in a way coin-
cident with the 2:)rogressive subsidence of the area. There must thus have
been a succession of shore lines, each lying farther away from what is now
the central portion of the field. It is probable that the arkose deposits which
are now found around a large part of the margin of the existing Carbon-
iferous area were accumulated at no great distance froni what was the shore
line at the time the}' were formed; but the later shore, answering in age to
the upper conglomerate, may have been some scores of miles beyond the
present limits of the Carboniferous rocks, the materials being brought in
over the shelf of earlier-formed deposits. The fact before adverted to, that
the fossil-bearing quartzite pebbles come from some unknown and possibly
rather remote district, indicates the validity of this hypothesis.
Although the Carboniferous section of this basin is thick, the fact that
the conditions favored the formation of rapidly accumulating conglomerates
of itself suggests that some portion of the section has been worn away
The fact that no higher-lying beds than the Carboniferous exist in this por-
tion of New England, although there is abundant evidence that a large
amount of erosion has taken place since the time of the Coal Measures, is
also evidence that a considerable thickness of stratified rocks must have
disappeared from this field. The margin of these vanished formations
must have been far beyond the limits of the Narragansett Basin.
RELATIVE EROSIOK OF EAST A^s^D WEST APPAEACHIAlSrS.
It requires but a glance at the topography of the districts l}'ing to the
east and to the west of the ancient or mid-Appalachian field to show
the observer that there has been a great difference in their erosional history.
On the west we find the mountain folds on the whole well preserved as
regards both their anticlinal and their synclinal elements, the average pres-
ervation of the structural features being more perfect than that of any
other equallv well-known great mountains, except, it may be, portions of
AGE OF DISLOCATIONS. 41
the Jura. In most cases the crests of the anticHnes have been widely
opened by erosive processes, and in some rare instances the destruction has
advanced so far that the synchnal element in the foldings has come to lie
farther above the neighboring drainag-e than the existing crests of the
upfolds. Notwithstanding this excessive local downweai'ing which has here
and there taken place, the West Appalachians have everywhere, except in
their extreme southern part, retained a striking topographical relief. It is
indeed easy to see, even in the most ruiiied part of these great geological
edifices, the plan of the structure and the g-eneral features of their archi-
tecture. It is quite otherwise with the related elevations of the Atlantic
coast. As before noted, the East Appalachians have, in their topographical
expression, scarcely a semblance of the structure of the West Appalachians.
In fact, their lack of relief has to this day hidden from geologists their real
importance as orogenic phenomena.
Between Greorgia and the Bay of Fundy none of these mountains have
any distinct topographical relief. Here and there the crystalline rock which
were formed under their anticlines, or the massive outbreaks of igneous
rocks which took place during the folding, remain as considerable hills, or
in the case of the Mount Desert elevations the}^ may attain the height of
1,000 feet or more; but in the Narragansett Basin, although the folds cer-
tainly have a geological relief of not less than 10,000 feet, the actual differ-
ences in altitude from the depth of the present water channels to the highest
elevations does not exceed 500 feet. If these mountains of the East
Appalachians had been no more worn down than the Alleghenies, they
would afford the most majestic elevations in the eastern part of the continent,
instead of having no distinct value in respect of topographical relief
It might at first be supposed that the age of these eastern reliefs is
greater than that of the western dislocations; the evidence, however, points
to the conclusion that, while some part of the dislocations may be due to
stresses which were of Cambrian or Silurian age, the greater of these
accidents date from post-Carb(niiferous times, and are probably to be
assigned to the age of the Trias or the Jura. The disturbances which have
contorted the Cretaceous or Tertiary rocks of Marthas Vineyard clearly
indicate that the orogenic forces have acted along the Atlantic coast with
much energy down to very modern time. To what, then, can we attribute
the very great differences in the relief of these two mountain-built districts?
42 GEOLOGY OF THE XARRAGANSETT BASHS^.
The modern school of topographical geologists is disposed to explain
such differences as those which we are considering hj the supposition that
the region of less relief — the eastern — has been long base-leveled, without
the refreshment of its relief which is induced by a subsequent process of
reelevation; while the western district, having been once, or perhaps more
than once, worn down to near the ultimate erosion plane, was lifted again
to a height which permitted the machinery of its torrents to sculpture new
reliefs. In favor of this supposition there is the fact that the summit levels
of many peaks in the West Appalachians are so nearly in one plane that it
is not unreasonable to suppose, as a working hypothesis, that the valleys
have worn down from an ancient base-level. To this suggestion it may be
answered that, so far as the evidence goes, there is reason to believe that
the eastern shore has shared in these upward movements. The Berkshire
Hills shoAv, by the coincident levels of their summits, as distinct a trace
of base-level as do the Alleghenies. Moreover, in ,the immediate vicinity
of the Narragansett Basin the broad ridges of the Worcester axis carry its
levels to about 1,000 feet. Yet it is plain that this set of folds owes its
origin to the same movements that developed those of the Bay district. In
a word, even if we allow that uplift after base-leveling in the one case and
lack of the upward movement in the other might account for the very great
difference in conditions, we have not the means to verify the hypothesis; it
therefore has no apparent value to us in interpreting this field.
Although I regard the considerations which are commonly included
under the title of "base-leveling" as one of the most important conti'ibutions
to physiographical geology, it seems to me that we must guard against the
danger of inferring too much concerning the existence of ancient leveling
of the land down to near the plane of the sea from the seeming- accords in
the altitudes of mountain summits. It is easy to see that this accord is only
of a very general nature, it being necessary in the classification to allow a
range of elevation amounting to several hundred feet. It may well be that,
beginning with the utmost diversity which could have existed in the heights
of the Alleghenies, the pi'ocess of downwearing might have bi'ought about
as near an approach to uniformity of height as actually exists in the peaks
of that range. So long as the rocks are of like hardness and the folds of
like size, the tendency would be to keep the downwearing crests at some-
where near the same level.
CONTINENTAL SHELF. 43
Another reason for the disappearance of the topographical rehef of the
East Appalachians can be found in the marine erosion to which they have
been subjected. As before remarked, it is evident that the Atlantic coast of
this continent has for a very long time been in about its present relations
to the sea. It is characteristically an old shore, and has the marks of age
in the broad continental shelf which fringes it on the east and in the wide
belt of lowlands which lies to the landward of the coast line. These two
features seem to be closely related to each other; the submarine shelf
probably represents in good part the accumulations of d(ibris which has
been worn from the bench which the sea has cut into the. land.
Because it is covered by the sea, w^e can determine but little of the
continental shelf, except by inference from what we reasonablv take to be
an emerged part of its mass as it appears in the structure of the great
southern coastal plain, that plain land being evidently composed of conti-
nental waste in part removed by marine action, together with the ddbris of
organic forms; biit of the bench we may know much, for the greater part
of it is above the sea level. If the student would appreciate the importance
of this seaboard bench on the Atlantic coast of the United States, he should
study the section from the great Appalachian Valley to the sea. Probably
the most instructive section is from the region of the upper Shenandoah to
the region about Fort Monroe, in Virginia. It is readily noted that the
crystalline rocks on the western side of the Blue Ridge rise steeply
from the broad vale which is occupied by the Cambrian beds. On this
side of the ridge there is no trace of benching ; the mountain sides show the
ordinary torrent slopes. On the eastern side of the ridge, however, there
lies the extensive rolling country commonly known as the "Piedmont
Plateau," which has been recognized as a jjeculiar feature in the section
from New Jersey to Georgia ever since the country was occupied by the
Europeans. This region has peculiarities of soil and of surface aspect
which are due to the fact that it is to a great extent underlain by crystalline
or metamorphosed rocks essentially like the complex which makes the
higher country of the Blue Ridge. When the rocks exhibit bedding, the
attitudes of the strata indicate highly compressed mountain folds. The
topography of the district shows much torrent cutting on the surface of a
sloping bench which declined toward the sea at the rate of 10 or 20 feet
to the mile, the upper or northern margin of this bench passing rather
suddenly into the steep slopes of the mountain ranges.
44 GEOLOGY OF THE ISTAERAGAIN^SETT BASIX.
The coiiditioDS of the surface are in the main as shown in PL I, with
the exception that occasional outliers of high land are found over the
Piedmont district. These outliers have the g-eneral aspect of ancient
islands, the bases of which have of late been elevated above the sea
level.
Perhaps the best instance of these structures is afforded by King-
Mountain, North Carolina, which, as has recently been sll0^vn hj the studies
of Prof Collier Cobb, of the University of North Carolina, is an insular
mass which has by elevation been embodied in the area of the emerged
continent.
It should be said that this bench, with local variations, extends along
the Atlantic coast of the continent as far north as the St. Lawrence district,
but that the ancient islands are nowhere so well shown as in the Cai-oliuian
section.
The foregoing statements will make plain the working hypothesis as
to the erosion of the East Appalachian reliefs. We see that these moun-
tains lie in the realm of the marine bench, that border land of the continent,
where the repeated up and down goings of the sea bring the machinery of
the surf and the other erosive agents of the coast line — the frost, the tides,
and the winds — to bear in succession on every part of the surface. In
recent years there has been a disposition to deny to marine action any
considerable effect on the topography of a country. This limited view
is a natural recoil from the old notion that the sea is the principal agent
in land carving. From overestimating the value of a natural agent, the
inevitable step is toward an underreckoning, which seems in this case to
have gone altogether too far. A part of the misestimation as to the ero-
sional value of tlie shore agents is due to the study of coastal processes in
what we may term adjusted shore lines, such as are to be found where the
sea has acted for a long- time on a coast where the lands have not altered
in their position with reference to the sea. In such conditions the sea, by
a complicated system of actions, builds a series of obstructions in the way
of shallows and beaches, which serve to bar the land from its assault, and
which often cause the energy of the waves and tide to be expended in such
wise as little if at all to erode the laud. Wherever we are able to study the
action of the sea where the land is rapidly oscillating, we note at once the
great increase in the effectiveness of the ocean's work. Thus, on the coast of
EFFECTS OF CHANGES OF LEVEL. 45
New Jersey, where the subsidence is at the rate of perhaps 2 feet in a cen-
tury, the formation of the usual sand barrier beaches is prevented for a
considerable section, with the result that the sea, save for the interference
of man, works back into the cliffs at the rate of several feet in a 5^ear.
While a process of subsidence is in general favorable to marine erosion,
that of elevation is probably yet more advantageous to the wave and cur-
rent work; and this for the following reasons. When the land sinks, the
debris due to the surf remains in the possession of the sea and may be
used to build barrier beaches at a higher level. Off the coast of North
Carolina, where there is also a subsidence movement, because the amoiuit
of sand is large, the beaches are still effective walls against the sea.
When the land rises, however, the beach material is constantly left behind
in the elevated coast lines, and at each successive zone of attack the sea
assails an unmasked shore. At present we appear to be in a period where
the land oscillations are relatively very slight; we therefore are in a posi-
tion where we would naturally underestimate the true measure of marine
erosion. Still, taken in a large way, we can easily see that the coastal
erosion is by far the most effective at the times, which we know to be fre-
quent, when the shore is moving upward or downward. This shoreward-
sloping bench may be taken as the result of the two main varieties of land
Avearing— that due to the natural work of the rainfall, and that due mainh" to
the sti-oke of the waves as they break upon the coast. In the equation which
determines the slope of the coastal bench, we have to reckon the effect
of many agents and conditions. Among these, the successive changes of
the base-level— i. e., the plane of the sea — are obviously of great importance.
As the surface of the bench gains in height, the capacity of the marine
agents become relatively diminished, for the reason that the marine cliff
grows higher and the waves have more deportation to effect for each unit
of the extension of the scarf into the land. On the other hand, with the
gain in height there comes a proportional gain in the wearing power of the
rain water, the capacity of which to do wearing work is directly rehxted to
the height above the sea at which it comes upon the land.
Although the conditions which are no\v found on the Atlantic coast of
the countr}^ are clearly less favorable to erosion than the average, it is evi-
dent to the attentive observer that the amount of marine erosion which is
now done along the coast from Cape Hatteras to Canada equals if it
46 GEOLOGY OF THE NAREAGANSETT BASIK
does not exceed in volume that which is accomplished by all the rivers
which empty into the sea along this part of the shore. We may say, indeed,
that the evidence, when fairly considered, leads ns to the conclusion that
the destruction of the reliefs in the Atlantic coast mountains — the East
Appalachians, as we have termed them — has been in a large measure due
to the long-continued action of the sea on the zone in which they lie.
In the case of the Narragansett Basin it seems impossible to account
for the destruction of the original reliefs by the action of water on its way
to the sea. If we take account of the existing water-filled troughs, the arms
of the sea, and the rivers, we find a plain cut by relatively wide and shal-
low canyons, which are now to a great extent filled with drift. This plain
is underlain by rocks of very diverse hardness, so that if its surface were
due to the result of the downwearing action of streams it should he most
irregularly carved, in place of having that shorn-off' aspect which the
horizontally delivered stroke of the waves produces. Therefore we may
conclude that the difference between the reliefs of the East and the West
Appalachians requires us to consider the benching' action of the sea along- with
the base-leveling process effected by rivers. Undoubtedly this latter base-
leveling action has to be reckoned, but only as one, possibly the least,
important element in the action. It may be noted, in order to complete
this interesting storv, that the greater part of the West Appalachians Avas
fully protected ag'ainst the action of the Atlantic by the rampart of the
Blue Ridge. It is a .corroboration of the h}"pothesis that at the southern
end of the A¥est Appalachians, where these mountains were exposed to the
action of the waves of the Gulf of Mexico probably at least until the end
of the Cretaceous or the middle of the Tertiary period, the mountains show
a measure of erosive action hardly less than that which is exhibited by the
worn-down ridges of the Atlantic seaboard
Some further considei'ation of the question as to the wearing down of
the rocks of this basin will be found in the next chapter, on the glacial
history of the field.
RECENT CHAXGES OF LEVEL.
It may be well in this connection to note the facts concerning' the
recent changes of level in the Narragansett Basin. As elsewhere remarked,
the evidence goes to sIioaa' that the amount oi glacial wearing, or at least
EFFECTS OF WAVE ACTION. 47
that of the last ice epoch, on this field was limited. We may therefore
assume, what is inferred from other evidence, that the drainage of the
district is substantially the same as it was before the last ad^'ent of the
glaciers. The drainage consists of sundry deep channels, the arms of
Narragansett Bay and their continuations in the narrowed rivers. To
explain these stream beds, we must assume that the surface of the country
was considerably higher during the preglacial time than it is at the present
day. If, as is probably the case, the central part of the bottom of Nar-
ragansett Bay is filled in with mud to the depth of 100 feet or more, as is
the case with other channels of like character on this part of the coast,
theu the recent subsidence may exceed 300 feet. A like process of reason-
ing applied to other parts of the shore between the Delaware and tlie St.
Lawrence leads to approximately the same conclusion as to the amount in
which the sea has gained on the land. It should be said, however, that this
change in the position of the shore may be due to an alteration in the level
of the sea itself quite as well as to the lowering of the land in this jjart ol
the shore; in fact, the extent of this modern invasion of the land by the
sea along nearly all the shores of the continents raises the presumi^tion that
the action may have been due to a vast movement of the floor in some part
of the ocean realm.
GEXERAt, STATEMEXT COXCERXHSTG BASE-LEVELIKG.
What has Ijeen said in the preceding pages concerning the relations of
marine and laud denudation makes it desirable to assemble the considerations
which bear upon this problem.
There can be no question as to the importance of the base-leveling-
theory, which assigns to the atmospheric agents of erosion the downwearing
of the land masses. It should be noted, however, that the marine agents —
the cutting action of tlie waves and the marine currents dependent on wind
and tidal work — have in their appropriate place a certain amount of influ-
ence. It should also be noted that as the land is worn down toward the
level of the sea the efficiency of the atmospheric forces in the work of
further reduction continually diminishes, because of the lessened fall of the
streams and from the tendency of the surface to become deeply covered
with a protecting detrital envelope.
In the low levels of the land, where the aerial ao-ents become less
48 GEOLOGY OF THE NAREAGANSETT BASIN.
effective, we may always expect to find some effect arising from the repeated
visitations of the sea brought about by the ahnost continual oscillations in '
the height of tlie land. The measure of this marine work is commonly the
greater the nearer we attain to the average level about which the sea has
oscillated for a considerable time. Thus marine action comes in to sup-
plement that of the atmosphere.
Along the coast of New England, and particularly in the district con-
sidered in this report, within the limits of the recent oscillations of marine
level, we find at man}'- points evidence that the sea at higher stations than
now worked to remove the coating of detritus and to expose large areas
of the surface to the process of decay, which rapidly tends to break up the
rocks. This part of the marine work, in favoring erosion, is perhaps of as
much consequence as that due to the direct cutting action of the sea.
It may be remarked that the frequent invasions of the sea, by producing
plains of detrital material, such as those which exist in the southern part of
the United States, tend also to reduce the surface of the land to an
approximately level form. Thus the evidence goes to show that beneath
the southern plain the contour of the ancient rocks is irregular, they having
been mantled over by a thick coating of debris accumulated along the
continental shelf We therefore see that the ocean tends in two diverse
ways to bring about coastal plains — first, by aiding in wearing down origi-
nally irregular surfaces to a level attitude; and secondly, by constructing
detrital plains over those surfaces winch in part have thus been brought to
a nearly horizontal attitude.
As for the oscillations of the land which serve to bring the mill of the
surf at various levels over its surface, it may be said that since the Carbon-
iferous period tiiere is evidence of many such swingings, which have brought
the plane of the sea from a few score to several hundred feet above its
present position on the Atlantic base of the continent. The evidence to
the same effect from other regions is so extensive that it may be called a
world-Avide phenomenon. It may safely be assumed that coast lines are
normall}^ instable, and this through a range of several hundred feet.
As to the amount of cutting which can be effected by the sea in pro-
portion to that which may be accomplished by the descent of waters from
a high level to the shore line, the facts are not yet sufficiently ascertained
to permit any definite statement. It may be said, however, that where the
exposure is such that the waves may assault the shore with considerable
SUCCESSIONS OF DEPOSITION, 49
energy, especially where the tides are high, the erosion, even in a brief period
of geological time, is often very great. Thus on the coast of Yorkshire, north
and south of Whitby, the marine clitfs, apparently formed in the brief
period during which the sea along that coast has had its present attitude,
have an average height of several hundred feet, and the platform which
marks the lower range of wave action extends on the average a mile or
more from the shore. The prism of rock removed by this cutting is in
mass greater than we can well assume to have been eroded from the land dur-
ing the same period for the distance of 20 or 30 miles from the coast line.
Along the shore of New England, though the coast generally lies against
rocks of more than usual hardness, the benching action of the sea is almost
always noticeable. In the few thousand years during which this coast line
has remained at its present attitude, the amount of erosion has apparently
been many times as great as over any equally extensive interior portion of
the field subject to the action of atmospheric agents. Considering only the
hard rocks, especially those of the coast of Maine, I am of the opinion that
the atmospheric erosion accomplished in New England since the Glacial
period has not been so great as that effected along the shore belt in the
much shorter time which has elapsed since those coasts began to be assaulted
by the sea.
It is to be observed that, in all estimates as to the relative value of
marine and atmospheric erosion, account must be taken of the dissolving
action of the land waters, which is always wanting in the case of the sea.
Although the interior erosion of New England is now exceedingly small,
the solutional decay is gradually, indeed it may be said somewhat rapidly,
advancing in certain portions of the glacial deposits, so that the time will
come when they may pass off with greater rapidity. Making allowance for
this and for other evident qualifications as to the relative value of marine
and interior erosion, it may still be said that the former agent has a certain
and important, though much neglected, influence in determining the shape
of the lower-lying portions of the land mass.
CYCliES OF DEPOSITIOI^.
Considerations as to the succession of phenomena of deposition which
were brought into view by the writings of the late Prof John S. Newberry
and others, appear to receive no support from the successions of strata in
HON xxxiir 4
50 GEOLOGY OF THE NARRAGANSETT BASIN.
the Narragansett Basiii. The first stage of deposition in this field, when
the formation of the Carboniferous section began, is marked by the occur-
rence of fragmental beds, mainly arkoses. Where the succession is well
displayed, these arkoses are followed by conglomerates of no great magni-
tude. Succeeding these with tolerable uniformity comes a section of several
thousand feet where the deposits are prevailingly rather fine grained. In
the ujDper half of the section there is a return to conglomerate-making-
conditions. This return appears to have been made rather suddenly.
At fii'st sight it seems reasonable to suppose that the succession of
events, as indicated in a general way by the section, gave (1) a period in
which the shore line was everywhere near to the margin of the present
basin, permitting the formation of arkose; (2) a period when a continued
depression kept the shore line always at a distance, resulting in the fine-
grained beds; and (3) a reelevation, which, by pushing the shores toward
the center of the field, led to the ready importation of coarse debris. It is
evident that there are many circumstances which serve to qualify the
interpretation which can be made as to this and other cycles of deposition.
Manifestly the intensity of erosion, as well as of the transportation of detritus
worn from the land, depends in large measure upon the ratio of the rainfall
at different times. As this ratio doubtless varies in different periods, or
even in different parts of the same period, the effect may be to produce
great alterations in the character of sediments brought to any particular field.
Moreover, along the coast line, when it is in a static condition, there is an
obvious tendency to produce a shelf, which, advancing from the shores of
the basin, may afford a slope over which, in time, coarse sediments may be
transported to a distance from the shore to which they could not at first
have attained. On these and other accounts it does not seem profitable
to attempt any conclusions based upon the succession of beds in this area.
ARKOSE DEPOSITS OP THE BASIK.
As the interpretation of much of the history of the Narragansett Basin
depends on the view that is taken of the arkose dej^osits which abundantly
occur at various points around its margin, and are, indeed, a characteristic
feature of that rim, it will be necessary to consider the significance of these
accumulations.
Geologists who have had to deal with arkose deposits have generally
accepted the conclusion that they indicate the accumulation of detrital
FORMATION OF ARKOSES. 51
materials derived from crystalline rocks which have been subjected to much
decay in place, so that they lost their original cohesion before they were
subjected to transportation and were accumulated in their present situations.
The essential characteristic of such deposits is that they contain considerable
quantities of crystalline materials in which the fragments have not been
reduced to sand, but retain, in good part at least, their original form. In
other words, the presence of arkose beds means an antecedent decay in
crystalline rocks, a decay taking place in such a manner as to loosen the
crystals from their attachments without going far enough to disintegrate
the bits. This action has been followed by the wearing away of the
softened mass and the more or less complete rearrangement of the
materials.
In the present state of the study of arkose beds, pains has not been
taken to discriminate the materials into the two groups into which they may
naturally be divided. In certain cases, after the process of decay has
broken up the texture of the crystalline rock, and perhaps removed much
of its materials in the state of solution, the deposit remains essentially in
its original place, where it may be covered by subsequently accumulated
deposits. Even though recementation of the crystals takes place, the
accumulation will have more or less of the character to which we gave the
name of arkose. For convenience, we may class this group as unremoved
arkose.
Although the conditions which favor the formation of unremoved
arkoses must be of infrequent occurrence, instances of the kind are to be
observed in certain parts of New England, where the preglacial decay
reduced considerable quantities of the crystalline rocks to a disintegrated
state, and where the beds thus softened were not removed by the glacial
wearing, but remain to the present day covered by sheets of stratified or
unstratified drift. The normal or transported arkoses can, in all cases, be
discriminated from those which have remained in place, by the evidences of
water action afforded by more or less obvious stratification.
The most characteristic and readily interpretable deposits of arkose
exhibited within the limits of the Narragansett Basin, indeed one of the
most important accumulations of this nature ever described, occurs at Steep
Brook, the station just north of Fall River, Massachusetts. At this point,
lying against the granitic rocks which form the western margin of the basin,
52 GEOLOGY OF THE NARRAGANSETT BASIN.
is a section of what at first sight appears to be a mass of granite which has
decayed in place. This seemed to be the view which was enforced by the
observed facts when these beds were first seen by me, about twenty -five
years ago, and they had just been opened by prospectors who were led by
a small outcrop on the brook to seek for fire clays. Further exploration,
however, soon disclosed the fact that the mass exhibited traces of stratifica-
tion such as were not to be found in the neighboring unchanged granite. A
close study of the obscure divisional plane brought to light the existence
in them of many well-preserved specimens of plants which belong to the
Carboniferous time. This evidence indicates that the deposit was formed
during the period of the Coal Measures. The considerable thickness of this
section makes it clear that the conditions which led to its formation continued
■ for a long time. These conditions were substantially as follows: There was a
rapid importation of semidecayed granitic rock, such as Avould be afforded by
the decomposition of the crystalline materials which are to be fouiad immedi-
ately to the east of the locality. The rateof this accumulation appears to have
been so speedy that there was no chance for a true soil layer to be formed
on the growing beds. The plant remains which occur were evidently not
grown on the sites they now occupy, but were fragments swept into their
positions from a distance. It appears likely that they had been to a greater
or less degree inclosed in ordinary ferruginous concretions before this
transportation.
The interpretation of the conditions at Steep Brook during the time
when the forces which led to the deposition of the arkose were in action
seems, in a general way at least, to be not at all difficult. It is evident
that in the time preceding the deposition of the portion of the Carboniferous
strata on which the arkoses lie, the portion of the continent about the Narra-
gansett Basin had been long exposed to atmospheric decay without having
been subjected to the conditions which would remove the decomposed
material as rapidly as it was brought into the disintegrated form. Judging
by the conditions which have affected the fields that now afford or that
might produce the arkose deposits, we may assume tha,t these levels of the
Coal Measures time had long been the seat of a considei'able rainfall and
had maintained a coating of vegetation, such being the antecedent condi-
tions of any decomposition which would prepare the way for arkoses.
After the development of a sufficient depth of this rock decay, we have to
DISTRIBUTION OF AEKOSES. 53
suppose that conditions favoring the rapid erosion of the decayed material
were estabhshed. These conditions may have been brought about in any
one of several ways: The region may have been subjected to glacial action;
the rainfall of the area may have been increased in such a measure that the
streams were made competent to waste the surface; or the area may have
been exposed to wave action, either by being lowered beneath the level of
the sea or by becoming- the seat of a lake.
The hypothesis of glacial action at the time these arkoses were formed
does not, at first sight, seem to be supported by the evidence which is derived
from the presence of well-preserved vegetable remains in the beds; but, as
remarked in the preceding paragraph, these remains seem not to have been
deposited in a, fresh state in the growing accumulation, but to have been
washed from some antecedently formed but practically contemporaneous
deposit into the positions which they now occupy. Therefore the existence
of ice wearing in this district at the arkose-building' time does not seem
improbable. We shall hereafter note that there is other evidence of a more
positive nature going to show the existence of glacial conditions in this
gravel period in the district a,bout the Narragansett Basin.
As a whole, the distribution of the arkose deposits of the Carboniferous
time around the margins of the Narragansett Basin seems most easily to
be explained by the supposition that streams of a swiftly flowing nature
formed torrent cones when they debouched into a fresh-water lake which
occupied almost the whole area now covered by the coal-bearing rocks of
the district. That the deposits are in general those of torrent cones or
deltas appears to be shown by their irregular distribution. In all cases
where they have been observed they occur in rather detached patches, like
accumulations which have no great extension in the direction of the ancient
shore line. This seems to exclude the supposition that the deposits were
formed in the manner of ordinary shore accumulations, where the debris
is transported from a neighboring coast escarpment.
There are no observations on record concerning arkoses now in process
of formation, thoug'h such may be accumulating in many parts of the world.
It is therefore not possible to ascertain with certainty the distance to
which the angular crystalline debris of granitic rocks can be conveyed by
stream action without losing the peculiar features which separate it from
the ordinary products of the erosive forces ^^'hich have acted on much
54 GEOLOGY OF THE XAERAGAiS'SETT BASIN.
decayed rocks. It happens that on the island of Marthas Vineyard there
are extensive deposits of arkose formed during the Tertiary period, which
appears to indicate that materials of this nature may be transported for
considerable distances. The deposits at Gay Head contain very thick beds
of arkose, probably brought from the granitic area lying to the northwest
of the locality. It is difficult to conceive that the supply of the detritus
could have been brought from less than two score miles away from the
locality in question. It is of course possible that these Tertiary arkoses
were derived from some granitic area near the place where they lie — an area
which by local subsidence or excessive erosion has in modern times been
brought below the level of the sea; but the evidence in these cases is clearly
against this hypothesis and in favor of the assumption that the little-rounded
crystals from the granitic sources have been conveyed for forty or more
miles. Therefore, while the Carboniferous arkoses afford clear evidence
that they were deposited along the shores of a basin, no very clear evidence
as to the field of their derivation can be obtained from the conditions of
the beds.
The arkose deposits of the Narragansett Basin are found in both
groups of deposits which have been observed in the field, the Cambrian
and the Carboniferous. In the former the evidence is limited to the region
about Attleboro, that being the only portion of the basin where the Cam-
brian strata are clearly recognizable. The Carboniferous arkoses are much
more extensively distributed. They may indeed be said to occur as a
characteristic feature in the margin of the basin, serving to show that, in a
general way at least, the trougli existed with something like its present
horizontal limits as early as the time of the Coal Measures. Ai no other
point are the evidences as to the conditions under which the deposits were
laid down so clear, or at least so well ascertained, as at Steep Brook, but at
all points the facts show that the matei'ials composing the beds have been
transported from a distance, and so far as determined the carriage has been
from the sides of the basin toward its central part.
It is important to note that the arkose deposits of this district appear
to have been the first of a series of erosional phenomena leading in the
end to the formation of extensive conglomerates. The stages are, first, the
arkose material, or the waste of rocks decayed in place; next, the clays and
sands, which may be regarded as the product of ordinary erosion, when
EFFECTS OF EAINFALL ON EOCK DECAY. 55
the abrasive forces keep pace with the agents of decay; and finally, the
conglomerates, formed when the abrasive actions go forward more rapidly
than those which lead to the general softening of the rocks. .
RELATION OF ARKOSES TO EROSION.
The above-mentioned facts concerning the snccession of beds in the
Narragansett Basin clearly point to the existence of what may be tei'med a
cycle of erosion dependent on the relative rate at which the two diverse
processes connected with the decay of the lands go forward. This equation,
in a general way, seems to be as follows: Where the rainfall is so slight
that a vegetal covering is not established in a countr}^, the chemical assault
on the rocks, which is due in the main to the CO2 and other products which
the decaying organic matter in the soil contributes to the ground water, is
probably wanting. The result is that the erosive work, or that which oper-
ates to remove the detritus in the form of visible sediment, though it may
be very slight, is likely to be enough to keep the rocks which have been
softened well cleared away. In such an arid country the rainfall is apt to
be irregularly distributed, so that the torrent action is at times exceedingly
strong. The result of this is that the valleys become encumbered with
angular breccia-like debris, such as now exists in the valleys of the arid
districts of the Cordilleras.
An increase in the rainfall to the point where an ample mantle of
vegetation is supplied, but short of the point where torrent action is made
excessive, tends to produce a greater amount of decayed rock than can
be cleared away. The result is that the coating of what we may term the
the nontransported arkose steadily increases in amount. The thicker this
porous layet becomes the more the rate of the torrent action approaches
uniformity, for the reason that the open structure of the decayed rock causes
the corroded zone to be an effective storehouse for the ground water, whence
it is slowly yielded to the streams. With an increase in the rate of precipi-
tation beyond the point where the water can be taken into the unoccupied
detrital layer a critical point is soon reached where the mechanical erosion
will rapidly increase and will gain on the process of interstitial decay. If
the rate of mechanical wear much exceeds that of the decay, the result will
be the deportation of solid waste in the form of pebbles, the process being
marked in a geological way by the production of conglomerates.
56 GEOLOGY OF THE NAEEAGANSETT BASIN.
We thus see that in the erosional history of a region wherein the rain-
fall varies from zero to the highest measure which we can expect, say over
1 00 inches per annum, we may look for a series of efiFects which will mark
themselves in diverse classes of debris. So long as the decay keeps in
general ahead of the abrasional work, the waste which goes forth through
the streams is likely to be of a finely divided nature, giving rise to clayey
slates as the natural product. If a stream yields abundant materials which
would form arkose, it is because the erosion is gaiiaing on the decay. If
the work produces pebbles, the indication is that the jnechanical erosion is
so great that wearing by solution plaj's no important part in the process.
In this connection it Avill be well to note yet further that the large
production of pebbles within a short time can scarcely be accounted for
except on tlie supposition that the abrasion has been brought about by the
action of glacial ice. As the importance of this proposition has not been
appreciated by those who have dealt with the problems afforded by con-
glomerate deposits, we must note that there are but three ways in which
waterworn pebbles can be made in sufficient quantities to afford materials for
ordinary conglomerates. The first and practically the only effective means
by which pebbles can be extensively made — i. e., in large amount per unit
of surface over a large area — is by glacial action. Where the precipitation
of a country goes off as an ice sheet, every portion of the rocks over which
it flows, if the material be sufficiently hard, becomes a part of a vast
bowlder factory — for such, in fact, is all the-base on which the glacier rests.
As the average thickness of the till covering in the glaciated district of this
country is not less than 10 feet, and as the greater part of this till is bowl-
ders, it is clear that ice in motion is specially adapted to forming such partly
rounded bits of stone. The materials in our eskers show how successful
the subglacial torrents, with their currents impelled by hydrostatic pressure,
were in completing the rounding of pebbles which the ice began to shape.
When the rainfall of a country goes to the sea in a fluid state, the tor-
rent section of its river system, provided the rate of decay is swift, is likely
to be the seat of the production of a considerable amount of pebbly mate-
rial. Yet the share of the energy of the portion of the rain water which
is then effectively applied to joebble making is but a small fraction of what
is used when the same amount of precipitation g'oes to the sea in the form
of a glacier. Moreover, the pebbles which are thus formed in ordinary tor-
CONDITIONS OP PEBBLE MAKING. 57
rents are made in small quantities. No sooner does a torrent bed become
loaded with this detritus than it ceases to be an effective factory of the
rounded bits of stone. Furthermore, the pebbles which are formed in tor-
rent beds rarely attain the sea or any position where they can be built into
extended beds of conglomerate. Although I have inspected several thou-
sand miles of seashore, much of it along mountainous coasts, I have never
found a place where pebbles, such as are found in the conglomerates of
the Narragansett Basin, from a stream of any size were entering the sea.
It may, indeed, be regarded as rare for a stream to discharge into the ocean
pebbles exceeding an inch in diameter. To do such work it would have to
flow at a torrential rate at its very mouth, a condition which can be found
in certain fresh-water lakes, but is rarely seen on the ocean coast line.
The third means of pebble making may be seen along the seashore
where the waves are attacking hard rock cliffs. In such conditions pebbles
are formed, but they are rarely accumulated in large quantities ; in general
the fate of coast-made pebbles is to be worn out by the action of the forces
which have shaped them. There are no agents whereby siich marine
pebbles in considerable quantities can be carried out for any distance from
the shore. In rare cases ice forming- along the coast is likely to inclose
some portion of the shore debris; this shore ice may then drift out to sea
and there deposit the load of pebbles which it has rafted. This action,
though sufficient to strew the sea floor with shore-made stones, can not be
looked to as a means of accumulating conglomerates.
The above-mentioned considerations make it clear that it is not easy
to account for the existence of widespread deposits of pebbles of consid-
erable size accumulated in massive strata, which in the case of the beds of
the Narragansett field contain perhaps more pebbles than exist on the beaches
of the Atlantic coast or in all the torrent beds of the Appalachian Moun-
tains. The easiest way, if not indeed the only way, to explain the forma-
tion of extensive conglomerates is as follows: On the surface of a land area
there must first be accumulated a considerable deposit of rock fragments,
such as is normally gathered at the close of a glacial period, or such as
occupies a region of high relief, scanty rainfall, and much frost work, after
the manner of large areas in the Cordilleras and in other parts of the world
where these conditions exist. If, now, such a fragment-strewn district is
gradually lowered through the mill of a shore line either of the sea or of a.
58 GEOLOGY OF THE NAERAGANSETT BASIN.
considerable lake, the chance for the formation of normal conglomerates
will be provided. The unorganized debris of the surface will be taken to
pieces and recomposed into stratified beds, as is now being done with the
glacial debris along the shores about the North Atlantic. In this formative
process the pebbles are likely to be changed in shape and assorted as to
size in a way which at once distinguishes the strata into which they are
built from the beds of till or of residual breccia from which the fragments
were derived.
There are certain tests of some value in distinguishing the conglom-
erates made from rearranged glacial materials from those which owe their
formation altogether to marine action. Pebbles made from fragments
which have long been separated from the bed rock are generally, unless
they be of quartz, much affected by decay; they contrast distinctly with
the fresh quality of the ordinary glaciated pebbles. As I have observed
in the southern part of this country, as well as in southern Europe, the
detrital waste which comes into the streams is generally so penetrated by
decay that it can not be made into pebbles ; if perchance it holds together
in the shaping, the eye at once separates the bit from those which are made
from freshly riven stone.
Where pebbles are made by wave action alone, it is a notable fact that
they exhibit very little diversity in form; they are almost invariably sphe-
roidal, and when they are accumulated in considerable numbers the litho-
logical diversity of the material is small. Although glaciated pebbles are
apt to be somewhat altered from their original subangular shapes as they
pass through a surf line, many of them, as we may note along the New
England coasts, will withstand a deal of hammering without losing the dis-
tinct mark which the ice work impressed upon them. Moreover, taken col-
lectively, whether in the original till or in the partly masked shore deposits,
they commonly exhibit a large petrographical range of material. The facts
which are available for the interpretation of conglomerates show that those
of the Narragansett Basin are of what we may term secondary glacial
origin. This is indicated by their frequent — Indeed, we may say usual — sub-
angular form, their petrographical variety, and the very small amount of
decay which had affected the rock masses after they left their original bed-
ding places and before they were deposited in the situations in which we
now find them.
EVIDENCE FROM CONGLOMERATES. 59
The hypothesis that the coiaglomerates of the Cambrian and Carbon-
iferous as exhibited in this locaHty are the -results of glacial action is sup-
ported by the general distribution of such deposits in this and other
countries. Massive conglomerates of great areal extent are distinctly more
common in high than in low latitudes. With rare, and in most cases
questionable, exceptions the deposits of this nature which can be traced
horizontally for a great distance from north to south fade away as they
approach the equator. As our study of conglomerates advances, more of
the deposits are found to aiford evidence as to the glacial origin of their
pebbles. The great conglomerates at the base of the Carboniferous in
India, which from their interstratified position appeared not to be open to
the explanation which has been advanced in this writing, have recently
afforded clear evidence to show that glaciation, possibly occurring at a
time when the area was elevated to a great height above the sea, suffi-
ciently accounts for the origin of the pebbles and bowlders which the beds
contain.
Although this is not the place for an extended discussion of the matter,
it may be worth while to remai-k that a collation of the recent studies on
conglomerated deposits clearly shows that we are fast approaching the
point where beds of this nature will be taken as presumptive evidence of
glacial action occurring at the time, of their deposition, or perhaps imme-
diately jJi'eceding it.
RECORD VALUE OF COISTGIjOMERATES.
In connection with these considerations relating- to conglomerates, it
may be well to note that deposits of this nature have another much neg-
lected element of value to the geologist, in that they afford him an opportu-
nity to ascertain many facts concerning the physical conditions of the region
in which they occur at the time of their formation. Although the value of
these indications is in good part self-evident, they have been so generally
neglected that it is worth while to dwell upon the methods of using them
and to illustrate them by a special study of the Narragansett field.
If a conglomerate has not been subjected to metamorphic action
sufficient to change the original character of its jaebbles, these fragments
may be taken as evidence concerning the state of the rocks whence they
came at the time the j)ebbles were brought together. This evidence.
(50 GEOLOGY OF THE NAREAGANSETT BASIN.
when examined, is seen to go very far, and in several directions. In the
first place, the conglomerate may be taken as representing the beds which
were exposed to erosion at the time it was formed. If the beds are of
ancient and of known age, they may enable us to determine the former
existence, in the field, of rocks which have since disappeared by erosion,
been lowered beneath the sea level, or been covered over by other deposits.
Thus, in the case of the Carboniferous conglomerates of the field under
consideration, we find in the beds a very great immber of quartzitic pebbles
which contain fossils evidently of the Cambrian age. It is clear that the
field occupied by the quartzites was extensive, for the fragments which
appear to be of that group of rocks, though not always containing fossils, are
about the most numerous of the components which make up some of the
thickest layers of the Carboniferous conglomerates. A carefiil search of the
rocks of eastern Massachusetts has failed to reveal the source of these fossil-
bearing pebbles. Strata perhaps about the same age are found in various
parts of eastern Massachusetts, but they are lithologically and in fossil con-
tents very different from the strata which afforded the pebbles. While it is
possible that the field whence the quartzite bits came has, by differential
warping, been carried beneath the sea, it is rather improbable that such has
been the case; it is more likely that the rocks in question lay on the margin
of the basin, whence by erosion they have disappeared.
It is a noteworthy fact that the above-mentioned quartzite is the only
rock of the many contained in the Carboniferous conglomerates which has
disappeared from this part of the country since these beds were formed.
There are, it is true, certain uncharacteristic sandstone pebbles which
can not clearly be identified with anything now in or about the basin, but
these are not numerous. The impression left by the stud}' of the Coal
Measures pebbles is that the general character of the rocks exposed at the
surface in this field in Carboniferous time was substantially the same as
that of the rocks remaining at the present time. This view is justified by a
comparison of the materials contained in the ancient and the modern aggre-
gations of glacial waste. Taking pains to exclude from the waste of the
last Glacial period the pebbles which have been worn from the basin rocks
of this field, the observer is at once struck with the likeness of the two
assemblages, a likeness which shows us that the erosive agents found, with
the exception of the above-noted quartzites, much the same rocks open to
TIME OF METAMOEPHISM. 61
their assaults in these two periods, which must have been separated by
some miUions of years.
The fiekl open to examination is much more Hmited in the case of the
Cambrian conglomerates than in that of the Carboniferous pudding stones.
Moreover, the pebbles contained in the beds have been subjected to more
metamorphism. Nevertheless, the studies which have been made show that
the rocks of the fundamental complex had attained about their present con-
stitution before the beginning of the Olenellus epoch. These pebbles rep-
resent the granites, gneisses, quartzites, etc., of the rocks which are found
beneath the Cambrian beds, and show that the crystalline condition of these
deposits was approximately the same as it is now. It is evident, however,
that there were quartzites and other semimetamorphosed beds which afforded
waste to erosion in the Olenellus epoch, beds which are not recognizable as
in place in the district, and which perhaps, like those noted in connection
with the Carboniferous, have disappeai-ed from the district. It is neverthe-
less clear that the greater part of the crystalline rocks of this district were
already not only in their present mineralogical condition, acquired during a
period when they had been deeply buried beneath other rocks, but had been
stripped by the erosive forces of this ancient covering.
It must not be supposed that the whole or even the greater part of
the metamorphism which has taken place in this region had been accom-
plished by Cambrian or even Carboniferous time. While in certain districts
and with certain rocks this work seems to have been then completed, or
nearly so, in other parts of the field the action continued at least until after
the deposition of the Coal Measures strata. Thus the beds of the last-
named series in the region about Worcester and in that about Wickford
have been transformed to gneisses which, but for collateral evidence, could
not be recognized as having been, in their original state, the associates of
ordinary coals. It is evident that in this last-named field the process of
metamorphism has gone on with exceeding irregularity, certain parts of the
most ancient deposits — as, for instance, the fossiliferous strata of the Olenellus
horizon — being not much altered beyond the induration common to all
ancient flaggy layers, while bat a few miles away cong-lomerates have been
so far converted into crystalline rocks that the original character of the beds
has been almost completely lost.
Q2 GEOLOGY OF THE NAERAGANSETT BASIN.
RED COiOR OF THE CAMBRIAN AND THE CARBONIFEROUS.
The red hue of certam portions of the Cambrian as well as of the
Carboniferous rocks affords a matter for inquiry. Though no solution of
the problem has been attained, it may be well to note certain facts of possi-
ble value to those who may hereafter attack the question. It is noteworthy
that the red beds of both the above-mentioned series occur on the western
and northern sides of the Narragansett Basin and in the trough of the
Norfolk Basin. In both these sections the red beds are somewhat irregu-
larly distributed, generally occurring between deposits which have no trace
of the peculiar hue. In some cases, as noted by Mr. Woodworth, the red
stratum may be but a few inches thick, lying between sandstones or arkoses
of a whitish hue. This peculiarity of distribution is also very noticeable
in deposits exhibited at Gay Head and elsewhere on Marthas Vineyard
which, in Cretaceous and Tertiary time, were made under conditions some-
what similar to those which existed in the earlier periods when the Narra-
gansett deposits were formed.
It seems likely that the red hue of stratified deposits is due to a variet}"
of actions. In some instances, as along the present coast Ihie of the region
and about the mouth of the St. Lawrence, red beds may be formed by the
disintegration of Triassic or other red sandstones and clays, the rearranged
material retaining in large measure the hue of the rocks Avhence the d(ibris
came. In other instances, perhaps in the case of the Cambrian and possi-
bly the Carboniferous of the Narragansett field, the red hue may be due to
the fact that the beds thus colored originally contained a share of lime car-
bonate. Downward-percolating waters containing iron oxide transformed
these beds first into impure siderite, and further change served to bring the
iron into the state of limonite. The coloration thus brought about is fre-
quently to be observed in the Devonian and Silurian rocks of the Appala-
chian district, being particularly conspicuous in the iron-bearing members
of the lower Devonian and ujjper Silurian strata of eastern Kentucky, as
for instance in Bath County. In yet other instances the decay of crystal-
line rocks containing a considerable share of iron may have provided the
ferruginous mateiial in a direct manner in the process of sedimentation.
Some unpublished studies as to the amount of magnetic oxide in the drift
covering which exists in this part of New England have shown me that the
EED COLOE OF CAMBRIAN AKD CARBONIFEROUS. 63
propoi'tion of this material ranges from about one-half of one per cent to
as much as five per cent by weight of the mass. As further oxidation of
these crystals of magnetic iron goes on but slowly, the deposits in which
they finally come to rest may contain a large share of the material which is
to be, by fuii;her change, dissolved and distributed through the bed. Even
where the ferruginous matter has been accumulated between the fragments
of rock in the form of a thin vein or coating separating the bits, it may by
a further process of change lose the iron in a greater or less measure and
become a mere stain.
CHAPTER III.
GLACIAL HISTORY OF THE NARRAGANSETT BASIN.
The interpretable history of this basin, so far as it has depended on the
action of ordinary streams and of the sea, has ah-eady been set forth. This
account of the effects of the solar energy which has been appHed through
the atmosphere needs to be supplemented by some consideration of the
work which was done during the Glacial periods. The account which will
here be given of the work will in the main be restricted to the phenomena
that are in some measure peculiar to the field, for the reason that the surface
geology of New England is to be the subject of a separate publication by
the Geological Survey. Any full discussion of these matters in this memou-
woidd therefore involve ah undesirable repetition.
We may first note that the deposits formed during the times repre-
sented by the conglomerates of the Carboniferotis series have a character
which warrants the hypothesis that they are to a considerable extent the
products of glacial action. The view that this age was a period of recurrent
ice work has already been ably presented by the late Dr. James CroU.
Here, as elsewhere along the Appalachian district, the supposition is sup-
ported by an array of facts which deserve more attention than they have
received. These facts, as they are exhibited in the country from Alabama
to the St. Lawrence, will be briefly set forth.
CARBONIFEROUS COXGIiOMERATES.
In the Southern States the conglomerates of the Carboniferous periods
are, with rare and unimportant exceptions, made up of pebbles of quartz,
which, as has been noted by several observers, are evidently the remains
of the uudecayed veinstones that survived the decay which, in the pre-
Carboniferous, as in the modem time, greatly aff"ected the rocks that were
exposed to the atmospheric agents. The great thickness of these quartz
(JAHBOMFKRUUS CONGLOMEHATivS. ' (55
couglomerates, their wide distribution, as well as the general absence of
fossil remains, are best explained on the supposition that the erosion
took place in an ice time, being effected by the glaciers or by the currents
of living water which coursed beneath them. In no way save by com-
paring this ancient work with that now in progress in glaciated regions can
we well account for the deposition of the Millstone grit of the Southern
Appalachians.
As we go northward from the valley of the Tennessee the Carbonifer-
ous strata show an increasing amount of pebbly material which has been
derived from the undecayed bed rocks. As elsewhere noted, these rocks
indicate that there was at the beginning of the period a considerable thick-
ness of decayed material, but before long the erosive agents had removed
this friable mass, and thereafter the supply of pebbly matter, vast in amount,
was obtained by the breaking up of bed rocks which show no evidence
that they had been affected by superficial decay. As we go yet farther
north, in the next field where the rocks of this age appear, i. e., in the region
about the south shore of the St. Lawrence, the thickness of the conglomer-
ate even exceeds that of the sections hereafter to be described in the north-
ern part of the Narragansett Basin. In a word, the facts make it evident
that the Carboniferous period of the eastern part of North America, like
certain other periods, was one of exceedingly rapid alternations between the
conditions which favored the development of marsh vegetation and others
under which the accumulations of coarse sedimentary deposits went on with
great rapidity.
Although there are instances in which a torrent may accumulate a
large detrital cone composed of bowlders and pebbles, I know of no geo-
logical machinery now at work on the earth's surface, or which can reason-
ably be supposed to have operated in the past, except glaciation, that is
competent to produce such immense masses of coarse detritus as are contained
in these conglomerates, or bring them into position where water action can
effect their arrangement into beds. The area of the deposits lying on the
two sides of the old Appalachian axis probably now exceeds 60,000 square
miles; the average thickness of the section is certainly not less than 2,500
feet; so that the amount of matter of a prevailingly coarse nature which
was laid down along the old Appalachian ridge in a period apparently of
no great duration was not less than 20,000 cubic miles, and probably was
MON xxxiii 5
QQ GEOLOGY OF THE NARRAGANSETT BASIX.
far more than that amount. When we remember that the whole drainag'e
basin of the Mississippi — a region which is probably many times as great
as the field whence this detritus came — yields to erosion not more than
about a twentieth of a cubic mile each year, it becomes evident that we
have to bring into our conception of the causes operating in the olden day
some more effective agent of erosion than is found in free water.
If all the detritus of the Carboniferous conglomerates were of the same
nature as that which is found in the Southern Millstone grit and the related
beds, we could perhaps assume that their production was due to the invasion
of the sea acting upon a deep decayed zone, but the fact that the thickest of
these deposits occur in the northern part of the Appalachian field and are
composed of undecayed pebbles negatives this hypothesis and requires
us to assume that the erosion attacked the bed rock with great intensity.
That this attack was by torrent action is extremely improbable; for, as
before stated, no torrents are now known to produce so large amounts of
pebbles of crystalline rocks as were formed at this time; and when such
fragments are formed, so far as my observations go, they always present
marks of decay, due to the slow manner in which they are shaped and to
the conditions of their storage in detrital cones. The pebbles of the
Narragansett and other conglomerates of the same age which I have
examined, even those of a compound nature, are in practically all cases as
fresh as those contained in the bowlder deposits which were formed during
the last Glacial period. This appears to negative the supposition that they
could have been the result of ordinary torrent action and to require a
method of formation which apparently can be explained on the hypothesis
of glacial erosion.
It should be noted that the pebbles of the Carboniferous conglomerates,
especially in the Narragansett district, show no trace of glacial scratches;
moreover, they generally have a rather rounded form and are of less varied
size than those in any of the till deposits formed during the last Glacial
period. In some cases, however, they seem to me to retain the faceted
shape which is so characteristic of ice-made pebbles. When compared with
the pebbles of the last Glacial period, which, in a measure, have been sub-
jected to marine or stream action, they are found to coiTcspond with them
in all essential features, except when, as is often the case, the old fragments
have been deformed by stresses which came upon them since they were
GLACIAL PHENOMENA. 67
built into the Carboniferous strata. The absence of large bowlders in the
Carboniferous is paralleled by what we find in the modern washed drift;
there, as might be expected, the larger fragments have been kept out of the
beds by the sorting process which takes place in water transportation.
The facts disclosed by a study of the conglomerates of this basin lead
to the conclusion that the pebbles were probably formed by glacial action,
and that the fragments were brought to their pi-esent position by torrents
which swept into the basin from the highlands that bordered it. Their
transportation to their present sites, as well as their distribution into beds,
may have been due to waves and shallow-water currents acting during a
period of increasing depression of the land. In no way save by glacial
work does it seem to me possible to account for the rapid formation
of the great mass of pebbly detritus which is contained in these beds. It
therefore may fairly be held that the Carboniferous period, in this district
at least, was one of extensive and long-continued glacial action, and that
the greater part of the section exhibited in the basin is made up of rocks
which owe their more important features to the action of glaciation. From
the Carboniferous to the Pleistocene this area affords no evidence of ice
action.
liAST GliACIAI. PERIOD.
The last Glacial period has left upon this district marks of its action
which are as indubitable as any that are found in the region to the north-
ward. In the time of the greatest southward extension the front of the ice
evidently lay considerably to the south of the whole southern shore of Mas-
sachusetts, Rhode Island, and Connecticut. This is shown by the presence
of extensive moraines on the Elizabeth Islands, Marthas Vineyard, and Nan-
tucket, as well as on Long Island, New York. A careful inspection of the
marine soundings off this shore has failed to reveal any indications of a
submerged moraine marking the extreme line to which the ice sheet
attained. Moreover, the evidence gained by the study of the front over
the land from the coast of New Jersey to the far West goes to show that
the extreme extension of the ice was of a very temporary character, the
considerable halts having taken place in the stages of retreat which probably
began very shortly after the farthest southward advance had taken place.
The stages of retreat of the glacier in and near the Narragansett Basin
are fairly well marked by the occurrence of frontal moraines. These
gg GEOLOGY OF THE NARRAGANSETT BASIN.
moraines consist in part of ridges composed of glacial waste, in charac-
teristic, irregular, shoved attitudes, each ridge with a more or less distinct
sand plain or frontal apron on the side which lay away from the ice, and
in part of bowldery tracts where the glacier did not build a distinct or
frontal wall or where it may have overridden or broken down the barrier
after its construction. It should be noted that these moraines, unlike
those on Long Island and Marthas Vineyard, are not placed at right
angles to the general trend of the ice movement, but on the west side
of Narragansett Bay are turned into a nearly north-and-south position.
Beyond the head of the bay they again turn more nearly to the east-
and-west direction. On the eastern side of the basin the ridges are not
traceable with sufficient distinctness for mapping, but the outlines of the
ice front at the time of the formation of this moraine are well enough
shown to make it plain that there was a deep indentation at that point, so
that while the ice overlapped the present shore on either side of the basin
the front did not extend much south of Taunton. Such lobations of the
margin, as they have been termed by Chamberlin, were very common
along the front of the great ice field. They are due to irregularities of
the surface over which the ice moved or to other local conditions. In other
instances the presence of a deep, broad valley, such as is afforded by the
channels of the Narragansett Bay, led to the projection of the ice at its
mouth beyond the main line of the front. In this instance the retreat of
the front was probably due to great volume of the subglacial streams which
flowed from the areas to the northward. Their effect on the ice at the
margin would be to melt it away at the base, making the formation of ice-
bergs an easy matter. As the region was evidently depressed below its
present level at the time the ice was most advanced — lowered, it may be, to
some hundi'eds of feet below its present altitude — the undermining- action
of the waters would naturally tend to detach bergs.
It is evident that the ice front in the region between the northern part
of the basin and the sea was subjected to many alternations of advance and
retreat which are not registered in any distinct moraines. About twenty
years ago, when the Old Colonj^ Railroad Company was widening its road-
bed, the new-made sections distinctly showed that there had been a score
of these oscillations in the line from North Easton to Somerset, each marked
by the disruption and erosion of the deposits which had previously been
GLACIAL DEPOSITS. (>9
formed at the front of the ice. The same evidence is visible at the present
time, though less distinctly, in similar cuttings which are making from
Brockton southward. The result of these irregular movements of the ice
has been to give the drift deposits of this field a peculiarly irregular and
confused character. The greater part of the eskers or ridg'es of sand, gravel,
and bowlders which were formed within the ice-carved channels that were
excavated by the subglacial streams has been effaced.
It is a notable fact that in the southern part of the basin, on the shores
and islands of that part of it which is included in Rhode Island, eskers are
essentially absent, except near the moraine which borders the western
margin of the field. This seems to be due, not to the successive advances
and recessions of the ice front, but rather to the fact that the very deep chan-
nels of the bay provided ample low levels through which the subglacial
streams made their way to the sea. In the district between the railway
bridge at Somerset and Steep Brook Station there is an extensive and very
characteristic area of those "pitted plains" which are often found near where
a sifbglacial stream discharged its cu^rrent into open water. The area
which now remains is evidently only a fragment of the original field. The
materials seem to have been brought to their position by an under-ice
river which followed in general the line of the present Taunton River. The
cause of the pittings is not yet determined, but they are probably due to
the embedding of masses of ice in the swiftly accumulating detritus, these
small bergs being weighted down to the bottom by the amount of rocky
matter which they contained; when they melted, the originally level
surface fell into its present shape.
The till or bowlder-clay coating of this district is, on the average, less
thick than in the region lying immediately to the northward; wherever the
section extends to the bed rock this most general element of the drift — the
waste dropped on the rocks in the last retreat of the ice — is commonly found
to have a thickness of less than 10 feet. Although this till sheet, when it
covers rounded masses of the bed rocks, often takes on a drumlin aspect, it
seems clear that there are none of these peculiar lenticular hills in the basin.
Their absence on the margin of this part of the continental glacier is in
accord with their distribution in other parts of this country; they are
evidently due to the conditions which prevailed in the portion of the ice
which lay near the margin, but not usually within 50 miles or so of its verge.
70 GEOLOGY OF THE NAliRAGANSETT BASIN.
It is to be noted that the till materials of this basin contain a much
smaller amount of clay than is the case with the like deposits farther inland.
This is probably due to the fact that in this marginal district the materials
composing the till consist largely of esker and other washed gravels that
had already lost their clay element. In the irregular movements of the ice
and of the subglacial streams a large part of this clayless matter is brought
again into the ice, and in the end finds its way to the surface in the form of
till. The result is that in this marginal portion of the glacial field in New
England there is often little difference in the materials which go to make
up till or kame deposits, the clay element having been in both cases washed
away. The effect of this is to make the value of the fields for tillage
much less uniform than is the case where the till deserves its ancient name
of bowlder clay.
The origin of the glacial detritus of the Narragansett Basin has not
yet been fully traced. From the studies which have been made it is suffi-
ciently evident that the carriage in the case of the materials contained in the
till has in general been for no great distance. Although, as will hereafter be
noted, there is at least one case where the transportation has extended very
far, the evidence shows that at least four-fifths of the till ddbris has been
carried not more than 5 or 6 miles. This determination is easily made on
the northern border of the basin, where the line between the pre-Cambrian
and igneous and the Carboniferous rocks can be traced with approximate
accuracy. The materials which have been conveyed in the subglacial
streams, here as elsewhere, have been subjected to much greater transpor-
tation. The exact extent of this has not been determined, but it has
probably amounted to many times the distance of the carriage of the
materials which form the till.
A large part of the waste which enters into the composition of the drift
of this district has come from the disintegration of the conglomerates of
the Carboniferous section. This is shown by the fact that a considerable
portion of the drift pebbles retain the distinct form which was given to them
by the stresses to which they were subjected in the beds in which they had
lain so long, and also by the fact that these pebbles are often composed of
the fossiliferous quartzite which yielded so much to the debris in the Car-
boniferous time, but does not now exist in the original bedded form in any
part of the district. The fact that the glacial deposit in the older moraines
GLACIAL EROSION. 71
contains relatively few large bowlders which have been derived from the
conglomerate, while the pebbles from that source are extremely abundant,
is worthy of note. Thus, on Marthas Vineyard, where the bowlders and
pebbles which lie on the Cretaceous and Tertiary rocks have all been
imported from the Narragansett Basin, the amount of pebbles which have
been separated from the matrix of conglomerate is very great, but the
number of bowlders of the conglomerate rock is so limited that an inspec-
tion of a thousand of these erratics revealed only half a dozen of this
nature, the others being from the granitic and other old rocks which form the
margins of the basin or from some of its inliers of like rocks. In its ordi-
nary undecayed state the conglomerate fractures in such a manner that
the rift intersects the embedded pebbles. We are therefore justified in
believing that at the +ime the glacial flow began to attack this region the
deposits were decayed to a considerable depth, so that the attrition broke
up the adhesions and separated the pebbles from the matrix. The fact that
the bowlders of the massive conglomerate are very rare in the inoraine of
Marthas Vineyard, which was formed at an early stage of the ice time,
while they are relatively much more common in the drift lying in the basin,
gives stxpport to this view. It is certain that the debris from this basin
which is found in Marthas Vineyard was derived from the area in the
earlier stages of the glacial excavation, while that formed on the surface of
the conglomerate represents, of course, the last part of the erosion which
was effected.
AMOUNT OF EROSION.
Although the amount of erosion which was accomplished by the ice
in the last Glacial epoch can not well be determined, the evidence goes to
show that it was considerable. Thus the moraines in Falmouth and on the
island of Marthas Vineyard and the Elizabethan group, all of which appear
to owe their materials in the main to the rocks of the basin and its margins,
contain in the aggregate a mass of matter which, evenly distributed over the
basin, would cover it to the depth of several feet. It is not to be believed
that these accumulations represent anything like half the rocky matter
which was worn away from the Narragansett district. Better evidence
as to the amount of erosion, as well as much information concerning the
distance to which the drift has been carried, is afi"orded by the bowlder
trains of this field. These trains are traceable from certain of the peculiar
72 GEOLOGY OF THE NAEKAGANSETT IJASIN.
deposits of the district to distances which vary with the endurance of the
particular kinds of rock. The crystalhne hmestones of Lincohi form trains
having a traceable length of from 4 to 5 miles; after a journey of that
length the rather soft bowlders seem to be quite worn out. The exceed-
ingly hard ilmenitic magnetite which occurs in Cumberland near Woon-
socket, Rhode Island, has yielded the most perfect bowlder train that has
3'^et been traced in this section of the country. Originating in a deposit
which has a Avidth transverse to the path of the ice of only a few hundred
feet, this train extends in a gradually broadening path to the outer or
southern part of Narragansett Bay in a nearly north-and-south course;
thence it appears to have been deflected easterly, so that it overlapped
the western peninsula of Marthas Vine5^ard, known as Gay Head. In that
district foiu- or five specimens of the unmistakable rock have been found,
which afford sufficient evidence that the train extended at least 60 miles
from the point of origin.
In a description of the Iron Hill bowlder train,^ I have given a detailed
account of its phenomena; and an estimate, based on such data as were
obtainable that served to show the amount of the rock in the deposit, was
that the amount of erosion which had taken place at Cumberland Hill
during the Glacial epoch was not less than 60 feet. In reviewing the facts,
it seems to be evident that this estimate is undei' rather than over the truth.
It is not unlikely that if all the waste from this elevation which was
removed by ice action could be restored, the summit would be near 200
feet above the present level. It is not to be supposed that the amount of
erosion in the Narragansett area was as great as that which occurred at
Iron Hill. At the time the ice began to act, that mass was probably at a
much higher level in relation to the suiTounding counti-y than it is at pres-
ent; it is likely that the processes of decay had penetrated deeply along the
numerous joints, so that when assailed by the ice it rapidly broke up.
However, making what seems to be all due allowance for this probably
greater erosion in this point, it must be confessed that, taken with the evi-
dence before adduced, it serves to show that a considerable thickness of
beds, perhaps near 100 feet of rock, must have been worn from this area
during the time the ice lay upon it.
'The conditions of erosion beneatli deep glaciers, Tjased upon a study of the bowlder train from
Iron Hill, Cumberland, Rhode Island, by N. S. Shaler: Bull. Mub. Comp. Zool. Harvard Coll., Vol.
XVI, No. 11, .January, 1893, pp. 185-225, 4 pis. and map.
OHANNELS OF BAYS. 73
It is well to contrast tlie rapid and effective erosion work of the conti-
nental glacier with the relatively very slight action that free water or
atmospheric decay has had upon the rocks of this district since the ice
mantle passed from its surface. Since the surface entered on its present
state there has been but very little decay of the rocks. Even where they
have remained without a covering of soil, as is the case in the summit of
Iron Hill, the penetration of decay in most instances is inconsiderable, and
the actual loss of material is so slight that the lowering of the surface has
not on the average exceeded 2 or 3 inches. In some cases bosses of the
harder conglomerate which have had no other protection than a coating of
lichens and the thin layer of detritus which they gather on a steep slope,
still retain the deeper groovings which the ice impressed on them. So far
as the bed rocks are concerned, the removal of matter from this region since
the close of the last Glacial period has been entirely unimportant, and the
decay, such as has penetrated so deeply in the Southern States, has hardly
begun even in the most advantageous situations for the process. These
facts point to the conclusion that the period which has elapsed since the ice
left this district has been, in a geologic sense, very brief
It is to be noted that the channels in which the main arms of Narra-
gansett Bay lie are still rather deep, though their bottoms are probably
covered by a considerable thickness of drift materials, both that which was
originally deposited when the ice was retreating and that which has been
swept to its place by tidal action. The question suggests itself as to what
extent these depressions are due to the direct cutting action of the ice and
what to the concomitant action of the subglacial streams. While it must be
admitted that the general distribution of the channels of the bay and their
relation to the river channels connected therewith favor the supposition
that the arrangement of the valleys is in the main the result of ordinary
river action, it can not well be denied that the glacial work greatly changed
the forms and in a measure the distributions of these depressions. Thus
the several rocky islands of the bay, with deep water between them, can
not well be explained by the supposition that they are the remains of
divides which once separated adjacent parallel river valleys. The channel
between Bristol Neck and the north end of 'Aquidneck Island appears to
be inexplicable on the theory of a submergence of river topography, but
it may be accounted for on the assumption that it is due to glacial scouring.
74 GEOLOGY OF THE NARRAGANSETT BASIN.
It is to be noted that the general form of the basin is such that the ice
during the period when its front lay beyond the present shore line of the
continent, as it probably did for the greater part of the time in which it
occupied this part of the country, was led somewhat to concentrate its
flow in the relatively narrow space occupied by the seaward part of the
basin. This concentration must have increased the speed of the move-
ment and thereby the erosive effect of the moving ice. I have elsewhere^
endeavored to show, by clearer examples than are afforded by this field,
that the effect of such an increase of speed, due to the crowding of ice into
a relatively naiTOw way, is to intensify the erosive work which the ice per-
forms. It is also clear that the subglacial streams which discharged into this
bay were very large. Such streams, so long as they flow beneath the ice,
probably have a far greater cutting power than open-air rivers, for the rea-
son that they move with an energy in some measure intensified by the
height of the column of ice whence they are derived. As the sheet may
well have had a depth of some thousand feet, the impulse can be accounted
as great. These subglacial streams were competent to urge forward over
level ground the bowlders, often several feet in diameter, which we now
find embedded in the eskers — masses which the most vigorous mountain
torrent would hardly be able to move. We may therefore reckon the sub-
glacial streams as powerful agents of erosion, quite competent to deepen
channels such as the preglacial rivers may have formed or to cut new ways
if the conditions compelled them to flow in other courses.
It must be said that the form of Narragansett Bay is not that of a
characteristic fiord, such as in the regions farther to the northward clearly
attest the competency of glacial ice to excavate such basins. There is no
trace of the sill or rock barrier across the mouth of the bay, separating it
from the sea, such as marks the normal Scandinavian fiords. We may,
however, hold that while this Narragansett system of depressions is clearly,
as regards its general outlines, the product of erosion work done before the
ice time, it owes much of its form to glacial processes.
Before closing this brief account of the glacial phenomena of the Nar-
ragansett district which demand notice in this memoir, we may refer to the
general form of the surface of the basin with reference to the jjossible effect
' The geology of the island of Mount Desert, Maine, by N. S. Shaler: Eighth Ann. Rept. U. S. Geol.
Survey, Part II, 1889, pp. 1007, et seq.
DECAY PREOEDIFG GLACIATION. 75
of ice action in shaping the area. The facts presented in this report clearly
indicate that the bed rocks have been cast into exceedingly varied flexnres
and faultings. As these disturbances involved a great thickness of strata
and were made apparently in a geologically short period, the result must
have been the formation of mountains of high relief Yet these elevations
have been so completely effaced that, as is shown in the maps, the region
is now in the state of a great plain, the trifling differences of elevation
being due to the action of the rivers and the subglacial streams. As before
remarked, the modern school of geographers Avould attribute this topographic
character to the process of base-leveling, by which, through the atmospheric
agents of erosion, a surface, however diversified, tends inevitably to be low-
ered to near the level of the sea. Making what seems to be due allow-
ance for the effect of repeated elevation in refreshing the work of the
streams and thus promoting the degradation of a countfy, a cause which
most likely operated in the West Appalachians more effectively than on this
seashore, there still seem to be needed some agents to explain the remark-
able planation of the district we are considering. It is likely that glaciation
has been one of those auxiliary agents. We will now consider the way in
which it may have operated to bring planation about.
The evidence has been noted which goes to show that the rocks of this
basin were deeply decayed at the time the work of the last Glacial period
began. Acting on such a surface, the ice would quickly become burdened
with an excess of ddbris,in which state it would resemble an ordinary stream
of water which has a charge of sediments much greater than it can carry.
In this case both the fluid and the viscous streams necessarily tend to
deposit a part of their burden and to flow over the accumulations, being
thus in part excluded from contact with the bed rock. The deposits of the
overburden would naturally take place in the valleys, the floors of which,
except when attacked by the subglacial streams, would remain uneroded,
while the higher-lying parts of the field would be cut away. As the process
of erosion advanced and the waste from the elevated places became smaller
in quantity, the glacier would be free to attack the lower levels. The result
of this succession of events would be to level off the inequalities of a country
which, owing to the decayed state of the rocks at the time the ice came
upon it, afi"orded detritus more rapidly than the machinery of transporta-
tion could bear it away. It may be remarked that the apparently excessive
76 GEOLOGY OF THE NAERAGANSETT BASIN.
degradation of Iron Hill, as above noted, can be explained in this way.
It therefore seems reasonable to adduce ice work as one of the agents which
have served to bring about the destruction of the original to^^ographic reliefs
of this district.
Along with base-leveling and ice work, there is another class of agents
which have doubtless operated with much effect in bringing the district into
its planed-down state. These are the forces which act at and below the
level of the sea. There can be no question that the effect of the surf and
the shore currents is to plane off the rocks and to bring about such topo-
graphic conditions as are found in this basin. The only doubt is as to the
rate at which the work may go on. Judging by the speed with which the
benching action of the sea proceeds where the attack is delivered on hard
(i. e., undecayed) rocks, geologists have generally assumed that the aggre-
gate work which is due to this action is relatively small, that it plays no
important part as compared with base-leveling due to atmospheric agents.
We must remember, however, that what we know of the extent of super-
ficial decay in this and other countries requires us to believe that in the
oscillations of the continents it must often happen that deep sections of
rocks which have been made very friable are exposed to the mill of the surf
In this case it is fair to presume that they might be swe^jt away with some-
thing like the speed which is exhibited in the disintegration of the Pliocene
cliffs of Marthas Vineyard. When they face the open sea, these deposits,
in coherence comparable to the decayed beds of the Southern Appalachians,
are retreating at the rate of about 3 feet per annum, as determined by
fifty years' observations. At this rate the surf mill would be able to
work inward across the field of the Narragansett Basin in less than one
hundred thousand years.
CHAPTER lY.
ECONOMIC RESOURCES OF THE BASIN.
The economic resources of the basin inchide the soils, the pottery
clays, a limited range of bnilding stones, certain iron ores, and the coal
beds of the Carboniferous series.
SOILS.
The soils of this region, being in the main of glacial origin, have the
economic stamp of deposits which are more or less directly related to the
ice work. When, as is the case in the greater part of the district which lies
at more than 50 feet above the sea, as well as in much of the lower ground,
the soil rests upon bowlder clay, its fertility depends to a great extent on
the nature of the subjacent rock. If this be conglomerate, as is the case
over a large part of the central portion of the basin, the soil, because of the
generally insoluble nature of the detritus from these beds, is character-
istically lean. When it rests upon sandstones it is of moderate fertility.
Where, as in the region about Newport, and generally on Aquidneck
Island, the underlying rock is of shale, the soil is of more than usual value.
The considerable organic matter of these beds apparently serves to make a
richer field for the plants.
As compared with other portions of New England, this basin abounds
in glacial sand plains. These occupy the larger part of the surface below
the level of 50 feet above the sea, and a considerable area of higher-lying
ground. The relatively great extent of these plains seems to be due to the
fact that the existence of the extensive depression of the Narragansett Bay
made it the point of discharge of streams collected beneath the glacier,
which bore great quantities of debris beyond the retreating ice front and
deposited the sandy portion of this detritus in the shallow water of the sea,
which then covered the area. These sand plains are composed mainly of
siUceous materials, and afiford infertile soils. They are, however, of a quick
78 GEOLOGY OF THE NARRAGANSBTT BASIN.
nature, responding at once to manuring. Moreover, they are readily,
though temporarily, much improved by plowing in green crops, the store
of vegetable matter thus introduced into the earth serving to promote the
solution of the feldspar, mica, etc., which exist in the mass, though the quan-
tity is not considerable. These sand-plain soils, because of the absence of
bowlders, are easily tilled; they can at certain points be readily irrigated;
and they thus are likely in the modern time of intensive agriculture to be
valued more highly than heretofore.
The inundated lands of this district include a small area of marine
marshes and a considerable extent of fresh-water swamps. On account of
the limited range of the tides along this part of the coast, the reclamation
of the marshes can not be easily effected by diking. These areas will
therefore not receive further consideration. The fresh-water swamps,
including in this group all the lands which are made untillable by tempo-
rary flooding in the planting season, occupy an aggregate area of about
45 square miles, or nearly 28,000 acres. The larger part of this swamp
area is to a greater or less extent used as a source of water supply for
mills, the waste of the flood times being there stored for use in droughts.
Until this use of the swamps is abandoned it will not be possible to win
any large portion of these over-watered soils to agricultural use. About
one-third of the total area consists of bogs of limited extent, which do not
serve as reservoirs and are therefore open to improvement. In most
instances these fields can be readily drained by means of inexpensive
ditches. When so unwatered, the areas afford soils of two distinct groups.
Around the margins of each area there is normally a belt where the peaty
matter has not accumulated to a thickness of more than a foot, and where,
after being allowed to dry, and consequently to shrink, it can, by deep
plowing, be incorporated into the soil. In these portions of the drained
swamps tillable fields of very superior quality may be obtained. Within
the area of the basin there is probably a total extent of not less than 6,000
acres that is thus available for agriculture. Such ground is remarkably
well adapted to market gardening. When the peat of a drained bog much
exceeds a foot in thickness, it is difficult to reduce the area to ordinary tillage.
The only effective way of accomplishing this result is by securing condi-
tions of exceeding dryness by extensive ditchings, after which the peat may
be burned, as is done in northern Europe. In the present condition of our
COAL BEDS. 79
agriculture this method may be deemed inapplicable. Therefore the only
use which can be made of these bogs is for plantations of cranberries. In
the method of cultivation which is commonly employed with that plant,
several thousand acres of these drainable lands, especially the areas in the
eastern parts of the basin, are well fitted to this mode of tillage.
COALS.
The coal beds of the Carboniferous series afford the most important
economic resources of the basin. As is indicated in the portions of this
memoir which have been prepared by Messrs. Foerste and Woodworth,
these beds are probably limited to the lower half or shale-bearing portions
of the great section. So far as is known, no deposits of any importance
exist in the zone of the upper conglomerates. The exhibition of these coals
is the clearest in the region where they have been most extensively mined,
on the western side of the northern part of Aquidneck Island. At this point
they are seen dipping to the eastward near the surface at an average angle
of about 30°, with a diminishing slope as the workings penetrate toward
the center of the syncline. In this section at least two coal beds occur, the
lowest of which is about 2,000 feet below the base of the upper conglom-
erates, and the highest within perhaps 1,000 feet of that line.
In the western and northern parts of the basin the same or other coal
beds occur. Of these, the de230sits in or near Pawtucket and at Cranston
are the best known. The bed at Pawtucket — there seems to be but one —
lies apparently several thousand feet farther down in the great section than
the beds of Aquidneck. It is likely that this bed is continued southwardly
near the margin of the basin to near its southern end, and that the various
exposures which have from time to time been made along this line lie upon
it. It is also probable that the coal along the northern part of that border,
as far as Wrentham, is of the same or a closely related stratum.
The bed of coal in Cranston may most reasonably be regarded as
equivalent to one of those in the Aquidneck section. Its position in relation
to the upper conglomerates, however, can not be ascertained with any
certainty; so its place must be left in doubt.
The coal beds which were at one time worked in Mansfield are in such
a position that they can not be safely placed in reference to the other known
deposits. The relation of the beds to one another and to the immediate
30 GEOLOGY OF THE ^^ARRAGANSETT HASIN.
section in which they lie inclines the observer to the opinion that they are
the equivalents of the uppermost at. the mines on Aquidneck Island; but
this opinion has little evidence to support it.
Many other deposits of coal have been occasionally exposed in various
parts of the field in which the carbonaceous strata occur. Some of these,
as, for instance, the beds at Bristol, have been made the objects of experi-
mental mining. The last-named deposit is, from its position, to be reckoned
in the group occurring in the northern part of Aquidneck, but the greater
part of these little-known occurrences can only be placed as below the
upper conglomerate.
CONDITION OF BEDS.
As none of the coal beds of this district have been worked for many
years, the accounts of the deposits can not be made anew. The writer has
seen the bed which was last worked at the Aquidneck mines, and also that
at Valley Falls, which to within a few years ago was mined for "foundry
facino-s," and also that which was in a small way exploited at Cranston in
an unavailing effort to market it as fuel. From these observations and
the imperfect records which exist of the facts concerning the other deposits,
the following statements may be made as to the physical conditions of the
deposits.
The coal beds of this area probably number a half dozen or more, of
which only those of the Aquidneck group have been proved to have much
continuity. Owing to a feature which, so far as observed, they all present,
the thickness of none of these beds can be accurately determined. This
feature is the peculiar "rolling" to which the carbonaceous material has
been subjected in the dislocation of the beds of which it forms a part. In
practically all cases the beds above the coal have been by the process of
metamorphism brought into a very compact and rigid state. This change
appears to have taken place before or during the development of the folds
into which they have been cast. As the process of dislocation went on, the
irregular strains acting on the relatively little resisting coal caused it to
creep toward the points of least pressure. Tlae result was that wherever
the bed has been followed in the direction of the dip for a considerable
distance the layer is found to widen and contract, so that in a variable length
POSITION AND EXTENT OP COAL BEDS. 81
of from a few score to 600 or 800 feet it may pass from a mere trace to the
thickness of 20 feet or more, the cross section having a rudely lenticular
form. Followed horizontally, these thick portions of the vein thin toward
either end — at least that is the impression made by a study of the Ports-
mouth mine. So far as could be seen there, the horizontal dimension of the
lens was much greater than that shown in descending the slope. It is
evident that these conditions exclude any careful study as to the thickness
of the beds. It may be said that a rough computation of the contents of
the principal bed mined at Portsmouth showed it to be probable that the
thickness of the deposit before it was disturbed by the shearing action was
not far from 4i] feet.
It need not be said that this irregular form of the coal deposits, com-
bined, as it is, with a certain amount of faulting, which, though not dis-
tinctly shown in the small workings, is evident in the structure of the field,
makes it important to determine how far these features are general through-
out the basin. On this point the information is very scanty. It may be
said, however, that where, as in the Portsmouth mine, the workings had gone
for a distance of about 1,400 feet from the outcrop, and where the steepness
and the dip considerably lessened with the approach to the center of the
syncline, the irregularity of the bed had perceptibly diminished, giving
some reason to expect that there was an extensive area of coal in that cen-
tral part of the trough which had not been much dislocated. Unfortunately,
this is the only portion of the basin whei'e there is sufficient basis for reck-
oning that the coals within reach of mining work occupy a position which
gives them the chance of escaping the effects of "rolling-."
Owing to the lack of detailed knowledge concerning the position of
the coals, or even of the precise attitude of the rocks in this basin, it is not
yet possible to estimate with any approach to accuracy the area in which
coals of workable thickness may be found. It may be said in general that
all parts of the section lying more than 2,000 feet below the base of the
upper conglomerates show, from point to point, traces of coal. Consid-
ering the numbers of these chance ex^iosures, and noting the general way
in which the portions of the section containing coal are hidden by glacial
detritus, there is reason to believe that a considerable part of the rocks
below the indicated level are in some measure coal bearing. Definite
MON XXXIII 6
82 GEOLOGY OF THE ISIAERAGANSETT BASIN.
information as to the extent and thickness of these beds can not be had
without extensive and systematic exploration with the drill, but some results
could be obtained by well-planned superficial excavations.
It should be noted that, owing to the thickness of the barren upper
part of the section of the rocks in the basin, nearly one-fourth of its area
has the coal-bearing beds so deeply buried that they are below the level
where they could be mined; in much of the area the estimated depth
exceeds 10,000 feet. Moreover, nearly another fourth of this area is occu-
pied by the waters of the sea, so that it may be regarded as impracticable
to explore the underlying rocks. The remaining half is fairly open to
inquiry provided there should be found a market for coal of the peculiar
qi;ality which it affords, at a cost which would be imposed by its physical
and chemical conditions. These we will now note:
CHARACTERISTICS OF THE COALS.
Wherever found, the coal of this basin has certain characteristics which
distinctly separate it from any other fossil fuel that has been mined in
this country. The material is everywhere extremely anthracitic, often
ranging in appearance toward graphite. It is usually much penetrated by
veins of varied and rather complicated nature. It is high in ash, the pro-
portion commonly being 10 per cent, and often attaining to near twice that
amount. This ash contains in most instances a singularly large amount of
lime, which causes the cinders to smelt and thus clog the grate bars of a
stove or boiler furnace. As is shown by the accompanying analysis, the
percentage of fixed carbon is abnormally high, yet an extended trial of the
coal in producing steam showed that the value for this purpose was but 72
per cent of that of Lackawanna coal. The reason for this disproportion
may have been in part the lack of adaptation of the fire boxes to the
character of the fuel, which evidently needs a very strong draft, and the
fusible nature of the slag, which makes it difficult to keep the grate bars
clean. It is possible, however, that a portion of the carbon is in some
special chemical state which hinders its ready combination with oxygen,
perhaps in the condition of the supposed graphitic acid of Graham.
COAL ANALYSES.
83
Annli/ses of coal from the Portsmouth mine, Portsmouth, Rhode Island.'
[Analysts, Dr. F. A. Gooeh and Mr. B. T. Putnam.]
I.
II.
III.
IT.
V.
VI.
vn.
VIII.
IX.
Water
5.12
6.49
71.04
17.35
0.52
6.31
76.23
16.94
3.18
4.43
75.97
16.42
2.25
6.46
79.59
11.70
7.62
5.42
74.40
12.56
7.96
4.95
76.22
10.87
8.76
7.23
70.24
13.77
10.27
5.99
67.50
16.24
10.47
5.83
66.95
17.05
Volatile combustible . . .
Carbon
Ash . .
Sulphur
Ash
100. CO
0.216
Red.
10.94
100. 00
0.224
Red.
12.08
100. 00
0.258
Eed.
17.14
100. 00
0.643
Red.
12.32
100. 00
0.28
13.72
100. 00
100. 00
100. 00
100. 00
Red.
15.39
Red.
9.71
-'^^l-*Kv3?Sib.)-
11.26
11.48
I. Bottom of shaft, north side; thickness of seam, 3 feet 11 inches.
II. Bottom of shaft, south side ; thickness of seam, 2 feet 7 inches.
III. South side, 50 feet from bottom; thickness of seam, 6 feet.
IV. South gallery, 370 feet from bottom; upper three-fourths of 6-foot seam.
(Analyses I, II, III, and IV are from samples taken across the Tvidth of the seam.)
V. The average of seven analyses made from samples taken at intervals along the length of a
6-foot drill core, cut out of what is known as the "back seam," at about 90 feet below the
mouth of the Portsmouth mine.
VI and VII. The single analyses of this series showing the maximum and minimum percentages of
carb(m and ash.
VIII and IX. Samples taken from two lots, of several tons each, of freshly mined coal used in other
experiments.
Although it is probable that if the coal can be rained in the undisturbed
central parts of the shallower synclines it will there be found to contain less
vein matter, and hence will be lower in ash, its high percentage of the latter
and its other objectionable peculiarities may have to be reckoned as insu-
perable. It is therefore very doubtful whether it can ever be brought into
service for ordinary uses. The experiments heretofore referred to appear
to show that it can not be given a fair place for steaming purposes. The
fact that while the Portsmouth mine was working, the people of the neigh-
borhood were not willing to pay more than two-thirds of the cost of Penn-
sylvania anthracite for its product, shows that it is not well suited for house-
hold use. There remain, however, as before remarked, certain fields in
which this fuel may well find a jDlace. These are ore smelting, the manu-
facture of water gas, and the process of burning brick when the powdered
coal is placed between the layei's of the kiln.
' Notes on the Rhode Island and Massachusetts coals, by A. B. Emmons : Trans. Am. Inst. Min.
Eng., Vol. XIII, 1885, p. 511.
84 GEOLOGY OF THE NAERAGANSETT BASIN.
As to the first of the aforenamed uses, it may be said that the coal
of this basin seems to be fairly well suited to the needs of smelting.
It is low in sulphur; its specific gravity is so high that it will give a
large number of heat units for a given bulk; the ash, though high, is,
owing to its composition, easily smelted. I was told by the person who
owned the mine at Portsmouth the greater part of the time during which
it was worked, that the coal was the best that could be obtained for
smelting copper ores as well as for the subsequent working of that metal.
The further statement was made that a cargo of the fuel had been sent to
an iron furnace on the Hudson and that it proved very satisfactory as com-
pared with the anthracite of Pennsylvania in making" Bessemer pig. I was
also informed by one of the Crocker Brothers of Taunton, Massachusetts,
who worked the mine, that a test of a few tons of the coal had been made
in the manufacture of water gas and that it was well suited to the purpose.
It is not now possible to verify these statements, but they appear to be quite
consistent with what is known of the nature of the anthracite of this field.
The only imdetermined qualification of the Narragansett coals as
regards their use in the special arts above mentioned is that observed by
Dr. Arthur B. Emmons and described in the paper referred to. This, in
the words of the author, is " the striking peculiarity (hitherto unnoticed in
anthracite coals, or, I believe, in any coals) of quickly taking up a large per-
centage of water under a moist condition of the atmosphere and as readily
parting with it under a drier condition of the atmosphere." According to the
records obtained by Dr. Emmons and his collaborator, Dr. F. A. Gooch, the
Narragansett coal may, with the changes in the humidity of the air, vary as
much as 15 per cent of the whole weight of the material. How far this
peculiarity may affect the value of the coal in the smelter or water-gas
converter will have to be determined in an experimental way.
In considering the prospective value of this coal, the cost of mining it
is of course a matter of much importance. So far the practical experiments
in mining have been too few and too imperfectly executed to afford any
clear determination. The mine at Portsmouth, the only one in the basin
maintained in operation for any considerable time, was not well managed.
As the deep part of the pit was almost absolutely dry, the little water found
in it entering from the old upper workings, there was but slight expense for
pumping, the drip collected in the sump being hauled about once a month
EXPLORATION FOR COAL. 85
in one car. The roofs of the seam were admirably strong, requiring practi-
cally no timbering even where the pillars were robbed to a very extreme
point. At the time 1 last examined the place the best information which
could be had indicated that the cost of lifting the coal and treating it at the
breaker amounted to about $2.50 a ton. An estimate based on a suitable
amount of surface plant and proper approaches to the vein, with a fit admin-
istration, indicated that at the present price of labor the coal could be mined,
so long as the bed was in the then existing favorable position, for about one-
half the sum it was then costing. If the coal is found as a little-distorted
bed, averaging say 4 feet thick over as much as 3 square miles in the cen-
tral part of the basin, it should by means of vertical shafts be possible to
mine it at a yet lowej" cost than that named.
CONDITIONS OF FUTURE ECONOMIC WORK.
As to the best places for future exploration, it may be said that it
seems to be undesirable to undertake any further search for the coal at the
outcrops, the presumption and the evidence being alike in favor of the
opinion that at such places the coal, lying at a steep dip, is more likely to
be much infiltered with vein matter. The aim should be to seek the beds
in the central parts of the synclines, or where, though monoclinal, the strata
have a low dip.
The best of these places appears to be that in the northern part of Aquid-
neck Island. If the apparent diminution in the slope of the strata toward
the center of this trough be verified, there is a reason, before remarked, to
expect a considerable area of the coal beds in the central part of the north-
ern end of the island, where the rocks seem a little disturbed. There is no
very clear evidence as to the depth below the surface at which the coal may
li,e, but it seems quite probable that this depth is less than 1,800 feet in the
central portion of the area. To determine the true position of the deposits,
a line of borings should be carried across this part of Aquidneck Island in
a nearly east-west direction, with its western end about 600 feet from the
vertical plane where the old workings stopped. It will be well to supple-
ment the information thus gained, especially if the indications so obtained
are favorable, by other borings carried southward toward Quaker Hill.
The next most promising field for exploration is the belt of country
lying immediately to the east of the northward extension of the Providence
86 GEOLOGY OF THE NARRAGANSETT BASIN.
River, where, if the determinations of the sti'ucture as set forth in this
report are correct, the equivalents of the Portsmouth coal beds should be
found. The known facts go to show that in this part of the field the rocks
are not much disturbed, and that these coal beds are in the place where it
is supposed they should occur. Should these suppositions be verified,
there may be an area of 20 or more square miles in which the conditions
are favorable for mining operations. In connection with this part of the
field, it is necessary to set forth the facts concerning a boring made in the
town of Seekonk about twenty-five years ago. This gave a section of
the rocks which at its base appeared to indicate the occurrence of a bed
of fairly good anthracite at a depth of about 700 feet below the surface of
the ground. There can be no doubt as to the fact that the boring was
made. Abundant samples of the core were examined by the writer about
five years after the work was done. They were then in the possession of
the man on whose land the boring was made. They showed the rocks to
be of the general character of those which overlie the Portsmouth beds, and
also that the beds are not very much disturbed, the dip averaging not more
than 20°, probably to the eastward. An analysis of the coal showed it to
have the general character of the Rhode Island deposits, being extremely
anthracitic. Mr. Emmons, in the paper above referred to, states that, while
the boring down to the level of the coal is the result of an honest inquiry,
the coal is a fiction, the portion of the core showing the coal having been
made on the ground by operating the drill several times through a large
lump of coal brought by the disappointed explorer to the man who was
managing the apparatus, ostensibly to find whether the instrument would
cut a clean core in material of that degree of hai-dness. On review of all
the facts, it appears worth while to reopen this drill hole, which was carefully
plugged at the time the work was abandoned, and, Avith a reamer, to test
the bottom of the opening, in order to ascertain the truth. If coal is not
found, it will still be well to continue the drill work already done, down-
ward as far as it may be conveniently possible to do so, for the reason
that not far below the base of the present opening we may expect to pene-
trate the portion of the section where the beds of the Portsmouth district
belong. If the section could be carried to the depth of say 3,000 feet, the
information would be of great value as related to the possibility of finding
workable coal in the northern portion of tlie basin.
EXPLORATION FOE COAL. 87
By reference to the map (PI. XVII) it will be seen that the upper con-
glomerates occupy an insular position in the northern part of the basin, in
which they have been left by the degradation of the folds in which they lie.
So far as has been learned, there are no faults or other local disturbances
which should make it improbable that the beds equivalent to the Portsmouth
coal-bearing part of the section are found in their due place in the belt of
country on the north and east of this conglomerate area. It is to be noted,
however, that so far no coal beds have been revealed in this belt by natural
exposure or by chance excavations ; but this may be accounted for by the
fact that the district is much more deeply covered by the drift mantle than
that to the westward and northward. Therefore this section, within say a
mile of the margin of the upper conglomerates, may be regarded as next in
promise to the sections before mentioned as a field for explorations. It
should be observed that the angle of the dip toward the center of the
Taunton or Great Meadow Hill syncline (see figs. 8, 9, in Part II of this
monograph, pp. 122, 123) makes it probable that at a little distance within
the margin of the coarse conglomerates the coal beds which would lie in
the strata plane of those at Portsmouth would be greatly below the level
where they could be profitably worked.
As yet no adequate information has been attained which may serve to
show the conditions of the basin in the region to the east of the city of
Taunton. In that place a boring carried to the depth of 850 feet revealed
no good coal; indeed, but little more than carbonaceous matter was found.
The beds are presumably the equivalent of those which, in a thickness of
2,000 feet or more, overlie the coals of the Portsmouth mines. The churn
drill gave, of course, no information as to the attitude of the rocks. It
seems likely that there are but slight faults or folds in this part of the field,
and that in the main the beds belong to the section which may be expected
to contain coals.
For the reasons before given, which go to show that it is not worth
while further to explore for coal around the margins of the basin, there
remains only one other portion of its area to consider. This is the field
between Aquidneck Island and the western shore of Narragansett Bay. The
greater part of this district is covered by water. All that part of it which
lies to the south of the northern end of Canonicut Island is evidently so
affected by regional metamorphism that any coal which it may contain is
88 GEOLOGY OF THE NAEEAGANSETT BASIN.
likely to be of very poor quality. The water-covered area is, as before
noted, difficult to explore. If, however, coal should eventually be found
beneath those arms of the sea, it could doubtless be mined with safety,
though with added cost, on accoimt of the difficulties of access.
Before any further costly effoii to develop the coal deposits of this dis-
trict is made the coal from some one of the openings — that at Portsmouth,
for instance — should be subjected to systematic and thorough experiments
to determine its value in the wide range of arts to \vhich this fuel may be
applied. These tests should include at least the arts of ore smelting and
the manufacture of water gas, brick, and pottery. Experiments, which on
theoretical grounds appear to be very promising, should be made in crush-
ing and washing the coal and in subsequently converting it into briquettes.
It may be found that in this form the material will prove ser^aceable as an
ordinary fuel. There can be little doubt that this inquiry should be under-
taken. As before noted, there is a very large amount of coal in this basin,
although there is no basis of reckoning the total quantity with any approach
to accuracy. There can be little doubt that it is to be estimated by the
hundred million tons. Even though, as has been assumed, this coal can not
compete in ordinary uses with that which is imported, the chance that it
may serve in many important arts affords full warrant for a careful stud}^ of
its quality and distribution.
The inquiry above noted could be undertaken on a lesser scale, lim-
iting it to the Portsmouth field. As already stated, this is a typical area,
probably the best in the basin. Work there should first be directed to
ascertaining the extent, condition, and depth at which the coals occur
in the central portion of the trough in which they lie. If the results
obtained are satisfying, it will be easy to obtain from the existing openings
enough coal to make the trials which have been suggested. Supposing
these tests to show economic value, the old workings should be abandoned
and the beds approached by means of a vertical shaft, so placed as to enter
them as near as possible to the center of the basin.
IROlSr ORES.
The iron ores on the western border of the Narragansett Basin have
a certain amount of economic interest, in that, in case the coal is ever
developed, they may become of value for the purpose of mixing with the
FUEL FOR SMELTING. 89
ore brought from other parts of this country or from abroad. The only
iron ore of promise in this field is that which occurs at the eminence known
as Iron Hill, which lies in the town of Cumberland, about 2^ miles east from
Woonsocket, Rhode Island. The deposit is a rather ilmenitic magnetite,^
containing about 35 or 40 per cent of metallic iron, but it is remarkably free
from phosphorus, in this regard closely resembling the best Swedish ore,
which it also resembles in its petrographical characters. The mass of the
ore, apparently in its nature a dike, runs along the general surface of the
country in which it lies, to the height of nearly 100 feet. It has a width
of about 600 feet and is of about twice that length. It is probably con-
tinued downward to an indefinite depth, and may extend for a considerable
distance beneatli the cover of drift to the north and south, in which axis
the mass seems to trend. The mass of ore may therefore be reckoned as
large; it probably could afford, if desired, a total of 10,000,000 tons or more
without particularly deep workings The limestones of Lincoln, Rhode
Island, between Iron Hill and the western margin of the Carboniferous rocks,
afford an excellent flux. As they appear in the form of white crystalline
marble, it is probable that they also are nonphosphatic. Thus, if the coal
of the Narragansett Basin proves to be as useful as a smelting fuel as it
promises to be, the shores of the bay may prove to be well equipped for
the manufacture of pig iron.
About twenty-five years ago the coal from the Portsmouth mines was to
a certain extent used in smelting copper ore which was mainly brought from
South America. It was stated when this process was in operation that the
fuel was satisfactory. If this was the case, there is yet another reason for
supposing that the coal of this basin has a value when used in the reduc-
tion of metals. As a whole the evidence thus points to the conclusion that
those who undertake to bring these coals into the market will do well to
look carefully into the question of their adaptation to this use. If this
element of value could be verified, the basis for the development of the
deposits might be found without reference to the other ends to which their
product might be applied.
In closing these remarks concerning the economic values of mines in the
Narragansett Basin, it may be said that, as far as the coal beds are concerned,
' See A microscopical study of the iron ore or peridotite of Iron Mine Hill, Cumberland, B. I.,
by M. A. Wadsworth: Proc. Boston Soc.Nat. Hist., Vol. XXI, 1883, pp. 194-197.
90 GEOLOGY OF THE NARRAGANSETT BASIK
the developments are not sufficiently advanced to enable the geologist to
prove very helpful to those who desire to exploit its resources. Such
indications as are here given are therefore to be regarded as suggestions
rather than as definite recommendations; the latter can be safely made
only when accurately determined facts, such as are obtained from extensive
workings, have been gathered.
GEOLOGY OF THE NARRAGANSETT BASIN
Part II.— THE NORTHERN AND EASTERN PORTIONS
OF THE BASIN
A BIBLIOGRAPHY OF THE CAMBRIAN AND CARBONIFEROUS
ROCKS OF THE BASIN
By JAY BA.CKXJS ^VOOJD^^^ORTH
CONTENTS.
Page.
Chapter I. — The problem of stratigraphic succession 99
Repetition of lithologieal characters 100
Transition of lithologieal characters 100
Effects of igneous intrusions 101
Metaraorphism 101
Folding and faulting 101
Denudation 101
Glaciation 102
Submergence 103
Absence of artificial excavations 103
Chapter II. — The pre-Carboniferous rocks 104
Algonkian period 104
Blackstone series 104
Cumberland quartzites 106
Ashtou schists 107
Smithfield limestones 107
Cambrian Period 109
Lower Cambrian 109
Middle Cambrian (unrepresented) 109
Upper Cambrian 109
Silurian Period (unrepresented) 113
Chert pebbles 113
Chapter III. — The igneous rocks of the border of the basin 114
Granitic rocks 114
Plympton felsites 116
Granite-porphyry 117
Other rocks 117
Gabbro hills of Sharon 118
Chapter IV. — The Carboniferous basin 119
General structure of the basin 121
Maps of the boundary of the basin 124
Boundary of the basin on the north and east 125
From Cranston to the Blackstoue River 125
From Blackstone River to Sheldonville 127
Connection between the Narragansett and Norfolk County basins 127
Sheldonville cross fault 127
From Sheldonville to Foolish Hill 127
Foolish Hill fault 128
From Foolish Hill to Brockton 128
From Brockton to the North River 129
Shumatuscacant fault 129
From North River to Lake ville 129
From Lakeville to Steep Brook 130
Inliers 130
North Attleboro inlier 131
Nemasket granitite area 131
Summary 131
94 CONTENTS.
Chapter V. — The Carboniferous strata 133
Determination of horizons within the basin 133
Means of determining superposition 133
Tabular view of the strata in the Narragansett Basin 134
Formations below the Coal Measures 135
Pondville group 135
Basal arkose beds 135
Foolish Hill exposures 135
North Attleboro exposures 135
Pierces Pasture in Pondville, Norfolk County Basin 135
Absence of basal granitic conglomerates 136
Geographical conditions indicated by the basal arkose 137
Absence of iron oxides in the basal arkose 138
Absence of carbonaceous matter along northern margin 139
Extent of arkose zone 139
Suprabasal conglomerates 140
Millers River conglomerate 140
South Attleboro exposure 140
Jenks Park exposure in Pawtucket 141
Wamsutta group 141
Eed rock areas 142
Area along the northern border 143
Gray sandstones of the northern border 144
North Attleboro area 145
Conglomerates 146
Sandstones 147
Shales 147
Central Falls area 147
Pawtucket area 148
Eed beds in Attleboro, Eehoboth, and Norton 148
Norfolk County area 148
South Attleboro limestone bed 149
Attleboro sandstone 151
Igneous associates of the Wamsutta group 152
Diabase 152
Quartz-porphry group 153
Diamond Hill quartz mass 155
Wamsutta volcanoes 155
Folding of the Wamsutta group 156
Flora of the Wamsutta group 158
Coal Measures 159
Cranston beds 159
Providence area 159
Pawtucket shales 162
Sockanosset sandstones 163
East Side area in Providence 163
Tenmile Eiver beds 164
Lebanon Mills exposure 164
East Providence area 164
Leonards Corner quarries 165
Section from Watchemocket Cove to Riverside 165
Halsey Farm section at Silver Spring 166
Exposures in Seekonk 168
Hunts Mills section 169
Perrins anticline 169
Bored well near Lebanon Mills 170
CONTEJSTS. 95
Chapter V. — The Carboniferous strata — Continued.
Coal Measures — Continued. Page.
Seelionlibeds 173
Seekonk conglomerate 174
Beds north of the Tenmile River in Attleboro , 17.t
Contact of red and gray beds, with local unconformity 176
Red shales 177
Raindrop imprints 178
Attleboro syncline 179
Blake Hill fault block , 180
Fossils '. 181
Coal 182
Blake Hill thrust plane 183
Dighton conglomerate group 184
Extension of the Coal Measures north and east of Taunton 187
Dedham quadrangle 187
Mansfield area 1S8
Flora of Mansfield section 191
Bridge water area 192
Abington quadrangle 193
Taunton quadrangle 195
Red beds 195
Outcrops in Norton 195
Winneconnet ledges 196
Scolithus beds 197
Taunton waterworks section 198
Westville section 199
Taunton River Valley 200
Middleboro quadrangle 200
Chapter VI. — Organic geology 202
Insect fauna 202
Stratigraphic position of the fauna 203
Odontopteris flora 203
List of plants identified by Lesquereux 204
Coal beds 205
Search for coal 207
Thickness of the Carboniferous 208
Acknowledgments 211
Appendix. — Bibliography of the Cambrian and Carboniferous rocks of the Narragansett Basin. . 212
ILLUSTRATIONS
Plate II. Pre-Carbouiferous rocks at western border, near Providence, Rhode Island 12G
III. Plant-bearing outcrop of Wamsutta group in North Attleboro, Massachusetts 146
IV. Faulted diabase dikes in North Attleboro, Massachusetts 152
V. Rocky Hill, Providence, Rhode Island, a glaciated ridge of the Carboniferous 162
VI. Carboniferous sandstones at Silver Spring, Rhode Island 166
VII. Carboniferous sandstones near Attleboro, Massachusetts 176
VIII. Medium-sized conglomerate, Attleboro, Massachusetts 176
IX. Ripple-marked vertical sandstones, Attleboro, Massachusetts 178
X. Raindrop imprints on vertical strata, Attleboro, Massachusetts 178
XI. Plainville Valley, Wrentham, Massachusetts 180
XII. Vertical bed of Dightou conglomerate at Attleboro, Massachusetts 181
XIII. Near view of Dighton conglomerate, Attleboro, Massachusetts 184
XIV. Selected waterworn and indented pebbles from Dighton conglomerate, Attleboro,
Massachusetts _ 186
XV. Vertical Carboniferous sandstones, Plainville, Massachusetts 186
XVI. General view of surface at AVest Mansfield, Massachusetts 188
XVII. Geological map of the northern and eastern portions of the Narragansett Basin . . 210
Pis. 3. Diagram showing misleading synclinal exposures of similar strata 102
4. Exposure of disconnected dike in Lime Rock quarries, Rhode Island 108
5. Sketch map of distribution of upper Cambrian pebbles 110
6. Map showing distribution of metamorphosed Carboniferous rocks 120
7. Map showing general outline of the Narragansett Basin _ _ 121
8. Section across eastern arm of the basin 122
9. Outline map and general cross section of the northern jiart of the basin 123
10. Edward Hitchcock's cross section of the Carboniferous area 123
11. Map showing distribution of red sediments 142
12. Geological section northward from Robinson Hill 145
13. Diagram showing disappearance of Wamsutta group in the Coal Measures.. 148
14. Section through felsite knob in Attleboro, Massachusetts 153
15. Geological section in the Millers River region 156
16. Geological section in the Arnolds Mills region 1.57
17. Hypothetical geological section east and west through Providence, Rhode Island 160
18. Folded and faulted Carboniferous shales at Pawtucket, Rhode Island 162
19. Sketch of zone of excessively jointed sandstones, face of McCormick's quarry 166
20. Geological section from VVatchemocket Cove to Riverside, Rhode Island 166
21. Geological section through rocky islets at Halsey Farm, Silver Spring, Rhode Island .. 167
22. Geological section of rocky headland near Silver Spring, Rhode Island 168
23. Theoretical section of folded structure on western margin of the Narragansett Basin.. 169
24. Contemporaneous erosion with unconformity in the Carboniferous at Attleboro,
Massachusetts 176
25. Diagram showing cross bedding 178
26. Geological section of Plainville Valley and thrust plane 183
27. Section of the Mansfield Coal Measures igo
28. Geological section in "Westville, Massachusetts 199
29. Diagram illustrating the case where boring affords a satisfactory test for coal beds 208
30. Diagram illustrating the case where trenching affords a satisfactory test for coal 208
MON XXXIII 7
97
Postscript. — After the pages for this monograph were cast, the writer
found in shaly strata opposite Plaiuville Station, at the base of the fault
block described on page 183, the footprints of a small vertebrate, probably
an amphil^ian, associated with rain prints and mud cracks. — J. B. W.
GEOLOGY OF THE NARRAGANSETT BASIN.
PAET II.-THE NORTHERN AND EASTERN PORTIONS OF
THE BASIN.
By J. B. WOODWORTH.
CHAPTER I.
THE PROBLEM OF STRATIGRAPHIG SUCCESSION.
In the autumn of 1894 the writer was assigned the task of reporting
upon the stratigraphic succession of the Carboniferous deposits in the Nar-
ragansett Basin. Previous to this time, during the summer months of 1891
and 1892, he had made an examination of portions of the basin which
seemed likely to afford a key to the structure of the beds. In the autumn
of 1894 and during the field season of 1895 the examination of the field
was continued. The following pages set forth the results of these studies.
While more was effected than the writer personally expected, there are
many questions yet to be determined regarding the equivalency and thin-
ning out of strata and the tracing of horizons. It is believed that the
work so far accomplished serves to afford, first, a truer measure of the
thickness of the beds than has heretofore been gained; second, a nearly
complete analysis of the structure of the part of the basin studied; and,
third, a differentiation of the beds into a few horizons which have a
geographical value, if not also in most cases a local chronological value.
The opportunity which the geologist has of determining the succession
of the strata in any region usually increases with the amount of uplift and
denudation, since, were the beds of a basin to remain in the condition in
which they were deposited, the surface of only the topmost stratum would
be open to examination. However, if uplift and denudation proceed so far
100 GEOLOGY OF THE XARRAGAXSETT BASIN.
as to produce excessive complication of structure on the one hand and
to remove great thicknesses of strata on the other, the evidence which
the geologist seeks for the reconstruction of ancient deposits may be too
scanty to permit him to obtain satisfactory results. The stratified rocks of
the Narragansett Basin long since ceased to lie in their original attitixdes,
and so mixch of them has been carried away by erosion that their strati-
graphic succession can be made out only with difficulty and only for limited
portions of the field. But these general causes, which, by reason of their
long-continued action or their intensity, have worked to the detriment of
geological investigation in most mountain-built districts, have in this field
been reenforced by local peculiarities arising fi'om the geographical position
of the area and from events of recent geological occurrence.
The difficulties encountered in making out a complete and satisfactory
succession of the strata of this field may be stated as follows:
REPETITION OF LITHOLOGICAL CHARACTERS.
The duplication in texture and color of sediments widely separated
chronologically, but in close juxtaposition, either by superposition through
unconformable deposition or by folding and faulting, is a source of doubt
where fossils are not present in both terranes. Thus, in North Attleboro,
Massachusetts, and northward, in the midst of an area occupied by red
Carboniferous shales, sandstones, and conglomerates, there appear red
Cambrian shales not to be differentiated in most localities except by means
of the contained fossils. Until Cambrian fossils were discovered, the red
Cambrian strata were included by all observers with the red series of more
recent date.
TRANSITION OF LITHOLOGICAL CHARACTERS.
By gradation in the size of the particles in a stratum, a conglomerate
on one side of a denuded anticline or syncline may be represented by a
sandstone or shale on the other side of the same broad fold. In like man-
ner, the coloration of beds may vary from one part to another of the same
basin, so that strata are no longer distinguishable. In the northwestern
part of the Nari-agansett Basin there are thick beds of red color, having a
fairly well defined stratigraphic position. Farther south these beds are
replaced by others of dark-gray color, and are even underlain by kinds
of beds which in the northern area always overlie the red series.
LOCAL CONDITIUNS AFFECTING OBSERVATION. 101
EFFECTS OP IGNEOUS INTRUSIONS.
Igneous intrusions, by inducing litliological changes, often render the
determination of the equivalency of the altered strata a work of much
labor, particularly where the alteration is but one of several obstacles to
the tracing of the stratigraphy. Where, owing to unfavorable conditions
at the present surface, the contact of igneous rocks with stratified rocks can
not be observed, much perplexity often arises as to the order of events.
METAMORPHISM.
Dynamic metamorphism has changed both the texture and the colora-
tion of the rocks of extensive sections, thus masking the original sedimen-
taiy characters and rendering the recognition of horizons, either by fossils
or by litliological peculiarities, difficult. Thus the Carboniferous strata
from Wickford north to Providence are highly metamorphosed, while beds
of the same age northeastward in the basin are very much less changed
from their original condition. Ottrelite-schists in the former area pass into
shales in the latter region.
FOLDING AND FAULTING.
While folds and faults directly aid investigation by bringing to the
surface strata which would otherwise be concealed, the complete inversion
of beds and the separation of blocks of strata by faulting result in con-
fusion. In the series of red strata which occur in North Attleboro the
utmost complication has arisen through the degree of folding; and here,
also, a block of strata of one series has been thrust into a position where
it is surrounded by beds of a different horizon.
DENUDATION.
Where beds are correlated from fold to fold by ph^'sical indications,
such as the repetition of like beds in the same order and with the same
topography, without the aid of fossils, denudation succeeded by local
concealment of parts of the series by deposition may lead to erroneous
conclusions in the matching of beds. In this basin there is a group of
conglomerates found onl}^ in synclinal areas; at lower horizons are other
conglomerate beds. If denudation should halt upon one of these lower
beds where it is exposed in the axis of a syncline, doubt would arise,
102
GEOLOGY OF THE NARRAGANSETT BASIlSr.
Fig. 3.— Diagram showing misleading synclinal exposures of similar strata.
without otlier means of , correlation than these physical criteria, as to which
horizon formed the axis of the synclinal structure. Where beds have been
stripped off from areas several miles in width, as between the Narragansett
and Norfolk County basins,
._ \ ,,.- --,, there is difficulty in making
W y' y-'" ""■-•-, "\ /' correlations. Owingtodenu-
''\ " ,--'' ■-., \ /' / dation, the uppermost beds
,--'' ,.- ~,_ '"-.^ '-., '\ ,.-' .,''' of a formation, as originally
deposited, may be entirely
lost. Thus there is doubt
as to the correlation of the
upper conglomerates near
Newport with those in the
Taunton syncline. The Newport conglomerates may be in the position of
the left-hand syncline in fig. 3, while those near Taunton correspond to the
upper conglomerate in the right-hand svncline.
GLACIATION.
The chief difficulty arising from g-laciation is the coating of drift
which is left upon the rocks of a country. In the Carboniferous tield of
southern New England the embarrassment from this source is particularly
great, for the reason that the area received a thick coating of the deposits
of the retreating ice sheet. So effectuall}- are the bed rocks concealed in
parts of the Carboniferous basin, that outcrops may not be seen oftener
than from 3 to 6 miles in any direction. The tracing of highly inclined
strata along tlieir strike can not be safely undertaken in these areas,
and the mapping of the formation must be done with reference to the
broadest possible groups, or perhaps be limited to the indication of the
presence of undiscriminated members of a large rock senes. The distri-
bution of frag'ments of rock along known lines of glacial carnage is some-
times a help in fixing the boundaries of the underlying bed rocks.^ In this
field the transportation of bowlders was from north to south. Where the
rocks trend in bands from east to west, the line along which each differ-
ent kind of rock appears in the drift is approximately the boundary line
' See Fence- wall geology, by A. F. Foerste : Am. Geol., Vol. IV, 1889, pp. 367-371.
LOCAL conditio:ns affecting observatiok 103
between it and the band of rock next north. Where the strata strike in a
northerly direction, the fanning- out of the drift southward makes the deter-
mination of less value; but trains of bowlders thus formed are frequently
of g-reat use in checking observations upon isolated outcrops. In using
this method less reliance is to be placed upon waterworn drift than upon
ice-laid deposits.
SUBMERGENCE.
Recent depression of the land has, in the immediate vicinity of
Narragansett Bay, caused the flooding of old valleys, so as to isolate rock
areas in the form of islands and to conceal strata which might otherwise be
open to examination. To a certain extent this difficulty is compensated by
the good exposures in the cliffs formed along the seashore by the action of
waves. Such natural sections occur around most of the islands in the bay
and along the coast where hard rocks come to the surface, as far north as
Providence.
ABSENCE OF ARTIFKJIAL EXCAVATIONS.
The almost complete absence of artificial openings, either mines or
quarries, in this field at the present day has limited the observations here
detailed almost entirely to surface exposures. The quarries which exist
are mostly in the granitic rocks bordering the basin, and it is only from the
recorded observations of previous workers that information regarding coal
mines can be obtained.
It is only by a recognition of these difficulties and their combinations
at various localities in this field that the geologist realizes the checks which
it is necessary to apply to his work in all stages of its advancement.
These difficulties, along with a formerly jDrevailing misapprehension as to
the nature of secondary structure in rocks, are responsible for the general
belief among geologists that the strata of this area are too much broken to
be unraveled. On taking some of the earlier-drawn sections of the strata
of this basin into the field, it will be seen that over considerable areas
cleavage was mistaken for stratification, metamorphosed Carboniferous
beds were taken for schists of much earlier date, the dips of strata were
averaged where they should have been analyzed and separately repre-
sented, and more reliance was placed on identity of color than this feature
is worth in determining the identity of origin of sediments.
CHAPTER II.
THE PRE-CARBONIFEROUS ROCKS.
ALGOXKIAK PERIOD.
BLACKSTONE SERIES.
Primary (limestone and hornbleurte rocli). C. T. Jaclcson: Report on the Geology and Agriculture of
Rhode Island, 1840.
Taeouic (Stockbridge limestone, etc.). E.Emmons: Agriculture of Ne-n' York, Vol. 1, 18i6, pp. 90-93 ;
also American Geology, Vol. 1, 1855, p. 22.
Moutalban. W. O. Crosby : Geology of Eastern Massachusetts, 1880, p. 128.
Pre-Cambriau (Hurouian?). N. S. Shaler: Bull. Mus. Comp. Zool. Harvard Coll., Vol. XVI, 1888,
pp. 15-18.
The above-named writings, with their chronological references, as
made at the date of the respective papers, set forth in a word the views
advanced regarding the age of the series of limestones, chloritic and horn-
blendic schists, slates, and quartzites, wliich occur in the lower portion of
the Blackstone Valley and near Providence, within the limits of Rhode
Island, along the western border of the Carboniferous basin. It evidently
has been the common opinion of geologists that these rocks are older than
the Paleozoic series The names here introduced, without a geological
map, are intended as locality terms only.
The Carboniferous strata of this basin rest everj^where unconformably
on older rocks, which are found immediately bordering the basin or as
small inliers within its limits. These inliers are Cambrian sediments, with
associated igneous rocks. The pre-Cambrian or Algonkian rocks above
referred to as the Blackstone series occur in the form of highly inclined
masses of strata separated and penetrated by granitic intrusions or bath-
olites. The area of these clastic and the associated igneous rocks, now
exposed at surface along the western border from Cumberland southward
in Rhode Island, is about equally divided between the two groups. The
thorough disruption of these ancient strata by changes of attitude and
igneous intrusion has produced in the area a type of structure which may
104
THE BLACKSTONE SERIES. 105
well be termed a batliolitic complex. Notwithstanding the irregular dis-
position of the detached masses of strata, there is traceable a dominant
structural system in this belt which is nearly east and west in its trends.
The strikes of the strata in the Blackstone Valley are NW.-SE.; those
in the area west of Providence, nearly E.— W. Members apparently of an
equally ancient system of rocks occur on the southeast of the basin in the
gneisses and schists of the New Bedford area (see fig. 7, p. 121), and in
small masses near Canton Junction.
The geological relations of the Blackstone series are not exactly
defined along the northern and western border. The lowest stratified
member along this border of the basin has not been seen, in the area under
discussion, to rest on the necessarily older land mass from which it was
derived. This separation is probably due to the intrusion of granitic
masses.
The determination of the pre-Cambrian age of the group of limestones,
schists, slates, and quartzites, in the Blackstone River area, rests upon the
relation which it bears to the lower Cambrian sti-ata in North Attleboro.
The Olenellus fauna occurs in little-altered, red, calcareous shales and slates
at this latter place in close proximity to granite (hornblendic granitite).
Four miles west of this inlier of the Carboniferous area occur the sedi-
ments involved in the complex already described. These strata are higlily
altered sediments, now hornblendic and chloritic schists, mainly of a green
color, altered sandstones or quartzites, and crystalline limestones. The
presumption that these rocks are pre-Cambrian rests, at present, therefore,
on the difference in metamorphism between them and the lower Cambrian
rocks in the same field. The criterion apjsealed to in this case is embodied
in the statement that where two sets of rocks coexist in the same dynamic
field, that group which has undergone one dynamic movement more than
the other is the older. If this view is maintained, this series of rocks falls
into the Algonkian. Evidence of unconformity with the lower Cambrian
is necessary to make this conclusion positive. The relation of the granitic
intrusives to the pre-Cambrian on the one hand and to the Cambrian on the
other is simply to show that the granitite is younger than the former, and
that the sedimentary rocks are of different ages.
From the typical development of this series in tlie lower course of the
Blackstone River between Woonsocket and Pawtucket, it is here proposed
106 GEOLOGY OF THE NAREAGANSETT BASIN.
to refer to the rocks, exclusive of the igneous intrusives, as the Blackstone
series. On hthological grounds, which have some support in the stra-
tigraphy, the series may be divided into the Cumberland quartzites, the
Ashton schists, and the Smithfield limestones.
CUMBERLAND QUARTZITES.
Bands of quartzite occur as discontinuous outcrops at several localities.
The principal of these is traceable from the southern side of Sneech Pond,
along the main street southeastward for a mile and a half in the village of
Cumberland Hill. The width of outcrop varies from 500 to 1,500 feet.
Another small exposure occurs on the same general trend 2 miles north of
Ashton. A broad belt of outcrops of the rock occurs in the valley of the
Blackstone from Cumberland village southeastward. The quartzite is
interbedded with schists or green slates in alternations of varying thickness.
The dip of the structure is NE. at angles from 50° upward.
At Albion Mr. F. C. Schrader has observed fragments of the quartzite
in a siliceous and quartzitic schist striking about N. 41° W. and dipping
50° NE. Just Avest of this outcrop, and separated from it by a small ravine,
is a large outcrop of the quartzite. The presumption here is that of an
unconformable relation of the Ashton schists upon the quartzite. The
quartzite is lithologically the same as the Cumberland rock. The fragments
of the quartzite in the Ashton schists are sometimes somewhat worn. The
schist in the bold bluff on the east of Sneecli Pond also contains small,
rounded, and broken fragments of the quartzite. These facts, together
with the siliceous character of the slates and schists, indicate that they were
derived from the erosion of a quartzite terrane. Some evidence of probable
unconformity of dip at the Albion locality also points to the conclusion
that the more massive quartzite beds of the Blackstone series are older
than the Ashton schists.
Limited exposures of quartzite occur along the border in the western
part of Providence at Manton. The quartzites are prevailingly brownish-
yellow in color wherever they occur, are generally granulated by crushing,
and are glossy by reason of the development of some sericite. Their
occurrence in lenses and along strike lines, together with the probability
that they are older than the Ashton schists, seems to indicate that the
THE BLACKSTOI^E SERIES. 107
exposures at the present surface are due to the truncation of close-pressed
folds in which the quartzites occupy anticlinal axes.
ASHTON SCHISTS.
Reasons have been advanced above which make it probable that the
argillaceous rocks of the Blackstone series are the finer sediments succeed-
ing the deposition and partial erosion of the Cumberland quartzites. Dis-
tinctions in the several broad bands of these rocks may be based upon the
prevalence of siliceous sediment on the one hand and of the chloritic and
hornblendic metamorphic products on the other. Not less manifest are
differences of secoiidary structure, on which the slaty and schistose char-
acter of the beds in many places depends. All along the border of the
area, where the rocks are in contact with granitite and quartz-porphyry,
zones of local metamorphism occur in which the characteristic effects of
igneous intrusions are to be observed. The series as a whole is character-
ized by its greenish color. Some of the rocks included in the schists are
jDrobably of igneous origin.
SMITHFIELD LIMESTONES.
Owing to the setting off of Lincoln from Smithfield in 1871, the areas
of limestone formerly designated by the name here used are no longer in
the town of that name. The areas of this rock are isolated, ovoidal in out-
line, and have no very systematic distribution. In the main, they lie near
granitic masses, as between the valleys of the Blackstone and Moshassuck
rivers. The areas are a mile or more apart. Those in the area referred to,
including Lime Rock, are in general along the same horizon in the Black-
stone series. Most of the areas are in the Blackstone Valley, but there are
other outcrops south of the Smithfield granitic mass, in North Providence
and Cranston.
The limestone are finely granular, dolomitic, crystalline aggregates,
and have a laminated structure. Shear zones with development of chloritic
minerals are common. The rocks have been subjected to extensive shear-
ing and crushing movements, with the consequent faulting of small dikes,
as in the Lime Rock quarries. The limestone occupying the space between
these dismembered dikes shows to the eye no trace of the separation. Tlie
108
GEOLOGY OF THE NAREAGANSETT BASIN.
disjoined parts of a small dike of ampliibolite/ probably altered diabase,
had, ill 1887, the appearance shown in the accompanying diagram (fig. 4).
The contact relations of the limestones with the schists which inclose
them have not been satisfactorily determined, by reason of the lack of good
exposures. So far as the evidence yet obtained goes, the limestones appear
to be of sedimentary origin, though no trace of fossils has been found in
them. The lack of continuity in the exposures is probably due to com-
pressive movements in the formation of a closely folded series. It is
probable that the ovoidal form of the outcrops as represented on maps
would have to be made eUiptical, or even pointed at the ends, if better
exposures existed.
On the hypothesis of close folding, which alone can account for the
great breadth of outcrop of this
series on the western side of the
Carboniferous basin, the thicker
limestones, if newer than the slates,
would fall in synclinal axes.
In the bed of a small brook
above the old iron mine in Crans-
ton a vertical bed of limestone may
be seen between the beds of slate.
The limestone has a thickness of
about 10 feet. It here seems to be an intercalated bed. As yet no facts
have been discovered to show whether the limestones are of the same age as
or newer than the slates and schists. It is clear that some of the limestones
are not older than the argillaceous series.
The most conspicuous feature of the limestone areas is the occasional
association with them of metalliferous deposits. The richest and most
-Exposure of discoimected dike
Rhode Island.
Lime xlock quarries,
1 Amphibolite from Lincoln. This rock occurs in the southernmost limestone locality at Lincoln,
Ehode Island. Microscopic characters : Hornhlende occurs in the slide, with extinction parallel to
shorter diagonal of rhombs. Chlorite is present in large quantities. Muscovite occurs in confusedly
arranged irregular lamina?. Titauite occurs in cleavage forms, derived probably through leucoxene
from decomposition of titaniferous magnetite. Magnetite in some areas still exhibits a kernel of the
unaltered miueral. Apatite occurs partly or wholly iuclosed by the titanite. The highly altered
condition of this rock renders its determination doubtful. Quartz occurs in small areas, where it is
probably of secondary origin. Notwithstaudiag the abseuce of the feldspar constituent, the nature
of the hornblende makes it probable that the rock, now an amphibolite, was originally a diabase, like
many other highly altered dikes in southern New England.
Mr. Schrader reports other dikes near the western margin of the Blackstone series in the valley
of the Moshassuck River. There are also in this field apophyses from the granitic rocks.
UPPER CAMBRIAN PEBBLES. 109
varied of these is in the northern part of the town of Cumberland, where,
in the area about Sneech Pond, ores of copper and iron occur, rephxcing
portions of the Hmestone, angular brecciated fragments of which lie in
the ore-bearing mass. The iron of the old mine in Cranston, in the "dug-
way," is probably a ferruginous replacement of the limestone. The Sneech
Pond ore bodies above mentioned are near eruptive rocks, but whether the
deposits have originated through the action of heated waters or through the
downward percolation of acidulated surface waters, the field itself does not,
in the present condition of the openings, give opportunity for determining.
CAMBRIAK PERIOD.
LOWER CAMBRIAN.
Rocks comprised within the limits of the formations now denominated
Cambrian were referred to vaguely as early as 1844 by Ebenezer Emmons,
but the discovery of demonstrable Cambrian strata in this field was not
announced until 1888, when Professor Shaler and Dr. A. F. Foerste pub-
lished the account of the fossils found by them in North Attleboro, Massa-
chusetts. For a further notice of these rocks the reader is refen-ed to Dr.
Foerste's description in Part III of this monograph.
MIDDLE CAMBRIAN.
Beds of Middle Cambrian age have not been discovered south of the
area about Weymouth and Braintree, where they are known to occur.
UPPER CAMBRIAN.
{Not known in place.)
Postdam. W. B. Kogers: Proc. Boston Soc. Nat. Hist., Vol. VII, 1861, pp. 389-391.
Primordial. Crosby and Barton: Am. Jour..Soi., 3d series, Vol. XX, 1880, pp. 416-420.
Upper Cambrian. C. D. Walcott: Am. .Jour. Sci., 4tli series, Vol. VI, 1898, pp. 327-328.
In 1861 it was pointed out that the coarse conglomerates of the southern
poi-tion of the Carboniferous field contained quartzite pebbles carrying two
species of Lingula (L. prima and L. antiqua) referable to the Potsdam sand-
stone. In 1880 Crosby and Barton announced the occurrence of Scolithus
linearis in the same conglomerate pebbles near Newport, Rhode Island.
During the present survey the writer has Yound these fossiliferous
pebbles farther north and east than the localities described by earlier
investigators. Other occurrences are noted in Dr. Foerste's section of this
110
GEOLOGY OF THE jS^ARRAGANSETT BASIN.
monogTiiph. Lingulse (now Obolus, see p. 113) were found in a pebble in the
red Carboniferous conglomerate on the east bank of Abbots Run, between
Lanesville and Arnolds Mills, Rhode Island. Eastward an Obolus pebble
was found on the beach near Marshfield, Massachusetts, together with a
large fragment of quartzite carrying the long, parallel, closely set burrows
of Scolithus linearis. Botli of these frao-ments weva within the Dossible ransre
Fig. 5. — sketch map of distribution of upper Cambrian pebbles. The uorth-south lines represent the supposed direction
of glacial motion during the maximum development of the jS'ew England glacier.
of glacial streaiu drift from the northeasternmost outcrops of Carboniferous
conglomerate in the main basin.
In July, 1895, I found a small sand-blasted Obolus pebble on the cliff
near Highland Light in Truro, at the northern extremity of Cape Cod; and
another pebble, carrying the same brachio^Dod, was found in an ancient
beach on the ocean side of Provincetown. These pebbles are so far to the
east of the known Carboniferous conglomerates on the mainland that their
dei'ivation from the main basin or from the Norfolk Basin seems improbable,
particularly for the reason that the movements of the glacial currents and
UPPER CAMBRIAN PEBBLES. Ill
the drainage from the ice which were concerned in the distribution of the
pebbles seem to demand, in our present knowledge, an origin from some
point in Massachusetts Bay, as will be seen from an examination of the
accompanying outline map (fig. 5) of the lines of glacial flow in eastern
Massachusetts during the time of formation of the Cape Cod moraine. It
is true that in the closing stages of ice retreat there are indications about
Boston of a more easterly set in the ice, as if it were controlled by the local
slope to the sea. If this movement extended as far south as the Duxbury
shore, the derivation of the pebbles from the northernmost areas of con-
glomerate may be accounted for; but these fossiliferous pebbles have not
been found as yet in the Norfolk and Boston areas, either in the con-
glomerates or in the glacial drift, though quartzite pebbles abound. Glacial
striae on a granitic ledge in Marshfield gave a reading of several degrees
west of north, but this locality is in the region of the Pljaiiouth inter-
lobate moraine, and does not indicate that the ice moved beyond this line
of accumulation in this direction to the eastern shore of Cape Cod Baj^.
The Obolus pebbles are very abimdant in the beaches of the south
coast, as far east as Nantucket and as far west as Block Island, being
most common in the intermediate area on Marthas Vineyard. The pebbles
have been dispersed southward by the glaciation of the Carboniferous
ledges of the mainland.
The earlier reference of these fossiliferous quartzites to the epoch of
the Potsdam sandstone has recently been confirmed by Walcott,^ who states
that the brachiopods have their closest affinity in the upper Cambrian
fauna of the Newfoundland area. As yet the beds have not been found
in situ, an > little else is positively known regarding the upper Cambrian
formation of this portion of New England than that which may be inferred
from a collection of these pebbles. The information thus obtained may be
briefly stated as follows.
Neglecting the question of superposition and the alternation of similar
beds with like faunas, data for which matters are of course wanting in the
pebbles, the upper Cambrian of the area whence the pebbles came appears
to have been composed of at least these three biological divisions:
1. An Obolus sone of light- colored quartzites. — The pebbles of this zone exhibit
bands, 3 or 4 inches thick, of these gregarious shells, usually preserved as black gra-
' Letter to Professor Shaler.
112 GEOLOGY OF THE NARRAGANSETT BASIN.
phitic crusts, and less commouly as white calcareous shells. The shell ; occur mostly
as detached valves, with their concave or interior faces turned downward upon the
bedding planes, evidently as the result of current action strong enough to invert the
shells when their saucer-shaped edges were opposed to the bottom drift, but not
powerful enough to move them when their smooth oval backs were presented to the
moving water. The existence of currents and shallow-water conditions is further
attested by examples of pebbles with marked ci'oss bedding, the "top-set" layers of
which, with contained shells, confirm the explanation here given for the position of
detached brachiopod valves.
The variations in the quartzitea and the irregularities in the fossiliferous layers
suggest that this zone alternated with bands of barren quartzite, described as ISTo. 3.
2. A Scolithus linearis zone of lif/ht-colored quartzites. — Pebbles carrying Scolithus
are by no means so common as the Obolus pebbles; they are most abundant in the
beaches of Marthas Vineyard. A cobble found on the beach of Marshfield Keck was
lOi- inches long, 6 inches thick, and 6 inches across, the burrows being C inches long
and worn off at both ends. Walcott notes their absence from the materials which he
studied.
3. A barren zone or zones of quartzites of various colors. — Some of the quartzite
pebbles included under this head may be of other than upper Cambrian age. since
quartzites of different periods occur along the western margin of the basin.
A few quartzite pebbles traversed with quartz veins older than the
Carboniferous sediments have been observed, from which it is to be inferred
that the iipper Cambrian formation underwent some deformation attended
by the segregation of silica in veins while the beds were still deeply
buried, but under what depth of cover is not exactly known. The presence
of Silurian fossils in the Miocene gravels of Marthas Vineyard maj^ indicate
the continuance of deposition in tlais field during the succeeding Silurian
period.
Until fossils are found in the quartzites which are known to occur in
the outlying region, the exact source of the pebbles in the Carboniferous
conglomerates must remain in doubt. It should be noted that the erosion
of pre-Carboniferous quartzites has fm-nished at least three-fourths of the
coarse fragmental material in the Carboniferous grits and conglomerates.
The area of erosion of so much coarse material, ranging to pebbles a foot
or more in diameter, as must have been the case with the now elongated
quartzite pebbles of the conglomerate at Newport, could not have been far
distant.
While the preponderance of large quartzite pebbles and fossiliferous
examples in the southern portion of the Carboniferous field favors the
UPPER CAMBRIAN PEBBLES. 113
idea that the derivation was from the south and east, the evidence is
good only for the pebbles in that part of the area. The quartz pebbles on
the north and west may equally well have been derived from those
directions for all that is known regarding the neighboring areas, particu-
larly since the texture of the Carboniferous deposits is mainly consonant
with the hypothesis of a peripheral origin of the sediments contained
within the present limits of the basin.
In conclusion, it need only be said that there appears to have been
nearly continuous deposition in this field throughout the Cambrian period,
for though the middle Cambrian has not been identified south of Braintree,
it lies within the same geological province. The change from the mud of
middle Cambrian times to sandy bottoms of upper Cambrian times in this
portion of New England apparently indicates progressive shoaling and
uplift of the sea floor.
Since the above account was written, Walcott^ has published a careful
revision of the fauna of these fossiliferous pebbles, referring the forms to
Obolus (Lingulobulus) affinis Billings and 0. (i.) spissus Billings, and to a
new species Ohohis (Lingulella) rogersi. Walcott suggests the derivation of
the fragments from an area of erosion lying in the vicinity of Newfoundland.
SILUKIAN PERIOD.
There are no known clastic rocks of Silurian age in situ in this basin.
Certain terranes in the southern and western parts of the area formerly
referred to this period are now regarded as either Cambrian or Carboniferous.
CHBBT PEBBLES.
The possible former existence of a Silurian formation in this portion
of the coast is indicated by the occurrence of chert pebbles carrying
upper Silurian corals in the Miocene gravels^ — the "osseous conglomerate"
of Hitchcock — at Gay Head and elsewhere on Marthas Vineyard. I am
indebted to Mr. C. D. Walcott for the determination of the age of these
chert pebbles.^ Their origin is involved in the same mystery which sur-
rounds the upper Cambrian pebbles.
' Note on tlie braoMopod fauna of the quartzitic pebbles of the Carboniferous conglomerates of
the Narraganaett Basin, Rhode Island, by C. D. Walcott: Am. Jour. Sci., 4th series, Vol. VI, 1898, pp.
327-328.
- In an early notice of them, based on scanty material, I mistook the single coral then found for
a Cambrian form. Am. Geologist, Vol. IX, 1892, pp. 243-247.
MON XXXIII 8
CHAPTER III.
THE IGNEOUS ROCKS OF THE BORDER OF THE BASIN.
GRANITIC ROCKS.
The granitic rocks which border this basin from Wrentham eastward
and thence along the margin in Plymouth County southward and westward
to Fall River are designated Archean on the most recent maps. The rocks
are mainly hornblendic granitites.^ The opinions which have been published
regarding the origin and time of eruption of these rocks are various and
often contradictory. Edward Hitchcock, if he can be said to have held a
definite opinion upon the subject, was inclined to represent the granitic
masses as erupted after the Carboniferous formations were deposited. In
1882 Wadsworth clearly showed that the hornblendic granitites in Braintree
are erupted through slates now known to be of middle Cambrian age. The
granitite of that locality is then more recent than the middle Cambrian.
Except for a few detached areas, all around the border of this part of the
basin the granitite extends beneath the Carbonifei'ous basal beds, which are
in large part made up of the little-worn waste from the granitite. At no
point in the northern half of the field has true granite been found in
eruptive contact with Carboniferous sediments.
The coarsely crystalline texture of the granitite along most of the
margin indicates, according to the accepted opinion, that the rock which is
now exposed at surface crystallized at a depth and under a cover of some
thickness, ^^robably in part of sedimentary rocks removed from this portion
of the area before Carboniferous deposition set in. Some of the Cambrian
formations undoubtedly formed part of this cover. No small depth of the
granitite must likewise have been canned away. At Braintree the zone of
granitite with a finer texture, due to the more rapid cooling near contact
with the slates, is preserved, and gives a minimum thickness of several
scores of feet between the contact and the inner coarsely crystalline rock.
Although the several varieties of granitic rocks in the area named are
' The " syenite " of Edward Hitchcock and earlier writers.
GRANITIC EOCKS. 115
essentially coterminous, these variations ai-e of sufficient extent to be indicated
when the mapping of their areas is undertaken. All about the northern mar-
gin, j^articularly near the Norfolk County Basin, where the red Carbonifer-
ous sediments abound, the feldspar of the granitite is in many localities of a
deep-red color. The association of these red feldspars with the red Carbonif-
erous rocks along this northern border of the field maybe without significance,
but the relation is noteworthy. The coloration of the feldspar, however,
has arisen apparently through the penetration of an iron oxide in solution,
following upon atmospheric decay. The oxidation of the iron-bearing sili-
cates in the granitite, e. g., the biotite and the hornblende, may have fur-
nished the iron, in which case there is no reason for supposing that the
coloring matter has leached downward from the formerly overlying red
Carboniferous beds. On the contrary, it is more probable tliat the red beds
owe their color to this iron oxide ha\ang- been set free in pre-Carboniferous
times. The surface exposures of this red granitite are simply the underlying
base of the zone of decayed rock which was swept off in the making of
the Carboniferous sediments. The objection which may be raised to this
view is that the granitite has been at least twice exposed to atmospheric
decay, once in pre-Carboniferous times, and again in recent geological
times, and that the red color of the feldspars to-day may be due to recent
rather than to ancient decay. But the arkose at the base of the Carbonif-
erous is sufficient proof of the ancient period of atmospheric decay, and
the immediately overlying red beds show that the process of rock discolor-
ation by percolating iron oxides went on in early Carboniferous time
essentially in the manner advocated by Russell.
The possibility of the coloration of sediments, at least locally, by this
means is attested by observations Avhich were made during the present
survey. At one point in the region of red granitite I was struck Avith
the redness of the water standing in the bottom of a small test quarr}^,
and with the film of red mud deposited CA^erywhere beneath the Avater
level. There can be no doubt, therefore, that the red g-ranitites are at
the present time capable of staining sediments Avith a red iron oxide film.
This process seems to be a local instance contrary to the general A^ellowish
and brownish hues so Avidely noted as the result of decomposition of rocks
in this latitude.^
' W. O. Crosby, Am. Geologist, Vol. VIII, 1891, pp. 72-82.
116 GEOLOGY OF THE NAERAGANSETT BASIN.
Near Easton the glacial drift from the granitite area carries a variety
of the rock of bluish-white color with large crystals of hornblende and
prismatic crystals of fegirine. At a few points the rock becomes fine
grained and is in contact with undetermined rocks, presumably pre-
Carboniferous elastics. Such contacts may be observed north of Mansfield
and near Hanover Four Corners. In Montello, north of Brockton, the gran-
itite with a pink feldspar was seen to contain small veins of prehnite.
Along the eastern border of the basin, in Plympton, there also is a fine-
grained granitite. Southward, in the northern part of the area represented
on the Fall River sheet, red granitite is again seen in bowlders, and the
ordinary phase of the hornblendic granitite is well exposed in the quarries
at Fall River, though here the rock has been locally sheared and in zones
is quite gneissoid.
In conclusion, it can not be said that the facts at hand warrant a more
definite statement than that these granitites were erupted at some period
betAveen the Carboniferous and the middle Cambrian. The granitic rocks
near Providence appear, as shown on page 105, to be older.
PLYMPTON FELSITES.
In Plympton and extending toward Halifax is a small area of reddish
and greenish felsites, the exact limits of which are not known. At one
point on the eastern border of the Carboniferous area the felsite in the form
of a dike several feet wide may be seen cutting the granitite. North of
this locality is the main occurrence, in the form of a flow, the bands of
which dip gently westward toward the Carboniferous basin. As no Carbon-
iferous strata are seen in connection with the igneous rocks at this point,
their age is not definitely known. The imperfect exposures seem at least
to indicate that the felsite broke through the granitite, and the absence of
Carboniferous rocks at the locality, taken in connection with the fact that
the supposed boundary of the basin passes through this locality, may be
interpreted to mean that the felsite flowed out upon the surface of the
granitite at the beginning of Carboniferous deposition. This conclusion
is supported by facts set forth on page 155 concerning the felsites of North
Attleboro.
ACID IGNEOUS liOOKS. 117
GRANITE-PORPHYRY.
Granite-porphyry occurs in the northwestern margin, about Diamond
Hill and half a mile northwest of Arnolds Mills.
This latter area affords a tolerably fresh rock, characterized by the
presence of large grains of quartz and orthoclase, with microscopic garnet
as a rare accompaniment. The quartz occurs in rounded and angular
grains. The angulation of the quartz is probably in part due to a move-
ment of the magma after partial cooling. The quartz also shows embay-
meuts of the groundmass. It is further characterized by the usually
observed fluid inclusions, with gas bubbles, which move about in the cavi-
ties. Some of these bubbles simply change their position with reference
to gravity when the slide is turned up or down; others keep up a contin-
ual oscillatoiy movement, which is independent of the accidental jarrings
due to the manipulation of the stage of the microscope. Magnetite or
ilmenite is present. Apparently the iron ores of the granite-porphyries of
this district tend to form aggregates having the external grouping of den-
dritic minerals. Chlorite is present in the groundmass, as are also small
crystals of hornblende. Garnet occurs in isotrojDic sections with a trian-
gular outline, a pinkish tinge in plain light, and witli traces of cleavages.
Concerning the interpretation of these porphyry stocks, see page 155.
OTHER ROCKS.
Farther south are bosses of hornblende rock which break through the
Blackstone series This is a fine-grained, dark-blue rock, evidently of
igneous origin. Under the microscope it shows considerable alteration.
Hornblende occurs in idiomorphic crystals, affording basal sections. There
is a great deal of what appears to be secondary hornblende, shown by
its lack of crystalline outline. Chlorite is abundantly present in scaly,
felty aggregates. Muscovite exists, probably as an alteration product of
one of the original feldspars. Calcite occurs in the rock, and is probably
derived from a lime-soda feldspar. The idiomorphic character of the horn-
blende crystals, where this character is preserved, the nature of the second-
ary products, and the fact that quartz is present, probably as a secondary
product, lead to the opinion that this rock was originally a diorite charac-
terized by little or no free quartz, the quartz now visible having been
derived by the breaking up of the bisilicates.
118 GEOLOGY OF THE IS^ARRAGANSETT BASIN.
Diamond Hill is a mass of quartz veins probably segregated as late as
the period of the Wamsutta formation of the northern border. The quartz,
as shown by Dr. Foerste's studies, is mainly developed in the southern part
of a mass of granite-porphyry having a superficial extension of about 2
square miles.
GABBRO HILLS OF SHARON.
An elongated lenticular area of gabbro with diorite occurs in the
Wrentham-Hingham granitic uplift, bordering the southern side of the Nor-
folk County Basin. The following notes are from a description of tlie rock
hj Messrs. J. R. Finlay and H. I. Richmond, jr., to Avhom I am indebted for
the use of their manuscript report:
From North Foxboro to Gantou Juiictiou there is a heretofore undescribecl range
of hills composed almost entirely of gabbro. The area of this rock is 7 miles long and
its greatest breadth about 2 miles. The highest point of this range is Moose Hill,
which attains an elevation of 5G0 feet. Southwest of Foxboro the gabbro extends in
disconnected bosses as far as Wrentham.
At Foxboro, Mansfield, East Foxboro, and Canton there are large ledges of
coarse, light-colored, hornblendic granitite, so situated as practically to surround the
gabbro on at least three sides. In the gabbro and along the northern side are frequent
dikes of aplite. The outcrops of a finegrained granitite along the northern side attain
considerable size. Exactly what is the relation of this finegrained granitite to the
coarser granitite which covers so much territory to the southeast can not be determined
in the field, as they are nowhere in contact.
The coarse-grained granitite is found in several iilaces, as, for instance, just west
of Canton Junction, penetrating in an intricate manner patches of crystalline schist.
.In the railroad cut just north of the station at Canton Junction there is a large
exposure of coarse-grained hornblendic granitite, while south of the station and just
east of the gabbro is a large area of biotite-granitite. Adjoining these rocks to the
south and east is the light-colored coarse granitite of the region. South of Canton
Junction, a mile east of the railroad, there is a large boss of diorite which has burst
through the granitite. Blocks of coarse-grained granitite are inclosed in the diorite.
Between the diorite and the gabbro is a strip of granitite a quarter of a mile wide.
The coarse granitites aie older thau the diorite, but are younger than the schists
at Canton Junction. The gabbro is older thau the fine-grained granitite dikes pene-
trating its mass, but their relation to the coarse granitites is unknown. The youngest
rock of the region is a diabase, which is found in dikes cutting the other rocks.
A petrographical study of the gabbro showed variations to a dioritic phase. The
diorite exists in certain areas in the gabbro.
CHAPTER IV.
THE CARBONIFEROUS BASIN.
The rocks referred to the Carboniferous period in the Narragansett
Basin are grouped together, either for the reason that they are known to
contain the fossils pecuHar to this period or because they are stratigraph-
ically united with those which are thus fossiliferous. The members of the
formation are arkoses, conglomerates, sandstones, shales, and coals, with a
great variety of secondary structures. The strata are almost everywhere
bent into steep-sided folds. Limestones and rocks of igneous origin are
conspicuous only in certain parts of the area. The beds are nonmarine,
and present no signs of equivalency in their lower strata with the lower
Carboniferous or Mississippian series.
In a geiaeral way the strata of the basin exist under two phases: One
is a belt of much metamorphism, beginning near Pawtucket and extending
southward and widening to the sea in Narragansett Bay, but most pronounced
along the western boundary (see fig. 6, p. 120). The second phase is char-
acteristic of the greater portion of the remainder of the area, or about two-
thirds of the whole, extending eastward and north into the Norfolk County
Basin. In this field the effects of metamorphism are rarely so great as
seem commonly to be believed by geologists. The transition between the
two fields is often very abrupt. The geologist who should pass from the
nearly vertical metamorphic strata of the East Side in the city of Provi-
dence, Rhode Island, to the slightly folded and unaltered sandstone and
shale beds of East Providence, would, from a comparison of the rocks
alone, be led to infer that there was in this field a set of very ancient tilted
rocks flanked on the east by strata of much less antiquity. So short is the
space between the two rock phases at this point, being the width of the
Seekonk River only, that one is led to believe that an intermediate zone
of considerable width has been concealed by a fault.
In the less metamorphosed area, with which this part of the report has
120
GEOLOGY OF THE NAEEAGANSETT BASIK
mainly to do, the acquisition of secondary characters in the strata is very
closel}^ related to the degree of tilting which they have undergone. Aside
from one or two narrow belts of dynamic metamorphism, accompanied by
the development of new minerals, the alteration is generally limited to the
production of cleavages and joint structures. It is on account of this lesser
degree of alteration and the identifiable condition of plant remains that
Fig. 6, — Map showing distiibution of metamorphosed Carboniferous rocks.
A, Narragansett Bay area of maximum metamorpliism ; B, Winueconnet area ;
C, Morrill's area in Norfolk County Basin.
this portion of the field affords the best ground in the Carboniferous basin
for determining the succession.
In the subsequent pages the attempt to establish certain rock g-roups
in a typical area will be followed by a description of the extension of the
rocks over the remaining field. Before describing the rocks, however, I
shall discuss the facts relating to the general structure and the boundary of
the basin.
THE CARBONIFBEOUS BASIN,
121
GENERAL STRUCTURE OF THE BASIN.
The broader secondary features of the basin — the system of folds with
their axes and the parallel direction of the borders — are relatively simple.
The structural outline of the basin is that of a ship's knee, with the
ang'le on the northwest, one arm extending southward to the mouth of
Narragansett Bay, the
other eastward toward
Cape Cod Bay, and the
inner curve forming the
border from Tiverton
northeastward to Lake-
ville. If a line be drawn
from the northwestern
corner near Diamond
Hill (see fig. 7) south-
eastward to a bisection
of the curvilinear border
near Fall River, it will
pass through the three
deep synclinal depres-
sions in which the upper-
most conglomerates of
the Carboniferous have
been infolded and 23re-
served from denudation.
On the northwest this
line also passes through
the small area of pro-
found dislocation and FicT.—lIap showing general outline of the Narragansett Basin. A-B, line pass-
ing througli deeper synclines of middle of the area; aa, inlier of granitite and
uplift which brings the Cambrian at HopplnHUl and the Diamond HiII quartz mass on western border^
, . bb, granitic and gnelssie inliers near Bristol, Rhode Island; CO, synclines with
granitite Ol Xi O p p l n coarse conglomerates ; oo, synclines along northern border of the basin ; dd,
.^-j.,-,, 1 /-. 1 . -I gneiss structure in New Bedford area-
Hill, the Cambrian, and
the lower Carboniferous strata to the surface. West of this line the strikes
trend nearly north and south; east of the line they trend about east and
west. This axis of pressure, moreover, appears to have been that in
122
GEOLOGY OF THE NAERAGANSETT BASIN.
-;-- i
■hk
/ s,/
which powerful thrusts have acted on the region
to the southeastward. The granitite of the south-
ern border in the region of this axis, notably
about Fall River, is sheared and rendered locally
schistose by reason of the pressure to which it has
been subjected.
If we continue this line .still farther southeast-
ward, it will be observed that the gneisses of the
5 New Bedford area exhibit structures roughly con-
ii centric to the Carboniferous strikes on the north-
I west (see dd, fig. 7). The whole array of structures
» points to an older land mass, now submerged, which
I lies in this southeastern versant of the New England
0 coast. From this area the deposits of later times,
1 wrapped about its northern and western sides,
1. appear to have been pressed toward the northwest.
g The southern arm of the basin is parallel in
structure with the strikes of southern New England
I westward to the Taconic range. The eastern arm
I of the basin coincides in trend with the Norfolk
s County and Boston basins in their eastern parts.
g These last-named show also, in their inner western
I extensions, the tendenc}^ to become concentric with
g reference to a point on the southeast.
g The number of great folds in the basin is few
I (see figs. 8 and 9). Along the line above referred to
» there are probably not more than four great syn-
£ clines and three intervening anticlines. None of
these folds appear on earlier sections of this basin
(see fig. 10). The great mass of sediments is here
thrown into folds having dimensions quite equal to
those of the Appalachian folds in Pennsylvania (see
fig. 8). From axis to axis of the same kind is a dis-
tance upward of 6 miles (see map, fig. 7). With
dips often of 45° or more, folds of so great a breadth
are commensurable only with a great thickness of
STEDCTURE OF THE BASIN.
123
strata, of which there can not be less than 12,000 feet now remaming.
East of this Hne the upper strata are apparently denuded and the structure
Fig. 9.— Outline map and general cross section of the basin.
is less well shown (see fig. 8), lai-gely owing to the covering of glacial
drift. In the southern arm, as is shown in Dr. Foerste's report, like
changes have taken place, and the incursion of the sea has done that which
is performed by sheets of sand and gravel in other parts of the basin.
124 GEOLOGY OF THE NAERAGANSETT BASIN.
MAPS OF THE BOUNDARY OF THE BASIN.
The progress in knowledge of the geology of this district is very Avell
represented by the delineation of the boundaries of the Carboniferous
formation on maps since the time of Maclure. In his map of 1817 this
field of rocks, then called "Transition," is represented as a triangular area,
with the base on the eastern shore of Narragansett Bay, between Providence
and Westport Harbor, and the apex at Boston.
The first official surveys, those of Hitchcock in Massachusetts and
Jackson in Rhode Island, the final maps of which were published in 1841
and 1840, respectively, gave the boundaries as they have been commonly
represented on compiled maps up to the present time. Dr. C. T. Jackson's
map of 1840 represents the boundary in Rhode Island with much accu-
racy, but a strip of the more highly metamorphosed beds, in Cumberland
on the north and in Kingston, South Kingston, and the southern part
of Jamestown on the south, is included in his group of "primary rocks,"
as are also the basal members of the Carboniferous along the Fall River
shore.
Edward Hitchcock's map of 1841 gives the outlying boundary of the
Carboniferous with much fidelity, but the shoulder angles, probably due to
cross faults, along the northern border are not shown. Owing to his belief
in the Devonian age of the red strata in the northwestern part of the field,
an attempt was made to draw a line between these beds and the Coal
Measures. No attempt is made to show the inliers of granitic and other
rocks in North Attleboro and Namasket; indeed, they are nowhere described
by him.
A later map, entitled Bristol and Rhode Island Coal Field, published
in 1853,^ represents Devonian rocks as lying in a belt along the western
border of the basin from Cranston northward into the Norfolk County Basin,
and as sending out branches near Burnt Swamp Corner eastward along the
northern border of the main basin to Foxboro and westward toward Belling-
ham. The occurrence of the Carboniferous formation along the Fall River
shore is not 5^et recognized, nor are the outcrops of granite at Namasket
and North Attleboro. The same is true of the horseshoe fold of the red
rocks which occur in North Attleboro.
' Massachusetts House Document No. 39, March, 1853.
BOUNDARY OP THE BASIK 125
Sir Charles Ly ell's map of 1845 is fairly accurate as regards the
boundaries of the basin, but the southern half of the Massachusetts
extension of the Carboniferous is erroneously colored to represent the Old
Red sandstone, or Devonian. The connection with tlie Norfolk County
Basin is not shown.^
Sir W. E. Logan, in the geological map of Canada, dated 1864,
accompanying the Atlas of 1865, represents, on the authority of James
Hall, the ou.tlines of the Carboniferous basin and its connection with the
Norfolk County Basin, the beds of which latter field are for the first time
colored as Carboniferous.
C. H. Hitchcock published a map in 1871 in which a barrier of
granitic rocks between the red beds of the Narragansett Basin and the
Norfolk Basin is again erroneously introduced. Other changes in the west-
ern boundary are made by i-eferring- a belt of strata to the Silurian.
W. O. Crosby's map of 1877 gives a generalized boundary of the
northern part of the basin, and an attempt is made to show the connection
between the NaiTagansett and Norfolk County basins. The Carboniferous
is shown extending as a tongue northward to Norwood in the Norfolk
County Basin, the underlying beds being, on the authority of Edward
Hitchcock, represented as Devonian.
In 1880 Crosby and Barton published an account of their tracing the
beds of the Norfolk County Basin into the Nairagansett Basin, and stated
their reasons for considering all the beds to be Carboniferous, but they did
not publish a map.
The latest, compiled general geological maps of the United States^
perpetuate the error in regard to the nature of the connection between the
Norfolk and Narragansett basins, a bond which was correctly shown on
Logan and Hall's map of 1864, and still earlier under the coloring of
Devonian in the Hitchcock map of 1841.
BOUNDARY OF THE BASIN ON THE KOETH AND EAST.
From Cranston to the Blackstone River. In tho SOUtllWeSt COmCr of tllO PrOvidcUCe
quadrangle the basal beds of the Carboniferous are seen standing in nearly
vertical attitude against the boundary wall of the pre-Carboniferous series.
■ Travels in North America, Vol. II, New York, 1845, PI. II.
=^C. R. Van Hise, after McGee and Hitchcock: Bull. U. S. Geol. Survey No. 86, PI. XI. W. J.
McGee: Fifth Ann. Kept. U. S. Geol. Survey, 1884, PI. II.
126 GEOLOGY OF THE IS^AERAGANSETT BASIN.
The angular fragments of the pre-Carboniferous rocks contained in these
beds, together with the meridional strikes of the Carboniferous as con-
trasted with the nearly east-west strikes of the older clastic series, afford
abundant evidence of the unconformity. The exact contact is not shown.
North of this locality the Carboniferous beds do not appear clinging to the
escarpment above the level of the glacial sand plains. In succession along
this escarpment, granite, gneiss, schists, and quartzite come up to the plane
of the base of the Carbonifei-ous, indicating the varied lithological character
and structure of the floor on which the sediments were laid down along
this western border. Direct evidence of faulting is wanting. For most of
the distance the lowest and nearest visible outcrops of the Carboniferous
are from 2,000 to 3,000 feet eastward of the line, and probably at approxi-
mately that distance above the base of the series. Throughout this section
a distinct valley exists along the contact; its western wall is formed by the
escarpment of pre-Carboniferous rocks, including some Carboniferous beds
lying to the west and forming a part of the escarpment at the point of
beginning;^ its eastern wall is formed by a broken ridge of hard sandstones
which stand up to the level of the adjacent peneplain developed on the
crystalline area to the westward. This ridge is broken through at Cranston
and Olneyville; and in each case the gap is opposite a valley opening
eastward out of the crystalline area. The deep reentrants in the pre-
Carboniferous rocks are thus shown to be of a date later than the Carbon-
iferous period and in no waj affect the boundary line by their having
been originally filled with sediments. On the assumption that the peneplain
is of Jura-Cretaceous age, the denudation of the Carboniferous soft rocks
below that level is an index of Eocene and later erosion, and these valleys
along and across the contact are post-Cretaceous. The cross valleys are
not of glacial origin; the movement of the ice was nearly at right angles
to their course. The same remarks concerning the age of topographic
features apply to the valley of the Blackstone, the course of which is else-
where described in this report. It suffices to state here that it turns from
a southeast to a south course immediately on entering the basin.
'Ill tracing the boundaries of the rocks lying on the western boundary of the Narragansett
Basin, Mr. J. H. Perry, of the United States Geological Survey, has recently shown that metamorphic
Carboniferous aikoses ami conglomerates occupy a small area, about half a mile wide, lying to the
west of the boundary as drawn by Dr. Foerste and myself where our maps join.
BOUNDARY OF THE BASIN. 127
From the Blackstone River to Sheldonville. TlirOUgllOUt tllls nOrtliem half of tllB
western boundaiy actual contacts of the Carboniferous upon the underlying
rocks have not been seen. North of the Blackstone RiA'^er the NW.-SE.
strikes of the Blackstone series can be traced to within short distances of
the NE.-SW. strikes of the Carboniferous beds, indicating from the angle
which the latter make with the western boundary that they have probably
been faulted. From Millers River northward a boundary valley continues
as far as Diamond Hill. In the Millers River section gray basal conglomer-
ates dip off eastward at steep angles, but the valley is wholl}' excavated
in the Carboniferous rocks. Northward, in the Thompsons Hill area, the
Coal Measures come in, apparently by downfaulting along the border.
From Diamond Hill to Joes Rock, seen on the Franklin atlas sheet, the
Carboniferous rocks are in unconformable relation with the lower Cam-
brian red shales, but details of this relation are wanting.
Connection between the Narragansett and Norfolk County basins. At SheldoUvillc tlie rOck
of the Narragansett Basin can be traced, as stated by Crosby and Barton
in 1880, into the southwestern end of the Norfolk County Basin, through
a pass not exceeding 2,500 feet in width between walls of the hornblende-
granitite. The hornblende-granitite comes up to this stratigraphic isthmus
with nearl}^ rectangular corners, as shown in the map, fig. 7 (p. 121).^
Sheldonville cross fault. — Tlie most reasouablc explanation of the rectangular
boundaries of the Carboniferous and granitic rocks at this point is, as sug-
gested by Mr. J. R. Firday, the occurrence of a fault passing in a NNW.-
SSE. direction. This view is confirmed by the extensive faulting of the
Carboniferous beds southward through Plainville in the same direction, as
Mr. Finlay has amply demonstrated in the field.
Actual fault contacts in the Sheldonville pass have not been seen.
There is an outcrop of red sandstone striking NE. and dipping 60° N. in
the pass in the western granitic corner, very close to the supposed fracture.
From Sheldonville to Foolish Hill.— From ucaT Bumt Swiiuip Coruer eastward the
boundary can be fixed with approximate exactness. Messrs. L. S. Griswold
and C. F. Marbut have determined the relations of the rocks at a number
' Some of the earlier geologists supposed that the Ehode Island and Worcester areas are con-
nected through the Blackstone Valley, but Prof. Edward Hitchcock showed that these areas are
separated by a wide district of gneiss. Dana, Manual of Geology, 3d ed., 1880, p. 319. Hitchcock,
Final Report on Geology of Massachusetts, 1841.
128 GEOLOGY OF THE NAREAGANSETT BASIN.
of points as far east as Brockton. The basal series of the Carboniferous
may be seen within a few feet of contact with the g-ranitite in Wrentham,
in the low hill half a mile north of the Shepardville reservoir. So far as
can be observed, the strata are simply downfolded without faulting. Along
this line there is little topographic expression to the contact. The Carbon-
iferous area is covered by a low, gently undulating drift plain, while the
granitic rocks rise into rounded knobs having elevations of from 100 to
200 feet above the plain on the south.
Foolish Hill fault. — Midway between Foxboro and Mansfield the boundary
line makes a rectangular turn along the western face of Foolish Hill.
This side of the hill presents a long, smooth wall, inclined steeply westward.
The basal beds of the Carboniferous rise up on the southern face of this
granitic hill, with steep dips to the southward, and reappear on the low
ground to the westward with an oflFset of 2,000 feet or more to the north.
The railroad from Mansfield to Foxboro follows approximately the line of
this fault.
From Foolish Hill to Brockton. — Eastward to Eastou tho coutact can be traced
with less certainty. The attitude of the basal Carboniferous beds on the
south varies as regards angle of dip from point to point, but is generally
much steeper as the contact is approached. This change of dip is so
marked in some cases as to suggest unconformity between the red basal
series and the overlying gray carbonaceous beds. While, as before noted,
no actual faulting can be shown in these cases, it may be questioned
whether the steeper dips along the border do not express the upward drag
of the edges of strata from downfaulting of the rocks in the basin.
Between Easton and Brockton there are positive indications of small
faults along the boundary, shown in actual exposures, but the precise nature
of the disturbances and their bearing upon the form of the basin in this
region are not clear on account of the drift coating.
A mile northeast of the last-named locality is a very considerable
irregularity in the boundary, by which, according to Messrs. Griswold and
Marbu^t, the red beds in vertical positions are let into the granitite floor.
Still nearer Brockton the sudden disappearance of red sandstone in the
drift for a space indicates a displacement or disappearance of the beds by
erosion. The fact is worth noting here that the coarse pink granite just
south of Montello railroad station is faulted along NE.-SW. planes.
BOUNDARY OF THE BASIN. 129
In the course of grading the bed of the Old Colony Railroad from
Brockton northward, since the field work for this report was finished, Car-
boniferous gray sandstones with fossil plant stems were exposed, according
to the studies of Mr. M. L. Fuller,^ for some distance north of the main
boundary line on either side of that city. I am indebted to Mr. Fuller for
information concerning the boundary as drawn on the accompanying map.
From Brockton to North River. — Outcrops of tlic Stratified rocks here become
very infrequent, but enough are exposed to define the approximate position
of the boundary.
shumatuscacant fault. — Betwceu Brocktou aud Abington there are angles in
the border which indicate the existence of cross faults, one in the path of
Beaver Brook, the other, and more unmistakable case, that along the line
of the Shumatuscacant River in Abington. By this latter dislocation the
boundary line on the east is set northward for the distance of a mile.
Through Rockland and thence eastward across Hanover to the north-
east corner of the basin, the boundary can be delineated only by drawing
a line south of the known exposures of granite and north of the first appear-
ance of Carboniferous rocks in the drift. The valley of Third Herring
Brook follows the boundary for a short distance, and the North River takes
an eastward turn across the line.
From North River to Lakeviue. — Aloug tliis llue the bouudary is, because of the
drift mantle, not accurately known. Granitite appears in Namasket about
4 miles west of the line, as heretofore represented on maps of the basin,
and it is not certain that this outcrop is a mere inlier. In the absence of
positive information on this point it is tentatively i-epresented as a part of
the eastern granitic area. Between North Plympton and Halifax the basin
is also made to include an area of felsites, the exact limits of which are'
unknown. The protrusions of the eastern margin into the basin in the form
of felsite in Plympton and of granitite in Middleboro are near enough to the
lines of anticlinal axes in this portion of the basin to lend support to the
hypothesis that the basement of the Carboniferous is exposed at these locali-
ties by the folding of that floor in conformation to the structure of the once
overlying strata. If this view be correct, we should expect to find the
lobate areas between the tongues of igneous rock forming synclines in the
'Anew occurrence of Cr-vboniferous fossils in the Narragansett Basin: Proc. Boston Soc. Nat.
Hist., Vol. XXVII, 1896, pp. 195-199.
MON XXXIII 9
130 GEOLOGY OF THE NAERAGANSETT BASIN.
Carboniferous. The single but pronounced meridional strike of the outcrop
near Judson post-office proves that the Great Meadow Hill syncline does
not extend to the eastern margin, and we are led, therefore, to infer that
other synclines exist in this heavily drift-covered region. The east-west
strikes of the Carboniferous in Hanover, where they are in close proximity
to the border running north and south, make it almost necessary to suppose
that there has been faulting along this line. Granite of a euritic texture
occurs south of Plympton, setting an eastern limit to the Carboniferous, and
there is thus no evidence to show that the Carboniferous extends toward
Cape Cod Bay east of the line drawn on the map.
In the Furnace Pond area reliance has been placed upon the distribu-
tion of the glacial drift, the incoming of granitic blocks in large quantities
being taken as the approximate northern position of the granitite on the
south of the basin. The line across the lakes, in Lakeville, is wholly
conjectural, but is confirmed by the position of granitite exposures three-
fourths of a mile southwest of Elders Pond.
From Lakeville to Steep Brook. — Froui tlic viciulty of Myricks soutliwestward
the contact begins to take on a topographic expression and is marked by an
ice-worn granitic escarpment, at the foot of Avhich runs the Assonet River.
Just south of Myricks the vallej^ of Swamp River breaks through the
granitite and is taken advantage of by the New Bedford branch of the Old
Colony Railroad. In Freetown the granitite is exposed in Washington
Mountain and near Break Neck Hill. Finally, at Steep Brook, seen on
the Fall River sheet, the basal arkoses and conglomerates are found resting
on the granitite and dipping off northwestward at an angle of 45°.
INLIERS.
In addition to the facts regarding tlie outlying boundary of the Car-
boniferous, a few statements may be made concerning the contact of the
formation with the inliers which have been noted in this jjortion of the
basin. Inliers are conspicuous features on Newport Neck, Conanicut Island,
and in the region about Bristol, for a description of which the reader is
referred to Dr. Foerste's section of this report.
There is only one definitely determined inlier in this northern part of
the basin — that of Hoppin Hill, in North Attleboro — though it is possible
that there are others, as at Namasket and in tlie Cambrian locality near
Diamond Hill.
BOUND AKY OF THE BASIN. 131
North Attieboro iniier. — 111 tlie Novtli AttleboFO inlier (see PI. XXIX, in Part
III), actual contacts of the Carboniferous with the subjacent Cambrian and
granitite are not exposed, but the evidence points to the unconformable
relation of th<j Carboniferous and Cambrian strata.
Namasket granitite area. — Horiiblende-granitite, similar to the rock of the
northern border of the basin, appears in a low outcrop about 60 feet above
the sea in the village of Naraasket, in the town of Middleboro. The expo-
sure by the roadside is upward of 200 feet in length, and is at a distance of
3^ miles from the nearest granitite outcrops to the southeastward. The
nearest visible stratified rocks are 2 miles south, and nothing is known
reo-arding the contact. It is not at all improbable, as above stated, that the
exposure of granitite at this point marks an anticlinal structure in the Car-
boniferous by which a tongue of the granitite protrudes into the basin from
the eastern border, as does the long, broad area from Hingham westward to
Sheldonville, separating the Narragansett from the Norfolk County Basin.
SUMMARY.
The boundary in this northern part of the field appears to be inainly
one of downfolded beds where the line extends east and west. Down-
faulting is suggested only where the line runs north and south. Corre-
lated with this evidence is the presence of arkose along the east-west
borders, and its almost complete absence along north-south lines in the
upper part of the basin. These faults are parts of a series which appear on
the east-west boundary lines as cross faults.
The type of fault crossing the boundary of the basin is repeated a
number of times along the northern border. These cross faults along the
northern margin do not clearly arise out of the physical conditions engen-
dered at the contact of two terranes so unequally acted upon by stress, but
rather they are regional dislocations arising in the pre-Carboniferous ter-
rane, their existence being clearly brought out by the rectangular notches
which they introduce into the boundary line. Outcrops are wanting to
show how far these faults affect the beds in the basin above the lowermost
strata. Even if the faults were limited to the granitite and the beds imme-
diately at the base, we should expect to find a local deflection of the strike,
in the form of a flexure, in the direction of the offset at some distance
beyond the margin of the fault plane.
1 32 GEOLOGY OP THE NAERAGANSETT BASIN.
It is to be noted that the faults along this border are of the normal
Basin Range type, the downthrow being in blocks on the east and west
of a relatively uplifted block in Easton. The northward recession of the
boundary east and west of this block is in accordance with this structure.
The system of faults is, moreover, transverse to the Wrentham-Hingham
uplift of igneous rocks. So far, however, these fractures have not been
traced into the Norfolk County Basin. The throw of these faults is not
necessarily great. The dip of the strata near Brockton and Abington is
generally low, not exceeding 15°, and the surface is level, so that a ver-
tical downthrow of 1,420 feet would account for the displacement of the
boundary 1 mile on a horizontal plane at the latter place.
The date of the faults is not in most instances determinable. They
are clearly post-Carboniferous, but their correlation with the dislocations
which deformed the Newark basins along the Atlantic coast in middle
Mesozoic times has not been proved.
CHAPTER y.
THE CARBONIFEROUS STRATA.
DETERMINATION OF HORIZONS WITHIN THE BASIN.
The earliest attempts to discriminate horizons within the limits of the
basin were made by Edward Hitchcock in the northwestern part of the
area, where, on lithological grounds, the red Carboniferous beds were
referred to the Devonian period.
Sir Charles Lyell, in 1845, mapped as Devonian a broad band of strata
extending through Rehoboth, Swansea, Taunton, and thence to the eastern
margin, but it is now known that the beds so mapped are Carboniferous-
In 1871, C. H. Hitchcock mapped a small area in the southwestern part of
Attleboro as belonging to the "Quebec group," and a strip along the west-
ern border of Rhode Island as Silurian, but both these occurrences are now
known to be Carboniferous. In the eai-lier work of T. Nelson Dale about
Newport, the Carboniferous and earlier strata were divided into Paleozoic
groups based on lithological characters. Beyond these incomplete maps no
attempts have ever been made to exhibit the formations which have been
recognized by several authors as forming horizons in the coal basin.
MEANS OP DETERMINING SUPERPOSITION.
The means of determining horizons in the Carboniferous rocks of the
Narragansett Basin are purely physical. As yet the fauna and flora of
the Carboniferous beds are too little known to be employed. A series of
basal arkoses overlain or replaced from point to point by simple quartzose
conglomerates can be traced fairly continuously about the margin, and may
be recognized at a few points in the interior. Above these is a great
succession of conglomerates, sandstones, and shales with coal seams, which
are rarely traceable for more than a few miles. The formation is preemi-
nently conglomeratic.
In the main, reliance has been placed on matching strata on opposite sides
of anticlinal and synclinal axes, checking these observations by gross meas-
urements of thickness and by observed gradations in texture and thickness of
individual beds. The results can be said to be little more than approxima-
tions. In portions of the area, particularly in the eastern part of the field, a
description of the geology can deal with little more than isolated outcrops.
134
GEOLOGY OP THE NARKAGANSETT BASIN.
I am of the opinion that, were the several horizons of shales explored
for fossils, a sufficiently differentiated flora would be found on which to
base a more satisfactory subdivision of the great middle series of sandstones
and shales than is here proposed on j^urely physical grounds.
Tabular vieto of the strata in the Narragansett Basin.
Northern field.
Southern field.
Group.
Remarks.
Local areas.
Characters.
Local areas.
Characters.
Dighton (Cd)
Rocky "Woods con ■
Coarse quartzile and
Purgatory
Coarse quartz-
Probably, though not
(1,000-1,500
glomerate.
granitic pebble con-
conglomer-
ite pebbles,
certainly, identical in
feet).
glomerates, with finer
ate.
usually
all parts of the field, ly-
Seekonk conglom-
conglomerates and
much elon-
ing in aynclines above
erate.
sandstone.
gated and
indented.
the Coal Meaaares.
Rhode Island
Westville shales
Alternations of fine
Aquidneck
Mainlyshales
Both the Aquidneck and
Coal Meas-
and Seekonk
and medium quartz,'
shales of
with coal
Kingstown series
ures (Cc)
sandstones.
quartzite, and gra-
Dr.Foerste.
beds.
of Dr. Foerete, when
(10,000 feet).
Tenmilo RiTer
nitic pebble conglom-
traced northward, ap-
beds.
erates, with pebbly
sandstones, sand-
stones (grauwacke),
pear to form equiva-
lent sections beneath
the Dighton group,
Mansfield beds.
shales, and coal beds,
Kings town
Mainly sand-
one on the eastern, the
Cranston beda,
becoming metamor-
series of
stones and
other on the western
Sockanasset
phic southward.
Dr.Poerate.
conglom e r ■
side of Narraffansett
sandstones,
Colors: Black, blue,
ates with
Bay, and both extend
Pawtucket
green, gray, locally
coal shales;
downward to the basal
shales.
red. Odontopteris
usually met-
beds in this typical
flora and insect beds.
aroorphic.
area.
"Wamsutta
[slates
Beds of quartz, quartz-
The Wamsutta beds are
(Cw) (1,000
Wamsuttai and
ite, felsites, felaite
not traceable south of
feet).
[shales.
breccias and felsite
Providence ; probably
Attleboro sand-
conglomerates, sand-
represented by lower
stone.
stones, arkose, and
strata of Dr. Foerste's
"Wamsutta c o n -
shales. Colors: Red,
Kingstown series. In
glomerates.
locally brown, and
green. Calamites.
the vicinity of Paw-
tucket the Coal Meas-
ures underlie the
Wamsutta.
Pondville (Cp)
Millers River con-
Quartz conglomerates .
Basa beds.
Quartzose
Essentially similar prod-
(100 feet).
glomerates, ar-
Coarse, white, gra-
conglomer-
ucts of decayed gra-
kose beds.
nitic waste or arkose.
ates and
arkose.
nitic land surface in all
parts of basin.
TTn com form ity.
"Widespread erosion interval, representing
Cambrian.
all of Silurian and Devonian
time and probably upper
Pre - Carbonif-
Broad exposures of granitite intruded into
Same as in northern field.
Pre-Carboniferous strata
erouB.
lower and middle Cambrian and pre-
not definitely deter-
Cambrian sediments.
i
mined; Cambrian or
pre -Cambrian.
BASAL BEDS. 135
foematio:n"s bei.ow the coal, measures.
pondville group,
basal aekose beds.
Along the northern border where observations can be made, the red
rocks of the Wamsutta series either rest directly on the granitite or are
separated from that basement rock by a sheet of grayish arkoses and quartz
pebble and quartzite conglomerates. It is evident that the first appearance
of red sediments was not simultaneous all along the border, but that it
de^aended upon local conditions, such as the debouchure of streams, the
230sition of headlands or bays controlling the nature of local shore-line
deposits. With the exception of the few places where the red sediments
designated as members of the Wamsutta series come in at the base, there
may be said to exist a horizon of sediments not of red color underlying the
Wamsutta and bearing in the nature of their particles, independently of
their position, every evidence of being a basal series. These rocks appear
not only beneath the red strata in the Narragansett Basin, but also in a
characteristic section in the western part of the Norfolk County Basin. I
shall refer to the exposures of these basement strata in the few localities
where they may be studied to advantage.
Foolish Hill exposures. — At the base of the Carboniferous, on the southern
face of Foolish Hill, between Mansfield and Foxboro, basal arkoses are well
exposed; but here thin bands of red slate begin to make their appearance,
a few feet above the base.
North Attieboro exposures. — In thc towii of Nortli Attleboro, on Division street,
and at points near the railroad station on High street, there are broad
exposures of a gray arkose derived from the disintegration of the horn-
blendic granitite. Similar exposures occur east of the town, where by
folding the basal series are brought up in close-pressed folds.
Pierces Pasture in Pondville, Norfolk County Basin. TllC clcareSt exhibition of the baSal
beds of the Carboniferous is to be found in the Norfolk County Basin near
Pondville Station, on the Walpole and Wrentham Railroad. The small
area known as "Pierces Pasture" exhibits in its topography much of the
ruggedness of an unglaciated region, insomuch that the nearly vertical beds
stand out in ridges where hard and resisting, or sink into depressions where
soft and yielding. The almost entire absence of glacial drift from the area
136 GEOLOGY OF THE NAREAGANSETT BASIN.
is due to its having been covered by a remnant of the ice sheet whose mar-
ginal sand plains surround the field on the east, south, and west. The
Carboniferous beds rest here. upon the grauitite and dip off steeply to the
north, in the form of a closed and puckered syncline plunging eastward,
the cross section of which structure is as follows, beginning on the sovith :
1. A small kuob of horublendic grauitite. This i)asses by almost inseusible grada-
tious into arkose.
2. Alternatiug beds of arkose and grits, with vein quartz pebbles, occasional
nodules of the grauitite, aud shaly partings.
3. Quartz-pebble conglomerate, with sandstone partings, the latter holding casts
and hollows of fossil trees from a few inches to more than a foot in diameter, often
closely pressed and forming a mere gash with an ocherous cellular layer. (The fossils
described by Crosby and Barton in 1880 were the casts of this locality.)
4. Eed and green slates, with sandy partings.
5. Fine quartz-pebble conglomerate in eastern part of the lot ; wanting in the
western section.
6. Eed and green slates, like 4 above, with flattened and cylindrical casts ; and
small greenish chloritic kernels, due to metamorphism.
7. Quartz-pebble conglomerate, with sandstone i^artings, containing casts and
molds of fossil trees; one cast 12 feet long and 12 by 18 inches in diameter.
Whole section 250 to 300 feet in thickness.
Northward the beds are concealed beneath a swamp. This section is,
on the whole, one of the most instructive basal sections in the Carbonifer-
ous field of Massachiisetts, and may be taken as typical for the general
history of the beginning of sedimentation in the main basin.
Absence of basal granitic conglomerates. It is a UOtOWOrthy faCt that whlle thc CntlrO
Carboniferous section, amounting probably to a thickness exceeding 12,000
feet, is mainly conglomeratic, there is in this northern half of the main
basin no widespread basal conglomerate such as we find exactly at the
base of many sections in the geological record. The general absence of
basal conglomerates and the presence of arkose along the border indicate
clearly the condition of the land surface from which the earliest sediments
were derived. The failure to produce pebbles of the original rock under
the first attack of denudation must evidently have been due to the deep
disintegration of the granitic terrane whence the sediments were derived
and the low grades of streams. By the disintegration of the feldspar and
the decay of the iron-bearing silicates of the igneous rock the crystalline
ingredients fell into the state of coarse sand, and in this form the superficial
portion of the granitite was removed to the area of deposition. It was only
BASAL BEDS. 137
later, as a result of renewed uplift of the land or of the deeper intrenchment
of streams and the incision of waves, that the fresh, undecomposed granitite
came into the grasp of the eroding agents, and, breaking up along planes of
fracture, made pebbles. In the meantime, there were portions of the granitic
terrane which did not disintegrate. These parts were the quartz veins and
nodular segregations of quartz in pegmatites, and to some extent, perhaps, in
dike rocks, which remained and formed pebbles. It is owing to this reason
that the first conglomerates overlying the arkose beds are composed mainly
of quartz pebbles. The considerable mass of these pebbles gives some idea
of the thickness of the decomposed granite section which was removed at
this time. In any section of the neighboring granitites at the present time
the volume of quartz large enough to form pebbles in a cubic yard of the
rock is relatively very small. Large and thick veins occur here and there,
but it is not conceivable that more than 1 per cent of the average granitite
mass would yield quartz pebbles. It is evident, tlaerefore, that a very
thick section of rock was subjected to disintegration and removal in order
to form a bed of quartz conglomerate 50 to 100 feet thick. How much of the
quartz came from veins in sedimentary formations into which the granitite
doubtless penetrated can not be known. The quartz would probably be
more abundant in these rocks than in the granitic stock itself. That the
depth of granite removed to form these ai'koses and quartz pebbles was
great is also indicated by the coarsely crystalline texture of the granitite
along the border, showing that the parts which we now see are well into
the interior of the original mass and not near the contact with the rocks into
which the granitite was intruded, for the reason that at the contact the
granitite would have cooled down more quickly and thus have induced
upon its crystals a more minute texture than exists in the mass, where
cooling went on more slowly.
Geographical conditions indicated by the basal arkose, Tlie foriUatioU of beds of arkoSe,
and the abundant reasons above cited for believing that the land on which
the Carboniferous beds were laid down had long been subjected to secular
decay and leaching, make it necessary to suppose that the grades of the
streams were too low for the removal of the products of disintegration as
fast as they were formed. The site of the basin, which appears to have
undergone depression at the time deposition set in, must have been pre-
viously without very strong contrast with the surrounding country, except
138 GEOLOGY OF THE NARRAGANSETT BASIN.
SO far as it was a lowland or valley, as Professor Slialer supposes it to
have been. That a long period of erosion or nondeposition had closed at
this time is abundantly proved by the marked unconformity of the Cai-bon-
iferous with the underlying terranes, this great stratigraphic break embrac-
ing, as above noted, all of Silurian and Devonian time, if not as well the
upper Cambrian at the beginning of this interval and the lower Carbonifer-
ous at the close.
Absence of iron oxides in the basal arkose. — Tlie prevailing whltlsh aud grayish hues
of the basal arkoses, and of the conglomerates immediately above them, are
in strong contrast to the often vivid reds of the overlying and occasionally
intercalated Wamsutta series to be described beyond. This, bleaching of
the first Carboniferous sediments appears, like the coloring of the Wamsutta
beds, to have taken place prior to transportation, and the two processes
may be said to be complementary to each other. The granitites along the
northern border, and almost everywhere adjacent to the portions of the
basin where the red series of strata occur, are strikingly red by reason of
the discoloration of one of their feldspars. This reddening is probably one
of the results of alteration through atmospheric decay, but it is difficult to
determine when this change in the feldspar began to take place in an effec-
tive way, for the granitites in the present superficial zone have at least twice
been exposed to meteoric waters, once at the beginning of the Carboniferous
deposition, when the shore line was creeping over the rock, and since then
when the Carboniferous covering was swept away and the rocks were again
bared to weathering. It is hardly possible to suppose that the decay which
has led to this reddening occurred in Carboniferous time, for the reason that
the pebbles of granitite found in the conglomerates of the red Wamsutta
series, or higher up, are, so far as I have observed them, never I'ed except by
absorption of the red paste in which they are embedded. The most reason-
able supposition which I am able to advance is that the superficial products
of weathering previous to their traiasportation in Carboniferous time were
leached of their iron salts, which penetrated downward. The first transpor-
tation of detritus affected the superficial leached layer, and thus the basal
beds came to be white, as we now see them. When erosion had stripped
away the bleached materials at the surface, it reached the highly discolored
rock beneath, as yet very imperfectly disintegrated, from which were pro-
duced the red beds of the Wamsutta series.
BASAL BEDS. 139
Absence of carbonaceous matter along the northern margin. AnOtliei" faCtOl' wllich haS glVeH
free play to the interchanges of the iron oxides above mentioned in their
effect upon the color of the rocks is the very general absence of carbo-
naceous matter, or coal beds, in the basal series. In proportion to the
amount of carbonaceous remains present in the strata, the colors due to
the difFerent states of iron are concealed.
Extent of the arkose zone. — There is Tcasou for belle viug that the arkose bed
is nearly continuous about the margin of the basin, and that its disap-
pearance is due to faulting or to original local conditions which prevented
its accumulation. To what extent the sheet of arkose extends beneath the
basin is not known, as the rock is not exposed in the anticlinal axes in the
central part of the basin, for the reason that erosion has not there cut
down to the base. The arkose, together with the associated quartz con-
glomerates, wraps around the tongue of granitite and associated igneous
rocks which form the Wrentham-Hingham uplift between the Norfolk and
Carboniferous basins, and I see no reason why the Carboniferous basal
sediments should not have been continuous over this area, so as to unite the
two sets of beds in the present distinct basins. Until it can be shown, as
Crosby and Barton believed in 1880, that the arkose and higher strata on
either side of this granitic mass were derived from it alone, and not carried
over on it as a sheet of sediment from some still more northern area, there
seems no reason for accepting the view that this anticlinal ridge rose above
the general level in Carboniferous time. There are no general facts to show
that the arkose was carried along shore by currents more in one direction
than another. If anywhere thicker than at other points, the arkose is proba-
b\j most developed in North Attleboro. In the eastern part of the basin,
and generally in the northern and eastern portions, there are many sand-
stones far above the base which would be denominated arkose, but they
are not to be mistaken for the mixture of quartz and feldspar of granitic
aspect which makes up the mass of the basal series. This arkose in some
instances differs but little from the original igneous rock whence it was
derived, except for the solution of the iron-bearing silicate, a slight tritura-
tion of the grains, and the intercalation of clearly stratified beds or occa-
sional waterworn quartz pebbles.
140 GEOLOGY OF THE NARRAGANSETT BASIN.
SUPRABASAL CONGLOMERATES.
The conglomerates which occur near the base along- the margin of the
basin are not precisely basal in the sense in which that word finds its most
exact use. At a few points conglomerates actually rest upon the basement
floor of granite, but they more usually overlie beds of arkose. The reason
for this order of deposits lies in the fact, before noted, that the granitic land
area was, in the beginning of Carboniferous erosion and deposition in this
field, so decayed at surface that pebble making did not go on until the layer
of disintegrated granite was stripped off. It is in full accord with this chem-
ical preparation of the sediments that we find the first conglomerates i^revail-
ingly quartzose and composed of quartzite — rocks which do not yield to
atmospheric decay so readily as the granite. On account of this sequence
in the deposition — first arkose, and then conglomerate — the term supra-
hasal conglomerate expresses more exactly than hasal conglomerate the
nature of the inferior pebble beds in the Narragansett Basin. Of these
suprabasal conglomerates there are a few noteworthy exposures believed
to be approximately on the same horizon. The beds are often composed
of quartz pebbles, the remnants of veins in the granitic border, the latter
rock occurring less abundantly than in the higher conglomerates. These
beds form the closest analogy to the typical Millstone grit which occurs in
the basin, and the following locality, being typical, has been chosen for the
type, although the relations to the arkose and the basement rocks are better
shown elsewhere.
Millers River conglomerate. — In tlic Valley of Millcrs Rlvcr, iu Cumberland,
Rhode Island, there is a broad exposure of conglomerate beds underlying the
red Wamsutta series. In this gray series there are tlu-ee or four thick beds
of conglomerate with small quartz and qnartzite pebbles. The best section
is exposed on the farm of Mr. James A. Miller. The thickness is here
unusually great, being as much as 300 to 400 feet.
South Attieboro exposure. — Bctweeu South Attleboro and Lanesville, in the
triangular area between the southern end of the great horseshoe fold of the
Wamsutta and the Pawtucket area of these rocks, is an exposure of hard
quartzose conglomerate, with quartz veins. These beds evidently underlie
the Wamsutta, which once arched over them. They are probably con-
tinuous with the Millers River outcrops on the northwest, though that
WAMSDTTA GROUP. 141
connection can not now be traced. A few bands of red slate occasion their
northern upper face
jenks Park exposure in Pawtucket. — A knob of finc grittj Conglomerate occurs
in the upper part of Pawtucket just west of the band of red slates belong-
ing to the Wamsutta series, and is, like them, evidently brought to the
surface by a fold.
Other exposures of the conglomerate occur along the northern margin,
and at various points southward, in the area investigated by Dr. Foerste.
THE WAMSUTTA GROUP.'
Devonian or Old Red Sandstone. Edw. Hitchcock: Final Report on the Geology of Massachusetts,
1841. Catalogue of Rocks in Agricultural Museum, Sixth Ann. Rept. Mass. Board of Agric, 1859,
Appendix, p. xxvii. Mass. House Doc. No. 39, 1853.
Carboniferous. Logan and Hall : Geological Atlas, 1865.
Devonian and undetermined. C. H. Hitchcock, 1871.
Carboniferous. Crosby and Barton : Am. Jour. Sci., 3d series, Vol. XX, 1880, pp. 416-420.
Cambrian. Shaler and Foerste, 1887. (At North Attleboro.)
Carboniferous. J. B. Woodworth : Am. Jour. Sci., 3d series, Vol. XL VIII, 1894. (At Canton Junction.)
The name Wamsutta series is applied in this report to the red strata a
part of which were mapped as Devonian by Edward Hitchcock. The name
is used in a geographical and lithological rather than a chronological sense,
for it is evident from an examination of the field that these red rocks are
local deposits in the northern part of the basin and in the Norfolk County
Basin, and are represented by ordinary gray and carbonaceous sediments
farther south. An exact correlation with these southern beds is not at
present possible. Along the northern margin the red series underlies the
Coal Measures. At Pawtucket it is interstratified with them.
The list of references at the head of this section will give the reader
an idea of the various opinions held regarding the age of these beds. The
typical area in North Attleboro was definitely shown to be of Carboniferous
age in 1887 by Dr. Foerste's heretofore unpublished discovery of Carbonif-
erous fossils in the area southwest of Reservoir Pond in North Attleboro.
' Wamsutta, a name proposed, but not actually adopted, for North Attleboro. The " Wamsutta
Mills" are situated within this town. Wamsutta was the oldest son of Massaaoit, chief sachem of
Pockanoket, brother and predecessor of King Philip. He was named Alexander Pockanoket by the
court at Plymouth, June 10, 1660. The term is used by Dr. Foerste iu his thesis on this field, a manu-
script report now in the library of Harvard University.
142
GEOLOGY OF THE NARRAGANSETT BASm.
RED ROOK AREAS.
There are eight areas in the northern, part of the basin in which reddish
rocks have a surface exposure, and in these they are brought to the sm-face
by strong folding. 1. In North Attleboro and the adjoining towns of Wren-
tham, Massachusetts, and Cumberland, Rhode Island, a large horseshoe-
shaped area wrapping about a knob of granitite in Hoppin Hill and the
North Attleboro Cambrian outcrops. 2. A small lens-shaped area extending
northeastward from Central Falls, Rhode Island, into Massachusetts. 3. A
still smaller area south of the last, extending northeastward from the gorge
/^rco now exposed Area probably now covered Araa pmbobly ero<iec^ au^oy
.— >■ OirectiOfts in which the formation c/ecrease^ in thickness
? Passible e'x/rosures
riB. 11 Map showing distribution of red sediments.
of the Blackstone in PaAvtucket. 4. A characteristic elongate narrow area
extending along the noithern margin of the main basin and traceable as far
as the North River in the town of Hanover. This area is probably con-
nected at the west with the succeeding. 5. The largest area of all, extend-
ing from No. 1, near Sheldonville, northward and eastward to Braintree,
forming the greater part of the strata in the Norfolk County Basin. There
are exposures in (6) Attleboro and (7) Rehoboth, and one in (8) Norton,
which may belong to a different horizon. I shall begin the account of these
fields with the area along the northern border of the main basin.
WAMSUTTA GROUP. 143
THK AREA ALONG THE NORTHERN BORDER.
The area of reddish aud chocolate-colored strata along the northern
margin of the basin, from near Burnt Swamp Corner eastward, is consid-
ered first for the reason that along this line there is indubitable evidence of
the relative positions of the red and gray rocks. Throughout the extent of
this northern margin the red conglomerates, sandstones, and slates occur at
or near the base of the Carboniferous formation, or are separated from it
by beds of arkose and gray quartzose conglomerates. The beds can be
studied along the border in Wrentham about three-quarters of a mile north
of the Shepardville reservoir, in two small hills lying west of the stream
which comes in from the north. Immediately south of a small contact
valley between the granitite and the Carboniferous beds of the border
appear red sandstones and slates. The rock is pervaded by two sets of
cleavage planes striking about in the line of the border, the dip of one
being nearly vertical and that of the other into the granitic terrane at an
angle of 70°. The attitude of the sedimentary beds is not very plainly
exhibited. Limited exposures of banding indicate a strike parallel with
the border and a southerly dip of from 25° to 30°. The outcrojjs in the
western knoll show red sandstones succeeded by greenish sandstone, which
in turn is succeeded by more red sandstone. Near this locality an old mill-
stone made out of a reddish conglomerate with small quartz pebbles was
seen in 1894 built into the fence. The greenish sandstones just mentioned
have a more extensive development in the North Attleboro area (p. 151).
The red beds are well exposed on the southern face of Foolish Hill in
Foxboro. They here dip steeply southward. The cleavage dips steeply
northward. Thin bands of red slate may be seen intercalated between
beds of whitish arkose. Red conglomerates with quartzite pebbles also
occur. The thickness of the beds is difficult to obtain with accuracy, but
it may be estimated at this point as upward of 1,000 feet.
Red beds appear to the east near the contact, at some points conglomer-
ates prevailing over sandstones. The thickness evidently diminishes toward
the east, but exact measurements are wanting. The red color of the basal
rocks also declines and becomes of a chocolate hue. The strata are rarely
deep red east of Brockton, though deep-red slates occur northeast of
Abington. In the eastern part of the field red conglomerates are no longer
recognized.
144 GEOLOGY OF THE NAERAGANSETT BASIN.
The relative paucity of granitic pebbles in the Wamsutta conglomer-
ates along the northern border is evidently due to the previously mentioned
condition of the gi'anitite at the time deposition set in. Nowhere is there a
sharper contrast between the arkose beds and the red shales than on the
southern face of Foolish Hill. Bands of red shale here alternate with the
arkose in a manner to show that the small particles of the shale brought
with them their coloring matter from the seat of denudation, as Russell has
argued in the case of the red beds of the Juratrias.^ The importation of the
oxide of iron subsequent to deposition would have colored the arkoses and
the shales alike.
About a mile southwest of Whiteville, shown on the Dedham sheet,
conglomerates occur dipping gently southward. The quartzite pebbles of
this rock are locally brecciated, and their surfaces exhibit a kneaded appear-
ance on the matched faces, showing clearly that brecciation has taken place
since deposition. The waterworn rounded surface of the original pebble
can be readily traced. These dynamic phenomena indicate that the strata
along this northern margin have never been under the pressure which has
so profoundly acted upon the elongated conglomerate pebbles near Newport,
Rhode Island.
The shallowness of the waters — if indeed the deposits were made in a
permanent water basin — over this area in Wamsutta time is shown by the
current marks on sandstone layers between Whiteville and Easton, and by
the coarseness of the sediments.
The structure of the beds is everywhere comparatively simple, their
dip being southerly beneath the carbonaceous strata which begin the Rhode
Island Coal Measures. Their continuity is frequently interrupted by faults
in the manner explained in the discussion of the boundary line from Burnt
Swamp Corner eastward.
Gray sandstones of the northern border. — In tlie Small hill uear tlio border uorthwest
of the Shepardville reservoir, in Wrentham, there are exposures of a brown-
ish, sometimes greenish, fine-grained, rather massive rock, which under the
microscope is seen to be composed of grains of clastic quartz and feldspar.
This rock is at present considered as a member of the Wamsutta series, and,
on account of its more extensive development a few miles soiithward, in
North Attleboro, may be called the Attleboro sandstone. The outcrops
' Subaerial decay of rocks, by I. C. Russell : Bull. U. S. Geol. Survey No. 52, 1889, p. 56.
WAMSUTTA GROUP.
145
along tile northern border are of much importance in that they help to
define the stratigraphic position of the rock, ft is here interbedded with
the red conglomerates and shales.
Traces of this rock are seen at points eastward in the area under dis-
cussion. Bowlders of a similar rock bestrew the hillside where the North
River passes from the Carboniferous area into the region occupied by the
granitites. Here the sandstone is well bedded and alternates with bands of
pebbles and slate. This variety of sandstone along the northern border is
apparently much thinner than in North Attleboro. The probably volcanic
origin of this rock, in the form of ash, is referred to in the account of the
occurrences about North Attleboro.
THE NORTH ATTLEBORO AREA.
The most characteristic exposure of the Wamsutta group occurs as a
horseshoe-shaped area, open on the north, in the towns of Wrentham and
Fig. 12. — Geological section nortiiward from Kobinaoii Hill,
North Attleboro, Massachusetts, and Cumberland, Rhode Island. The
formation is a series of conglomerates, sandstones, shales, and calcareous
beds with associated felsites, felsite breccias, felsite agglomerates, and
diabases. A characteristic of the area is the very great thickness of
conglomerates.
Beginning on the northeast, the formation makes its appearance abo^it a
mile northeast of the village of North Attleboro, in Robinson Hill (see fig. 12),
an eminence which overlooks the valley excavated in the softer strata of the
overlying Coal Measures extending westward from Mansfield. The section
MON xxxiii 10
146 GEOLOGY OF THE NAERAGANSETT BASIN.
from this point to the northern border of the main basin seems to have the
form of an overturned syncline, as shown in tig'. 12.
From Robinson Hill the red conglomerates, sandstones, and shales can
be traced southward, with strikes conforming in direction to the general
distribution of the formation, to Reservoir Pond, tlience to Rattlesnake Hill
and skirting the northern banks of Fourmile Brook. The formation thence
trends in a southwesterly direction to South Attleboro. Good exposures
may be seen in Red Rock Hill. Immediately west of Washington street
and south of Allen road, the sandstones and conglomerates may be seen
turning north-northwestward, whence they continue in that general direc-
tion as a broad area of red rocks with occasional exposures as far north as
the vicinity of Burnt Swamp Corner. A well-marked occurrence of these
rocks is found between Abbots Run and Millers River.
The stratigraphy of the area immediately west of the Blake Hill fault
block in Plainville, and thence northward to the Sheldonville narrows, is
imperfectly understood. About a mile north of the southwest corner of
the block, the Wamsutta beds occur in a well. Between this locality and
the Blake Hill schoolhouse, 1 mile southeast of Burnt Swamp Corner, gray
Carboniferous beds appear in an unknown relation to the red beds above
referred to. From the schoolhouse a strip of red conglomerates extends
southwestward toward the main belt of these rocks, which here skirt the
western border. The varying strikes and the repetition of isolated red and
gray outcrops northward in the direction of Red Brush Hill render the
structure of this region difficult of interpretation, since the gray beds may
belong below or above the red beds, and criteria for the determination of
then- position are there absent. The boundary line drawn upon the
accompanying map (PL XVH) between the red and gray series in this
region is therefore ^^'holly conjectural. It is probable that the rocks are
thrown into closed folds.
Conglomerates. — The couglouierates are composed mainly of waterworn
pebbles of greenish quartzite. One pebble in the outcrops in the valley of
Abbots Run contained several Obolus shells, which, according to Walcott,
are upper Cambrian. Granitic pebbles are common, and locally there is a
large proportion of felsite. Stretching and fracturing of pebbles under the
pressure of strong folding is evident from point to point in the more dis-
turbed areas. It is probable that conglomerates occur on more than one
'-' £
WAMSDTTA GROUP. 147
horizon in this field, but on a(;count of the intense folding, along with fault-
ing, it is not satisfactorily determined to what extent the conglomerates are
duplicated. Some of the felsitic conglomerates pass into agglomerates, and
these into felsite breccias, well shown in the valley east of Oldtown.
Sandstones. — The saudstoues of the area under discussion are of variable
texture, becoming coarse and feldspathic and thus approaching arkose
on one hand and grading into quartzites and shales by the separation of
the quartz and decomposed feldspar on the other hand. The reddish
quartzitic beds are well exposed on Robinson Hill and in general about the
village of North Attleboro. Their detailed representation on the map
accompanying this report has not been attempted. In the bend of the
sandstone ridges at Red Rock Hill, Mr. H. T. Burr found rain imprints on
the sandstone.
Shales. — The shales, or often slaty argillaceous sediments, of the for-
mation are well exposed in the valley between Reservoir Pond and Red
Rock Hill. Other exposures occur east of the village of North Attleboro.
Reservoir Pond appears to lie partly in a depression excavated along the
line of strike of these beds. The shales are frequently interrupted by
knobs and sills of felsite (see fig. 14). The beds contain flattened stems of
calamites, as at Attleboro Falls, near Reservoir Pond, and east of Red Rock
Hill.
THE CENTRAL FALLS AREA.
The Central Falls area is not well exposed. The best outcrops are near
the High School in Central Falls. On the east, near the old post-road, con-
glomerates occur with slaty beds in nearlj^ vertical attitudes. In Pawtucket
the beds are mostly red shales or slates at the same high angles. The
breadth of the formation decreases rapidly southward along the strike. At
the widest part it is as much as 1,000 feet. Its appearance in this part of
the field is evidently owing to compressed anticlines and synclines in the
highly inclined Carboniferous strata at the head of Narragansett Bay.
The structural relations of this area to that in North Attleboro ai-e best
explained by an anticline arching over the conglomerates west of South
Attleboro. This view also supposes that some of the Coal Measures, i. e.,
the Pawtucket shales, may be inferior in position to this southern extension
of the red beds.
148
GEOLOGY OF THE NARRAGANSETT BASIN.
THE PAWTUCKET AREA.
Another small area south of the last, not more than a few yards in
width, is exposed in the gorge of the Blackstone River, in the southern
part of the city of Pawtucket. At this point the red slates are associated
with green slates, recalling a similar association of red and green slaty
beds at Pondville, in the Norfolk County Basin. Close folding appears
also to be, in this locality, the explanation of the relations which these
beds bear to the adjacent carbonaceous beds. This is the southernmost
exposure of the red rocks known to me in the basin. Southward and west-
ward in this latitude the red rocks disappear. At only one point on the
Little Compton shore do red rocks appear at the surface outside of the
areas named, and in this instance they are limited to a thin layer of red
hematite in the coal-bearing' section. The deposition of the carbonaceous
series of the Coal Measures in this southern field preceded the incoming of
the red material from the north, and continued without interruption south
of Pawtucket.
RED BEDS IN ATTLEI50R0, REHOliOTH, AND NORTON.
These occurrences are fully considered elsewhere in this report. Rea-
sons will be advanced in the following chapters for regarding at least the
first two of these red beds as local deposits formed at different levels in
the Coal Measures. The last-named area contains red shales with calamites
in the drift a few rods soutli of the outcrop.
NORFOLK COONTV BASIN AREA.
No detailed work was done in this basin during the present survej^.
As a result of a reconnaissance, fossils were found at Canton Junction, con-
firming the views of Crosby and Barton as to the Carboniferous age of a
part of the strata. The rocks closely resemble the red and gray beds along
the northern margin of the main basin. Red beds largely predominate in
all the exposures. A characteristic basal section has already been described
at Pondville. The strata are almost everywhere inclined at very steep
WAMSUTTA GEOUr. 149
angles. While the section at Pondville indicates simple downfolding of
the margin, the form of the basin and the distribution of beds along the
border, particularly on the north, are suggestive of downfaulting of the
beds in most parts of the basin. The strata are usually not so much meta-
morphosed as those south of Pawtucket in the main basin. The occurrence
of locally metamorphosed conglomerates at Morrills Station (see fig. 6,
p. 120), on the Walpole and Wrentham Railroad, illustrates the effect of
great pressure in producing the elongation of pebbles and in inducing
secondary minerals. In this instance the rock has become very markedly
sericitic and disintegrates rapidly.
SOUTH ATTLEBORO LIMESTONE BED.
This name has been chosen for the occuiTence of nodular aggregations
of calcite and amorphous carbonate of lime which are associated with the
red shales of the Wamsutta or red rocks, and which are particularly well
displayed in South Attleboro, in the southern base of the hill at the foot oi
which the town is situated.
A section from the road northward up the hill is as follows:
Section of the Wamsutta formation in South Attleboro, Massachusetts.
Feet. In.
Eed shales, concealed southward 6 0
Fine conglomerate 2 0
Red shale 6
Limestone bed 6 0
Shales, red 10 0
Conglomerate 5 0
Shales, red, partly covered 119 0
Sandstone, red 24 8
Sliales, red, partly concealed ,. 99 2
(Felsite, reddish and irregular in thickness, exhibiting flow structure, 25 ft.)
Shales, red 28 4
Red conglomerate, coarse pebbles 60 0
Shales, red 60 0
(Diabase, amygdalar cavities on northern aspect, 15 ft.)
Eed shales, concealed northward, measured 175 0
The limestone occupies irregular kidney-shaped cavities in the red
shale, or is for a few inches of its thickness in the form of rude layers.
Another mode of occurrence is as isolated nodular masses half an inch in
diameter. Tliese nodules are frequently elongated in the direction of the
150
GEOLOGY OF THE NARRAGANSETT BASIK
strike. Some of the larger masses, where weathered, show minute rounded
apertures, marking closely set pits.
Under the microscope, in thin section, a specimen of the amorphous
limestone fi-om this locality appeared as an aggregate of minute grains,
occasionally exhibiting large individual grains with distinct cleavage.
Stratigraphically, the limestone is at this point relatively low down in
the red series of rocks. The material can be traced westward and north-
ward, by means of bowlders, in the same relative position on the east side
of the valley of Abbots Run.
Eastward and northward, limestone is again found on the place of Mr.
Todd, near the old Powder House, in North Attleboro ; but here the lime-
stone is a mottled marble, which has been used for making quicklime. The
limestone bed here occurs in a thick section of sandstones and shales of red
color, in no way identifiable with the section in South Attleboro. This
occurrence is on a more northern line of outcrop than the former, and if
stratigraphically connected with it, is to be explained by a fold such as is
suggested by the general structure of this area.
The irregularity of occurrence of the limestone in the different sections
where it is exposed, together with its evident secondary origin, has led to no
dependence being placed upon it in the course of the survey as a plane of
reference in the correlation of strata.
Similar shaly limestone reappears in the Norfolk County Basin, near
Canton Junction, Massachusetts, in a section described by me.^ A closely
similar rock occurs in the Cambrian section in North Attleboro, where the
limestone has evidently been formed from the remains of pteropods.
These limestones were described by Prof. Edward Hitchcock, and a speci-
men from the southwest part of Attleboro gave him the following analysis : ^
Analysis of limestone from Attleboro, Alassachitsetts.
CaCO:,
SiO-iandAljO, .
Quicklime
Specific gravity, 2. 71.
94.60
5.40
100. 00
52.98
■ Am. Jour. Sci., 3d series, Vol. XLVIII, 1894, p. 147.
2 Final Report on the Geology of Massachusetts, 1841, p. 80.
WAMSUTTA GROUP. 151
The late Prof. T. Steny Hunt suggestecP that these limestones inter
calatecT with red slates might correspond with those bands of limestone
which are met with in similar red slates and sandstones at the base of the
Carboniferous formation in Canada on the Bay of Chaleur and in New
Brunswick. It is clear that the deposits lie near the base of the Car-
boniferous in Massachusetts, but the evidence is as yet lacking that this
section corresponds, in the sense of an exact correlation, with the base of
the Carboniferous in the Canadian provinces.
Economically, these limestone beds, so far as they have been seen in
natural exposures, do not, in the presence of the larger and purer deposit
in the neighboring crystalline region of Rhode Island, assume a commercial
.importance. As a local source of supply for individual uses, they will
probably from time to time afford some employment.
ATTLEBORO SANDSTONE.
This is a fine-grained massive sandstone, varying from green to brown
in color, the latter hue being due evidently to oxidation.
The massive structure of this rock and the angularity of its particles of
quartz and feldspar in many cases, as seen under the microscope, make it
likely that it is to be regarded as a volcanic ash deposit, discharged from
the vents which gave rise to the felsite flows of this northwestern corner of
the basin.
The most instructive exposures of this rock are in the town of North
Attleboro. One may be seen just west of the water tower in the north-
eastern part of the town. A more extensive outcrop is exposed south of
Goat Rock and north of the Hoppin Hill granitic area.
Other occurrences of this rock are to be seen embedded with the red
series near Robinson Hill, north and east of the first-mentioned locality,
and again in the same stratigraphic relation in the vicinity of Deantown,
in Attleboro Township. The exposures along the northern margin of the
basin, in the Franklin quadrangle, show the position of the deposit to be
near the base of the Carboniferous formation. The quartz grains are there
much coarser than in North Attleboro.
The stratigraphic relations of the sandstone, where seen, indicate that
' Am. Jour. Sci., 3cl series, Vol. XVIII, 1854, p. 199.
152 GEOLOGY OF THE NARRAGANSETT BASIN.
it is a member of the Wamsutta series. Fossils iiave not been found from
which to determine the age of the beds independent!)'.
The texture and color of the rock, as well as its position and quantity,
would make it fit for building stone but for the fact that it is quite devoid
of those sets of joints or bedding planes on which the extraction of suitable
blocks depends.
IGNBOOS ASSOCIATES OF THE WAMSUTTA GROUP.
One of the striking features of the Narragansett Basin is the localiza-
tion of eruptive rocks in the area of the red strata of the Wamsutta group.
Dikes occur, however, elsewhere in this region, in Lincoln, near Providence,
and at the mouth of Narragansett Bay, marginal to the field.
Diabase. — Au interrupted faulted series of narrow, partly altered diabase
dikes can be traced from North Attleboro southward around the horseshoe
fold of the Wamsutta group to Lanesville and thence northward toward
Arnolds Mills. The diabase is usually erupted through red conglomerate,
sometimes in the form of twin dikes with a large sliver or wedge of the
country rock between. The upper surface of the diabase for a thickness ot
from 1 to 3 or even more feet is commonly vesicular; sometimes the lower
surface is amygdalar; but there is no evidence to show that the diabase
flowed out as a contemporaneous sheet.
These dikes are of variable widths from point to point where they
appear, attaining thicknesses of from 20 to 50 feet. They frequently rise up
as low black knobs, as between North Attleboro and Attleboro Falls, or
appear as low bluffs, as on the east bank of Abbots Run and between
Adamsdale and South Attleboro. For the most part they crop out along
the outer limits of the circular area occupied by the red rocks.
At a number of points these diabase knobs are so situated as to be
available for supphes of road stone, for which purpose they are superior to
any other rock in this district. The outcrops at Attleboro Falls are within
sight of the railroad, and there is a mass adequate for local uses free above
ground and now a hindrance to house building.
The ledge on the Henry Guild place in Adamsdale and its continuation
northward affords another source of suppl)^ — the nearest locality of trap in
workable quantity to the cities of Pawtucket ' and Providence. It would
require a carriage of a mile to place the material on the cars of the New
York, New Haven and Hartford Railroad at Adamsdale Station. To run a
WAMSUTTA GROUP. 153
spur of the railroad into the trap locahty would necessitate building- a
bridge or trestle across Abbots Run. From a point half a mile north of
the station, it would require about 4,000 feet of track to reach the ledge.
Quartz-porphyries, felsites, and granophyres. Intimately aSSOCiatcd witll tllC red
rocks of the Wamsutta group is a series of acid igneous rocks of felsitic and
grauophyric structure, the distribution of which is parallel with that of the
diabase dikes just described, and, like the former, these rocks occur in knobs,
whether true bosses or faulted and disjointed dike-like masses being not
easily determined. In general they are limited to the horseshoe fold, and
do not accompany the Wamsutta group eastward along the northern
Fig. 14. — Section tlirough felsite knob in Attleboro, Massacliusetts. (See table below.)
margin of the basin nor in the Norfolk County Basin beyond the narrows
in Wrentham. The felsites are usually of a reddish color.
A cross section (fig. 14) of one of these knobs south of Reservoir Pond
illustrates the general character of the association with the Wamsutta group.
The succession, beginning on the east, is :
Section south of Reservoir Pond.
reet.
Sandstone (red, pebbly) and shale (red) 40
Diabase 40
Felsite 10
Conglomerate, red 8
Felsite, in large knob 50
(Western contact not seen.)
154
GEOLOGY OF THE NAEEAGANSETT BASIN.
The felsites frequently occur higher up stratigraphically than the
intruded diabases. The following scheme of arrangement of rocks at three
localities will represent this fact:
Stratigraphic relations of felsite and diaiase at three localities.
(IT, Z.24.)
(VII, D. 20.)
(VII, B. 7.)
Red sliale.
9
?
9
?
9
i
Felsite.
Felsite.
Felsite.
Conglomerate.
f
Conglomerate.
Diabase.
Diabase.
Diabase.
Shale.
Shale.
Shale.
Conglomerate.
Conglomerate.
?
?
?
Diabase.
f
Conglomerate.
?
?
?
Shale.
?
?
Conglomerate.
This matching of short sections within 2 or 3 miles of each other, the
first two being within half a mile, illustrates something of the constancy of
occurrence of these igneous rocks. Regarded as a map, the bottom of the
table is east, the top west. The interrogation marks indicate the places of
concealed strata. The persistent failure of the western contact of the felsite
is a noticeable feature, due to the erosion and concealment of softer material.
The large felsite mass between the village of South Attleboro and Red
Rock Hill causes the strata to separate in the manner of a tilted laccolith,
but contacts have not been observed which verify the view that it is one.
Flow structure, often attended with crumpling of the layers, is manifest in
many outcrops of this rock.
Beneath the massive flow of the felsite is a zone of the same rock, form-
ing the matrix of an agglomerate, composed of rounded pebbles of felsite
and quartz-porphyry, together with quartzite and occasional pieces of horn-
blendic granitite. This lower bed is several feet thick. In South Attleboro
there is exposed a bed having a thickness of more than 10 feet. The water-
worn pebbles are evidently fragments caught up in a movement or flow of
the felsite over earlier conglomerates. The groundmass of this agglomerate
is porphyritic, with a plagioclase feldspar in every respect like that of the
overlying mass.
WAMSUTTA GROUP. 155
The eruptions of felsite in this field appear to have taken place some-
tivne after the deposition of the first sediments of the Carboniferous section
and before the laying down of the Coal Measures along the northern
border. These members of the quartz-porpyhry family of igneous rocks are
but outliers of more extensive eruptions of a closely related magma which
is extensively intruded into the rocks of the Boston Basin or is found there
as ancient flows. In that area the age of the eruptions is not precisely
known. If the evidence from the area of the Wamsutta group in North
Attleboro and the case in Plympton can be relied upon as evidence, it
would point to the Carboniferous age of these eruptives in the vicinity
of Boston, and probably to an epoch later than the lower Carboniferous
proper.
DIAMOND HII.L QUARTZ MASS.
Lying on the western border of the Wainsutta group, but apparently
developed in these Carboniferous sediments and in the felsites, is the large
mass of vein quartz known as Diamond Hill. The quartz occurs prevail-
ingly in the vein form, with layer upon layer of divergent pyramidal-faced
crystals. Locally the quartz is chalcedonic and wliite, earthy, opaline, the
whole being evidently the product of hot springs following the decadence
of igneous action in this ai-ea.
Quartz veins having the same structure and habit penetrate the red
sandstones of the Wamsutta group along the northern boundary in Wren-
tham. This habit of crystallization has not been detected elsewhere in the
basin, although extensive quartz masses occur at other points, as at Mount
Hope, and in less abundance southward in the bay region. It is highly
probable that the deposition of this quartz took place during Wamsutta
time.
WAMSUTTA VOLCANOES.
The peculiar features of the Wamsutta series — the rapid thickening of
the sandstones and conglomerates toward the northwest corner of the present
area, the felsites with definite flow structure, the gray ash beds or Attleboro
sandstone, the agglomerates of felsitic material, and the associated conglomer-
ates composed in large part of felsite pebbles — all point to a volcano or volca-
noes existing in this field in Carboniferous time. The known petrographic
connection between the flow structure of felsites in extrusive masses and the
coarser structure of typical granite-porphyries in stocks and dikes brings
156
GEOLOGY OF THE NAEEAGANSETT BASIN.
the plienomena of the Wamsutta sei'ies in North Atlleboro and the under-
lying terrane of schists with intrusive granite-poi'phyries in Cumberland into
an interpretable relation. On the one hand, we have the effusive products
of volcanic action; on the other hand, the underground conduits- and rents
filled with their equivalent portions of the magma.
The same story is fairly derived from the Blue Hill region on the
north side of the Norfolk County Basin. The beginning of sedimentation
in this part of the Carboniferous land area aptpears clearly to have been
accompanied by extensive acid eruptions. It is probable, as above noted,
that the large felsite area about Boston was formed also in Wamsutta time.
How much later the action continued can not be readily determined. The
intrusion of pegmatitic granites in the southern arm of the Narragansett
Basin, in the Aacinity of Watsons Pier, together with the marked local meta-
morphism of all the Carboniferous strata in that portion of the area, shows
that volcanic action held on there later than in the northern fields, if it did
M/7/ers /f/Ver Abbots Run
Hoppi'n /////
Fig. 15.— Geological
not altogether take place later than the deposition of the Carboniferous
strata in this part of the continent.
I'OLDING OF THE WAiMSUTTA GROUP.
The folds of the strata of the red Wamsutta series in North Attleboro
are the most complicated that have been found in the Narragansett Basin.
The large horseshoe-shaped area of red rocks above described wraps
around the older granitite and Cambrian rock of Hoppin Hill, so that
the general structure is anticlinal; but the dips of the beds are now
in many places inward toward the center, giving rise to an apparent
synclinal structure. On the east, from the village of North Attleboro
southward to South Attleboro, the dips of the red beds are mainh^ inward
toward the Hoppin Hill area, until at the latter place they become very
WAMSUTTA GEOUP.
157
low, as ill the nose of a broad shallow syncline (see fig. 15). On the
western arm of the area the dips vary from east to west. Such marked
inversion of strata warrants the explanation that the beds have been com-
pressed into the fan structure by the marginal collapse of a more or less
quaquaversal anticline which formed over the Hoppin Hill inlier. It is
owing to this extreme folding, together with the imperfection of the expo-
sures by reason of glacial di-ift, that the region is so difficult of interpreta-
tion. Northward, near Arnolds Mill, the apparent structure is indicated in
the section, fig. 16.
In the southern areas of red rocks in Pawtucket there is the most sat-
isfactory reason for believing that the broad exposures of alternating red
and gray rocks are due to close folding. This district, indeed, furnishes a
clue to the structure of the nearly vertical beds southward along the
w.s.w.
Fig. 10.— Geolugical section in the Arnolds ilill:
western margin of the Narragansett Basin, in the Cranston beds, and in the
equivalent Kingstown series, described by Dr. Foerste in another section of
this monograph.
This same field, showing the red and gray Carboniferous strata folded
into isoclinal relations, affords strong evidence for believing that the Wam-
sutta series, in the main basin at least, was not folded until the deposition
of the Coal Measures, and that the entire thick section of sediments in the
basin underwent phcation after the period of deposition. All the facts from
various points in the field support the view that there was but one period
of elevation, and not two, as was formerly thought by Edward Hitchcock.
There are a few disturbances along the northern margin in the Wamsutta
area, which have been thought to indicate an upturning of the red series
before the deposition of the Coal Measures in that section, but to my mind
the evidence is not clearly demonstrative of this view.
158 GEOLOGY OF THE NARRAGANSETT BASIN.
Several small faults exist in the North Attleboro area between Robin-
son Hill and South Attleboro. These dislocations are indicated by the
offset of diabase dikes along their line of strike, by the occurrence of beds
in blocks, and also bv the exposures in which the dislocation may be
traced. In front of the house of Mr. H. Rhodes, about 1^ miles northeast
of South Attleboro, reddish sandstones are brought against the red slates,
but this relation is probably due to local unconformity rather than to a
fault.
FLOHA OF THE WAMSUTTA (iROHP.
So far as the observations of the present survey g'o, the sole fossils
found in the red shales and sandstones of this series by Dr. Foerste and
myself are a species of calamites and a cordaites. As a whole, the strata
are prevailingly barren, a characteristic of red rocks everywhere. Enough
of the flora is known, however, taken together with the stratigraphy, to
warrant placing the beds in the Carboniferous section of the Narragansett
Basin. This fully confirms the views of Crosby and Barton expressed in
1880.
The geographical conditions under which the beds Avere laid down
seem to have been incompatible with the accumulation of j^lant remains in
the area of sedimentation, rather than that there is any difficulty in preserv-
ing fossils of this kind in red beds. In places abundant traces of calamites
occur in the form of good impressions without a trace of Carbonaceous
matter. In other localities the impressions of single stems are black with
carbon, and had enough of these fragments been accumulated in one plane
a black shale layer, if not a deposit of coal, must undoubtedly have resulted.
There are reasons for believing that southward beyond the limits of
the red beds plant remains were accumulating at this early stage in the
Carboniferous of the Rhode Island area. The general absence of fossils
in this series appears to have been due to a control exercised by the
peculiar processes concerned in the deposition of the series itself The pres-
ence of quartz-porphyry pebbles along Avith masses of this rock and the
related felsite, which appear to have come into their present relation to the
strata before the deposition of the Coal Measures in this part of the field,
suggests that volcanic action may have affected the formation of sediments
in a way to be locally unfavorable to the growth and preservation of plants.
THE OARBONIFEEOUS STRATA. 159
COAL MEASURES.
The Rhode Island Coal Measures, if we use this term to comprise all
the horizous on which coal has been reported, include at one point or
another in the basin all the strata from near the base to the great con-
glomerate bed which occurs at the bottom of the Dighton group. The
estimated thickness of this section is about 10,000 feet.
There is reason to believe that the lowest members of this great thick-
ness of sediments are, from Pawtucket southward, the time equivalents of
the Wamsutta group. The relations of the Wamsutta series of red and
green slates to the coal shales may be seen to advantage in the gorge of
the Blackstone River at Pawtucket.
The very considerable thickness of the beds between the basal arkoses
and the conglomerates and the overlying Dighton group of conglomerates
has rendered it possible to make certain divisions in this great middle section
which have a geographical value and indicate at the same time lithological
peculiarities. On these grounds four groups have been denominated, it not
being satisfactorily determined whether the strata of the lower two beds
are exactly equivalent or not.
The supposed relations of these to the beds recognized b}^ Dr. Foerste
farther south are indicated in the table on page 134.
In the following notes concerning the northern area local names will
be employed, with such chronological limitations as present knowledge of
the field will permit
CRANSTON BEDS: KINGSTOWN SERIES OF DR. FOERSTE.
PKOVIDENCH AREA.
It is the general opinion of those who have examined the rocks west
of Narragansett Bay in the ^dcinity of ProAddence that the strata of the
Coal Measures are here nearer the base of the series than those which lie
immediately on the east of Providence. This supposition is borne out by
the structure of the sections which can be drawn for this region.
The strata of this area from Pawtucket southward, to the limits of the
Providence sheet, exhibit generally very steep dips prevailingly eastward.
The strikes are generally east of north, being more persistent in the sand-
160
(lEOLOGY OP' THE NARRAGANSETT BASIN.
stone beds than in the shales, the latter being very much crumpled and
often striking east and west.
The metamorphism of this belt allies it petrographically with the area
southward in the lower part of Narragansett Bay. The sandy and pebbly
beds, however, exhibit less dynamic metamorphism, but the shales above
exhibit in a marked degree the development of new minerals which has
resulted from this change.
There are three well-marked north-south troughs about Providence
in which the softer argillaceous beds occur, separated by more resistant
arenaceous strata standing out as ridges. Beginning on the west, and next
\ See /f on A River
East Prov/dence
I Ten Mile River
Fig. 17. — Hypothetical geological section east aud west througli Providence, Khode Island, showing supposed relations of
Cranston and Tenmile River beds.
the escarpment which marks the crystalline and igneous border, there is
the depression between it and Sockanosset, Rocky, Sky High, Bradley,
and Windmill hills. The structure and character of the strata occupying
this depression can be inferred only from isolated observations, mainly in
the "dugway" in the southwestern part of Cranston, where the basal beds
of the Carboniferous cling to the escarpment in a recess. The next trough
on the east, which opens out into the bay south of Providence, is very
thoroughly filled in with glacial sand plains. The occurrence of conglom-
erates toward the south and the evidence from borings in the vicinity of
Providence are the sole indications of the stratigraphy.
RHODE ISLAND COAL MEASURES. 161
The coal from Cranston afforded F. A. Gooch the following analysis:^
Analysis of coal from Cranston, Rhode Island.
Per cent.
Water
0.24
4.49
82.20
13.07
Volatile matter
Fixed carbon
Ash
Total
100. 00
0.34
Specific gravity, 2.209 at 150-\
These trong-hs appear to be mainly underlain by coal-bearing- shales.
The Sockanosset mine in Cranston comes in this section. In the valley
north of Providence the shales crop out in a cut in the Old Colony
Railroad.
A well sunk in Butler street, corner of Bassett street, in 1895, penetrated
the Coal Measures. Samples of the materials brought up from certain
depths were furnished the Survey, through Mr. N. H. Darton, by Mr. C. A.
Ray, of East Providence, Rhode Island. The following table sets forth the
data obtained from this well.
Record of well sunk in Providence, Rhode Island, in 1895.
Depth in
feet.
Schist, soft, black, graphitic; with water turning to graphitic mud, somewhat
too gritty for lubricating j)urposes 126
Schist, micaceous, carbonaceous, carrying large cubical iron pyrites 176
Schist, carbonaceous 309
Schist, graphitic 341
Grit, or metamorphic sandstone 352. 5
Schist, graphitic, with fragments of vein quartz _ 419
Goal, anthracitic; very light, with small cubic fracture and some irregular
patches of dull black carbon 460
Coal, cut by veins of quartz, subflbrous near walls 475
Coal, with small cubical fracture and more of the dull lusterless carbon, about. 477
Schist, heavy, black, graphitic, pyritiferous, about 477
Schist, line micaceous, pyritiferous in layers ; 492
I Report of work done in the Washington laboratory during the fiscal year 1883-84 : Bull. U. S.
Geol. Survey No. 9, 1884, p. 18.
MON XXXIII 11
162
GEOLOGY OF THE NARRAGAJSfSETT BASIN.
Pawtucket shale
-Still farther northward in Pawtucket the shales are well
exposed in the banks of the Blackstone River on Division street, and at
Valley Falls they are exploited in a graphite mine.
The best natural exposure is along the eastward bend of the Black-
stone River between Central Falls and Valley Falls, where, on the south
bank of the river, a section of bluish and black carbonaceous shales, Avith
fossils, is thrown into a broken fold with minor contortions (see fig. 18).
The strike here is approximately east and west, and the dips are steep,
mainly 80° N. The beds evidently overlie the grits and red series half a
mile south. The slate layers contain distorted and disjointed fragments of
plants. Further evidence of the movement which the rock has under-
m»i mm
Fig. 18.— Folded and faulted Carboniferous shales on the Blackstone Eiver at Pawtucket, Khode Island. (Looking- east.)-
gone is shown in minute joints, in antiparallel sets, accompanying small
puckerings of the slate. Along each joint plane there has been a minute
fault movement of the normal kind.
The thickness of the beds included under the term Pawtucket shales,
if we place here all the soft beds in the troughs so far described, can not be
safely stated. If the structure about Providence is due to the duplication
of beds by overturned folds, as indicated in the theoretical section (fig. 17,
p. 160), and since there are at least 3,500 feet of beds between the sandstones
of the Avestern or Sockanosset ridge and the base or western boundary, the
apparently great thickness of beds in the other valleys may be readil}-
EHODE ISLAND COAL MEASURES. 163
explained. How much of this section is to be allotted to the shales alone
is not known.
sockanosset sandstones. — Tlic I'idgBS in this area, including the ridge in the
East Side area, are evidently due to the jDresence of sandstones and con-
glomeratic beds. They are well exposed on Sockanosset ridge east and
west of the reservoir. They are members of the Kingstown series of Dr.
Foerste. The shales are carried well up on the eastern flanks of these hills.
PI. V represents a side view of Rocky Hill, showing the glaciated northern
slope.
BAST SIDE AREA IN PKOVIDENCE.
Knowledge of the stratigraphy of this area is limited to a few out-
crops and to occasional borings, the latter of which have been recorded by
the Providence Franklin Society.^
The rocks consist of sandstones, shales, and pebbly beds, exhibiting the
aspects of metamorphism commonly found farther south at Sockanosset and
in the lower bay region. The schists are frequently highly carbonaceous.
The rock reported to have been taken from the ledge on which Roger
Williams landed is a black metamorphic shale, or ilmenite-schist, soft and
readily falling to pieces under abrasion. This rock evidently gives rise to
the depression in which the Providence and Seekonk rivers run.
The attitude of the strata in this area is exhibited in the outcrop
opposite No. 75 East George street, near Glano street. There are here
about 38 feet of slates with arenaceous and pebbly beds, all showing signs
of crumpling under great pressure and standing at angles of dip as high as
80°. The beds strike N. 25° E. magnetic (N. 14° E.), dipping in one place
E., in another W. The fine conglomerates contain quartz and quartzite
pebbles. There is a pronounced cleavage, for the most part striking N. 65°
W. magnetic (N. 76° W.), and dipping about 60° N. This secondary
structure seems- generally to have been taken by the inexpert for strati-
fication. Similar exposures exist on the hill to the west. Rock is also
reported to have been struck in borings at a few feet from the surface and
in making excavations for the reservoir. Coal is said to have been met
with on Benefit street south of Church and Stair streets.
On the land of the Swan Point Cemetery, between Swan Point road
and Blackstone boulevard, is a small outcrop of massive grayish sandstone,
i Geolosy of Ehodo Island, 1887, Addenda, pp. 129-130, 1888.
164 GEOLOGY OF THE NARKAGANSETT BASHST.
sucli as is characteristic of the Coal Measures on the east side of Providence
River. The rock exhibits a fissile structure, striking N. 25° E. magnetic
(N. 14° E.) and dipping 60° E. These figures give also, I believe, the
approximate attitude of the stratum
TENMILE RIVER BEDS.
The Coal Measures east of the Providence and Seekonk rivers as far
as the eastern bank of the Tenmile River afiFord characteristic exposures of
slightly altered sandstone, pebbly beds, and shales. Coal has been found in
the bed of Tenmile River. These strata may for reference be denoted as
the Tenmile River beds. The essential features of this horizon are set forth
in the following description of localities. If the beds on the west side of
the Seekonk and Providence rivers are, as the local structures indicate, in an
anticlinal relation with those on the east side of those streams, the meta-
morphosed shales and sandstone of the Cranston series are the equiva-
lent of the Tenmile River beds. For the present it seems best to consider
the beds as two geographical groups. The presence of the Odontopteris
flora and the insect fauna in the Tenmile River beds allies them, it should
be noted, with the metamorphosed strata at Pawtucket and Sockanosset,
and favors the idea that the two series are essentially at the same horizon,
though it is probable that the Tenmile beds do not, as does the Cranston
series, run downward to the base of the Coal Measures. (See fig. 17, p. 160.)
LEBANON MILLS EXPOSURE.
A low outcrop in which there is a small quarry occurs on the west bank
of the Tenmile River at Lebanon Mills. The beds are conglomerates,
sandstones, and slaty shales, striking N. 48° E. and dipping 70° S. One of
the slaty layers contains worm burrows and plant stems (Sigillaria, Cala-
mites), and the beds have here and there a reddish hue. The beds clearly
underlie those on the east bank of the river.
EAST PROVIDENCE AREA.
Very good exposures occur in the southern part of the town of East
Providence, Rhode Island, in quarries near Leonards Corners, and particu-
larly along the shore of Narragansett Bay from Watchemocket Cove south-
ward to near Sabins Point. The strata in this area are in marked contrast
to the exposures on the west side of the Seekonk and Providence rivers.
RHODE ISLAND COAL MEASURES.
165
G/ac/a/ drift
as regards both attitude aud alteration. They not only he in less disturbed
positions, but they preserve to a much greater degree their original clastic
texture, and fossils are of frequent occurrence in them. An account of the^
more typical exposures as they now exist follows:
Leonards Corner quarries. — In the soutlieastem triangle formed by the roads,
at an elevation of about 100 feet above the sea, is an exposure of pebbly
sandstone on the site of ■- a rock crusher. The strike here is about east-west
and the dip very gently to the south. An unidentifiable fossil tree, over 9
feet in length and from 6 to 8 inches in diameter, lies prostrate in the bed-
ding, with its major axis east-west.
A half mile east of the outcrop just described, about 25 feet of the
coarse pebbly sandstone of the Carboniferous are exposed in Mr. John
McCormick's quarry. The beds are massive, essentially horizontal, with
traces of coaly shales and coal, the last
mostly marking the sites of single plants.
The following plants were found:
Calamites suckovii, in large, well-pre-
served forms, showing inner markings.
One large specimen, somewhat flattened,
was preserved in a coat of wad, a replace-
ment of the cortical layer probably after
carbonate of lime. This stem lav nearly
east-west, as did others in the same quarry, biit the plants are disseminated
and occur at no particular level, indicating the occasional drifting in of
floating trees and the rapid accumulation of the sands and pebbles.
Sigillariaf Long, slightly tapering, flattened stems, with longitudinal
striations, but without cross markings, occur in this section, usually pre-
served as internal casts in sandstone. They may be ill-preserved calamites.
In the rubbish in the bottc m of the quarry, but evidently transported,
were fragments of shale with raindrop impressions.
The sandstone beds are traversed by a fault striking N. 44° W., with
a hade of 10° S., and the well-marked slickensides have a uniform pitch on
the exposed wall of 55° NW. This dislocation can not be of any consider-
able extent, for the same sandstones lie on both sides of the plane of divi-
sion. Another set of divisional planes, in the form of very close-set joints,
striking N. 46° E., divides the sandstone along a belt of variable width into
Fig. 19.— Sketch of zone of excessively jointed s.ind-
stones (SS), face of McCormick's quarry.
166 GEOLOGY OF THE NAREAGANSETT BASIN.
blocks too small for building purposes. (See fig. 19.) This zone of jointed
rock widens from not more than 2 feet at the present sui'face to 10 or 12
feet at a depth of 20 feet.
Section from Watchemocket Cove to Riverside. The rOcks wHch appear in the quar-
ries above described come to the seashore in bold clifi"s between Watche-
mocket Cove and Riverside, and in a few places the natural section has
been made clearer by railway cuts. About 100 feet in thickness of Carbon-
iferous sandstones, conglomerates, and shales are exposed along this section,
in the form of a broad, flat syncline from Watchemocket Cove to near Pom-
ham Rock, where the strata become vertical and are much distm-bed, at one
point the sandstone beds having been reduced to breccia. The strata just
south of Silver Spring form terraces overlooking the bay. Northeastward
from Pomham Rock and Riverside the same strata are seen inland in the
three ridges indicated on the topographic map. In the eastern one of
these long, low ridges, the sandy conglomerates dip northwestward at a
very low angle, but the strata in the westernmost of the ridges dip steeply
east, being along the line of the Pomham anticline. Northeastward, at a
point about a mile due east from Vue de 1' Eau, the strata turn more to the
eastward, as if in the canoe end of a syncline. (See fig. 20.)
Fig. 20 Geological section from "V^^atclieraoctet Cove to Riverside, "Rliode Island, showing the attitude of the Carbonifer-
ous strata. A, Kettle Point; B, Squantum; C, Silver Spring; D, Pomham Eock; E, Riverside; F, Outcrop near
Sherman Station.
South of Riverside the rocks are not well exposed. The details of
stratigraphy along this shore are sufficiently illustrated in the following
notes :
Halsey Farm section at Silver Spring. A feW rods SOUtll of SilvCr SpHug StatloU
the following section was measured in the bluff" at Halsey Farm:
Section in bluff near Silver Spring Station, Rhode Island.
Feet.
Sandstone and conglomerate (at top) 40
Conglomerate with pebbles of quartzite and granite 6
Sandstone (to bottom) 4
These strata are approximately horizontal, but farther east they dip
eastwardly, and westward across the railroad track they dip as high as
KHODE ISLAND COAL MEASURES.
167
45° E. In the railway cut the same series of strata show a north-south
vertical fault plane, the slickensid.es of which are horizontal. There is
Pig. 21 Geological section through rocky islets at Halsey Farm, Silver Spring, a, the rooky head shown in PI. VI;
R. R., the railroad.
present a coarse slaty cleavage, but it is not a constant feature. The
joint planes display great feathery surfaces of fracture, the divergent
lines of which indicate the direction of splitting; this sometimes is upward
or downward, but very frequently in a horizontal direction, the plane being
vertical. With certain precautions, the dip of massive beds can be obtained
by observing the inclination of the axes of these feather fractures. The
joint planes frequently die out with a convex front, the periphery being cast
into concentric flexures of conchoidal fracture, often measuring an inch from
trough to crest. These planes of fracture exhibit splitting figures having a
length of at least 6 feet from the rather indistinct point of origin to the
sharply incised marginal rugosities.-^
A few rods farther south, but north of Pomham Rock, is a small rocky
headland, composed of two distinct ridges, in which the following section
was shown, dipping 45° E., the same rocks reappearing in the islets north-
ward by the Silver Spring shore.
b o
c
Fio. 22.— Geological section of rocky headland below JiaUuy larni .;Uijir, mar Silver Spring, Rhode Island. (For expla-
nation of letters, see accompanying section.)
Section in rocky headland near Silver Spring Station, Rhode Island.
Feet.
e. Slate (at top) 15
d. Grits 15
c. Slates, partly covered 25
b. Grits and sandstones, with pebbles, isolated, and in bands and pockets 15
a. Slates with sandy layers, showing local unconformity to b, due to couteinpo-
raneous erosion; plant stems occur, and the upper portion of the bed is car-
bonaceous ; cross bedding very marked ; exposed above high-tide mark 6
' For a detailed description of this type of fractures, see paper "On the fracture system of joints,
ate," by the author : Proc. Boston Soc. Nat. Hist., Vol. XXVII, 1896, pp. 163-183,
1,68
GEOLOGY OF THE IfAERAGAKSETT BASIX.
Fossils. — North of the station black shales contain impressions of Sphe-
nojihi/Uum schlotheimii, both alone and with Asterophyllites equisetiformis.
Pecopteris, smaller than P. unita, also occurs here. In the mudstones on
the bluff calamites are abundant.
In the rocky points and islets along the shore near Silver Spring the
dips steepen to 45°, rising to an anticline arching over the upper narrow
end of Narragansett Bay — the southward continuation of the fold which is
more clearly indicated by the outcrops on the sides of the Seekonk River.
The southward extension of this anticline is not readily traceable. The
sandstones and conglomerates reappear in the ledge at the present mouth
of the Pawtuxet River, and
again at Rocky Point, on the
west side of the bay.
It is evident from a diag-
nosis of the dips in Provi-
dence and East Providence
that the strata in this section,
from the western boundary
eastward into the middle of
the basin, behave very much
in the manner of the layers
under horizontal pressure in
the clay models experimented upon by Mr. Bailey Willis.^ The general
structure of a cross section from back of Providence southeastward to
Riverside is represented in the accompanying diagram, fig. 23. It will be
noticed that there is a belt of A^ery highly tilted strata next the resisting
pre-Carboniferous teiTane, in which the effects of great pressure are mani-
fest also by the degree of metamorphism ; thence eastward lies a belt of
little-distui'bed strata without any marked metamorphism or even slaty
cleavage ; there come in then subordinate anticlines with a slight amount of
rock crushing. These two anticlinal axes correspond to what Mr. Willis
terms consequent and subsequent anticlines, respectively.
It is a noticeable feature of many of the folds in this part of the basin
that the inclination of the strata increases to a maximum near the axis.
Fig. 23.— Theoretical section of folded .structure on western margin of the
Narragansett Basin, a, Providence anticlinal belt; fc, East Providence
flat syncline; c, Pombam Rock anticline. (See PI. LXXXII, figs, f-i,
Thirteenth Ann. Kept. U. S. Geol. Survey, Part II.)
'The mechanicB of Appalachian structure: Thirteenth Ann. Rept. U. S. Geol. Survey, Part II,
1893, PI). 211-289.
EHODE ISLAND COAL MEASUEBS. 169
EXPOSURES IN THE TOWN OF SEEKONK.
The lowest strata exposed in this town occur along the east bank of
Tenmile River.
Section at Hunts Mills. — In December, 1892, a pit was sunk into the bed of
the stream at this point for the installation of a turbine water wheel. A bed
of coal in the following stratigraphic position was penetrated, the overlying
beds being exposed in the banks of the river:
Section at Hunts Mills, Rhode Island.
Feet,
Sandstone, of the graywacke type. Near tbe falls are large impressions of
unideutifled plant stems 40
Conglomerate, medium-sized pebbles, quartzose 5
Sandstone 10
Goal, anthracitic, showing slickensides, local crushing, and gash veins, with a
white asbestiform mineral 3i
Shale, black, varying from a fine-grained compact argillite to an arenaceous rock;
thickness unmeasured.
These strata dip gently to the north of east. The coal, uniformly like
that on the east side of the Seekonk River, is much less graphitic and
altered than that which comes from the west of that line in the metamor-
phosed belt. It is granular and is traversed by small quartz and calcite
veins. The strike of this bed would carry the coal along the present path
of the Tenmile River northward for several miles. No attempt has been
made to use this coal or to explore the underlying shales at other points in
this vicinity for other like deposits.
North of Hunts Mills, and about a mile south of Lebanon Mills, a
heavy -bedded sandstone crops out on the east bank of the river.
In the northern part of the town, strata approximately on the horizon
of the Tenmile River beds, and subjacent thereto, have been explored for
coal. One-fourth of a mile east of Perrins Station, on the Fox Point Rail-
road, is an outcrop of conglomerate and sandstone near the horizon of the
upper part of the Hunts Mills beds.
Perrins anticline. — Between Perrius and East Junction, in the cut on the
railroad to Fox Point, is an anticlinal exposure of the lowest beds seen in
170 GEOLOGY OF THE NAliRAGANSBTT BASIN.
Seekonk. The axis of this fold is probably that also of the great anticline
which lies between the Attleboro syncline and the Great Meadow Hill svn-
cline. The axial plane is overturned to the north. On the northern side of
the cut, sandstones and conglomerates dip NNW. at an angle of 45°; in
the southern half, sandstone beds with fossiliferous shales dip SSE. at
angles from 30° to 15°. There are no exposures at the point where the
anticlinal strata would be expected to connect the two parts of the section
in an arch, and evidence of an overthrust is wanting.
Fossils. — Several species of plants have been found in a good state of
preservation in the shales. The fronds of a species of Odontopteris are
usually graphitized and shining. One layer in the sandstones is covered
with the impressions of large Pecopteris fronds matted together, but show-
ing the spore cases. The following fossils were found at this locality:
Cordaites sp., Pecopteris unita, Odontopteris sp.. Catamites sp.
Bored well near Lebanon Mills. — About half a milc west of thc fossilifcrous beds
above described, on the land of Mr. L. W. Bourn, a boring was made
about fifteen years ago. The hole reached a depth of 705 feet 4J inches,
the surface of the ground being about 90 feet above sea level. The upper-
most stratum underlies the shale section in the Perrins anticline. The
following strata were passed through, according to a copy of the record in
the possession of Professor Shaler:
Geological column of diamond-drill hole made for the Seekonlc Goal Mining Gompany
on their anthracite coal lands, Bristol Gounty, Massachusetts, under the direction of
Thos. S. Bidgipay, geologist and mining engineer.
Feet. Inches.
Sand, gravel, and bowlders 54 0
Argillaceous slate, containing impressions of coal plants 4 0
Siliceous grit, alternating with argillaceous slates 13 6. 5
Graj' sandstone, micaceous, flue grained 9 9
Gray sandstone, coarse and flue, alternating with red, bluish, purple, and
olive-colored variegated shales 34 4
Sandstone, compact, bluish, containing seams of slate 17 4
Gray grit rock and sandstone, micaceous slates alternating 18 10
Bluish sandstone, micaceous, alternating with rock binds; lower part shaly,
containing impressions of coal plants 17 0
Gray micac> ous sandstones, with layers of grit rock and slate V2 9
Argillaceous rock and thin beds of sandstones with seams of slate 9 10
EHODE ISLAND COAL MEASURES. 171
Oeological cokimn of diamond-drill hole made for the Seelconk Goal Mining Company
on their anthracite coal lands, etc. — Continued.
^eet. luches.
Argillaceous rock, variegated, lower part thin layers of slate 12 0
Bluish sandstone 8 0
Sandstone, mustard-seed grit 24 0
Compact gray sandstone 7 4
Slate and sandstone alternating 8 6
Sandstone and grit alternating, mustard-seed grit 12 9
Sandstone, coarse and fine, micaceous, thin seams of slate 8 4
Argillaceous slates containing thin seams of coal and impressions of plants. 9 4. 5
Coarse and fine micaceous sandstones (depth, 288.5 feet) 6 9. 5
Conglomerate - 32 4
Eed conglomerate rock; slate containing streaks of coal; Gray sandstones
and coal slates alternating 8 3
Gray sandstones, coarse and fine micaceous, separated by argillaceous binds . 22 3
Rock binds and sandstones containing veins of quartz 18 0
Coal slates containing impressions of coal plants ; lower parts dark sand-
stone 7 7
Gray sandstone and argillaceous rock 8 0
Dark-colored sandstone and carbonaceous slate 7 0
Sandstone, micaceous, and coal slates containing impressions of coal plants. 10 0
Coarse sandstone, micaceous 8 10
Coarse sandstone, lower part containing thin seams of anthracite; sandstone,
micaceous and conglomeratic 14 5
Conglomerate (depth, 425.15 feet) 7 0
Gray sandstone, micaceous 13 4
Conglomerate 4 9
Gray sandstone and slate 3 11
Gray sandstone, micaceous, containing slate with plant impressions 8 2
Sandstone and slate, alternating, containing thin seams of coal 4 7
Fine- grained sandstone containing thin seams of slate and coal with impres-
sions 5 3
Coal slates containing coal plants; upper part sandy (depth, 479.15 feet). . . 7 8
Gray sandstone, fine grained, micaceous 13 6
Dark-gray grit rock 7 9
Slate and sandstone, 2 feet; dark-gray grit, 3 feet 4 inches; sandstone and
seam of slate, 3 feet 3 inches 8 7
Gray sandstone, 3 feet 5 inches; binds, 6 feet 7 inches 10 0
Gray sandstone . - - 6 6
Binds, 2 feet 7 inches; slate containing plant impressions; supposed thin
seam of coal, 2 feet 6 inches (depth, 531 feet 2.5 inches) 5 1
172 GEOLOGY OF THE NAERAGANSETT BASIN.
Geological column of diamond- drill hole made for the Seekonl: Coal Mining Comimny
on their anthracite coal lands, etc. — Continued.
Feet. Inches.
Coal slates with impressions, 2 feet 2 inches; sandstone and slates alternat-
ing, G feet 6 inches 8 8
Gray sandstone, micaceous, fine grained and variegated 48 10
Slate, 2 feet 7 inches; dark-colored sandstone, 4 feet 6 inches; supposed
thin seam of coal, 1 foot 8 inches (dei)th, 597 feet 5.5 inches) 8 9
Dark-colored micaceous sandstone - 7 5
Slate containing streaks of coal 4 7
Dark-gray micaceous sandstone and slate 11 8
Carbonaceous slate and trace of coal, 9 inches; fine-grained sandstone and
slate, 2 feet 4 inches (depth, 621 feet 1.5 inches) 3 1
Brownish micaceous sandstone - 5 3
Slate and sandstone 6 4
Dark-colored micaceous sandstone and slate containing calc spar in veins. . 8 11
Slate containing impressions of coal plants 7 9
Gray and brownish sandstones 7 10
Gray sandstone with bands of slate 7 9
Sandstone and slate 5 3
(Unnamed rock) 6 7
Slate and sandstone 8 5
Dark-gray sandstone, top roof, 7 feet 6 inches ; carbonaceous slates containing
impressions of coal plants, 9 feet 9 inches 17 1
Bed of anthracite coal ("?). (See statement below.) (Depth, 700 feet 7.5
inches.) 8 11
Slate containing vegetable impressions 4 9
The coal bed reported in the above table at the bottom of the hole is
said to have been a fraud. According to Dr. Arthur B. Emmons,^ "no coal
core was ever cut in the hole, and the coal core exhibited as having been so
cut was cut at the top of the hole from a piece of coal brought onto the
ground for the purpose."
In June, 1895, I visited the locality, and from an examination of some
of the cores then obtainable on the place was able to make out the dip of
the beds as varying from 10 to 15 degrees, figures which agree with the
southward dips of the strata on the same strike line in Perrins railway cut.
The red conglomerate which appears at a depth of 320 feet is suggestive of
the reappearance of members of the Wamsutta series ; but from a comparison
of the section of this portion of the Coal Measures it is difficult to conceive
'Trans. Am. Inst. Mln. Eng., Vol. XIII, 1885, p. 517.
EHODE ISLAND GOA.L MEASURES. 173
that all the red beds lying on the outskirts of the great Wamsutta mass
belong on the same horizon. In a red slate core there could be seen
annelid casts, such as characterize the red slates on the south side of the
Attleboro syncline (see p. 178). It is to be noted also that about 1 mile
northeast of Perrins cut the red series is exposed in the northeast comer of
the town of Rehoboth. Red shales here also contain annelid tubes.
The stratigraphic thickness of the boring, on the doubtful assumption
of the parallel dip of the beds to the bottom, is about 628 feet. There are
upward of 1,800 feet of measures to the highest exposures just above the
Seekonk conglomerate, and there are upward of 2,000 feet of concealed
measures from this horizon upward to Great Rock, where coarse conglom-
erates, supposed to be of the Dighton horizon, come in. This calculation
gives the group of Coal Measures below the Dighton conglomerate in this
section a minimum thickness exceeding 5,000 feet. If 5,000 feet of strata
below the Dighton conglomerate are measured, in the tyj^ical area on either
side of the synclinal axis in Dighton and Swansea, it will appear that the
bottom of the series is here by no means reached. I am therefore led' to
place the beds just described relatively high up in the Coal Measures.
SEEKONK BEDS.
About a mile east of the Tenmile River beds, and about 1,000 feet
higher up stratigraphically, is a series of monoclinal ridges of sandstone
and conglomerate which afford the best natural exposition of the Carbon-
iferous strata that is found anywhere in the inland portion of the basin.
While sandstones form the dominant exposures and leading topographical
feature of this series, shales enter about equally into the thickness of the beds.
West and south of the farm of Mr. Davis Carpenter these arenaceous
and gritty rocks rise from 20 to 30 feet in height, in an area of about
1 square mile, in five principal ridges, striking a few degrees E. of N. and
dipping E. from 20° to 30°. The aggregate thickness, including sandstone
and shale below a thick conglomerate bed, is somewhat less than 2,000 feet.
There is no evidence to show that the successive ridges are due to the repe-
tition of step faults bringing up a single bed. East of the stream on the
Woodard place, in the southeastern part of the area of exposures, a sand-
stone ridge has been quarried, the strata here affording rough, thick flags.
The large strike joints which occur here are very smooth and nearly ]3ar-
174 GEOLOGY OF THE NARRAGANSETT BASIN.
allel, but the dip joints are much less regular planes. One-fourth of a
mile west of this locality there is a long ridge of alternating grits and
conglomerates, probably the outcrop of the heavy conglomerate which
comes in more distinctly farther north. The beds are penetrated by nests
and veins of white quartz. In the shales underlying one of the sandstone
ridges impressions of calamites and asterophyllites were found in the course
of the present survey by Mr. W. E. Parsons.
seekonk conglomerate. — North of tliis area, about a mile along the strike,
the geological structure and topographical features are repeated. The See-
konk conglomerate bed here becomes more pronounced and can be traced
along the east bank of a small brook for the distance of a mile. It is from
50 to 60 feet thick, very massive, and contains quartzite pebbles from 3 to
6 inches in diameter. Where weathered the pebbles fall out of the matrix
readily and show little or no dynamic metamorphism. The resemblance
of this bed to the conglomerates of the Dighton group is very striking, and
the bed may be tentatively considered the equivalent of the coarse con-
glomerate which occurs at the base of this group. It is so represented
on the map.
The strata in the northern part of Seekonk turn northeast, and then
due east and pass into Rehoboth, and so continue on to the tract mapped
on the Taunton quadrangle. Very good exposures may be seen along the
road about half a mile north of the head of Wolf Plain Brook. A coarse
conglomerate north of the road in the edge of the woods is probably the
continuation of the Seekonk conglomerate. It is overlain by sandstones
and pebble beds which dip from 5° fo 10° S.
The strata just described in Seekonk and in the northern part of
Rehoboth, as shown on the Providence quadrangle, form the western part
of a broad, square-ended syncline. About 3 miles south of the point where
the Seekonk beds turn from northerly to easterly strikes they again strike
eastward to make the southern side of the Great Meadow Hill syncline.
Some minor folding appears between this point and Great Rock.
The southern part of Seekonk and Rehoboth is heavily drift covered,
and outcrops are from 2 to 3 miles apart and not in sufficient number to
give much value to the interpretation of the structure in this part of the
field. About 2 miles south-southeast from the Davis Carpenter place a
coarse conglomerate striking E.-W and dipping 80° N. comes in, over-
EHODB ISLAND COAL MEASURES. 175
lying sandstones, indicating the abrupt turning of the strata eastward in
the manner above referred to. Half a mile east and a little north of this
outcrop, coarse pebbly grits dip gently S., indicating minor folds in this part
of the tield. Whether these exposures are reappearances of the Seekonk
conglomerate and the associated thick sandstones is an open question.
The general structure of the area would place the strata at the top of the
Seekonk beds, and they are so indicated on the map.
Three miles due south of thpse outcrops are two isolated outcrops of
gray and locally pebbly sandstone. The westerly one forms a low roche
moutonnee on the land of Mr. Fred. T. Haskins; the eastern one, at the
corner of the road, forms a massive knob 25 feet high. In the southeastern
corner of the area represented on the Providence atlas sheet, in Swansea
and partly in Barrington, Rliode Island, are outcrops of sandstone and
conglomerate striking NNE.-SSW. and standing at high inclinations. At a
few points the sandstones rise into knobs 30 feet high. A slaty cleavage
is sometimes shown striking N. 56° W. and dipping N. Where pebbles
occiir they vary from half an inch to an inch in diameter. Between
these beds and the last-described outcrops there lies the broad, shallow
valley of the Warren River, partly drift filled and indicating the existence
of some underlying, softer, valley-making beds along the median or anti-
clinal line between the Dighton and Taunton synclines.
BEDS NORTH OF THE TENMILE RIVER IN ATTLEBORO.
Thus far there have been described a series of strata continuous along
their strikes on the south and east of the Tenmile River and along the
Providence River, and a section upward to the coarse conglomerates of the
Dighton group. Similar strata are less perfectly shown in Attleboro north
of the Tenmile River and the Perrins anticline. On the south side of the
stream and the axis named the beds dip gently southward, but wherever
they appear on the north they have steep northerly dips. On the grounds
of the American Millenium Association, near Hebronville, a well was sunk
10 feet in drift and 20 feet into a gritty sandstone, but the first ledges of
diagnostic value appear along the banks of the Tenmile River in Dodge-
ville, where sandstones are seen dipping steeply northward. Half a mile
west of the railroad station, and over 2,000 feet below the coarse conglom-
erate in the Attleboro syncline, is an isolated exposure of coarse gray
176
gp:ology of the narragansett basin.
conglomerate dipping- 70° N. About 60 feet of beds are exposed, showing
alternations with sandstone and slate. The pebbles of the conglomerate
are granitite, quartzite, and quartz, and range up to 6 inches in diameter.
This bed occupies a stratigraphic position on the north side of the Perrins
anticline roughly corresponding to that of the Seekonk conglomerate on
the south side of the axis, and raises the question whether the Seekonk
conglomerate is the coarse con-
glomerate elsewhere found at
the base of the Dighton group
or a lower conglomerate com-
pi'ised within the Seekonk beds
proper. Westward and east-
ward for many miles no rocks
are exposed along this northern
strike line.
Somewhat higher up in the
section, and over a mile north-
east of the last-named outcrop,
there are exposed, along the
Old Colony Railroad tracks at
Thatcher road bridge, 1 mile
south -southwest of Attleboro
station, about 40 feet of coarse,
gray, gritty, and often con-
glomeratic sandstones exhibit-
ing cross bedding and marked
local or contemporaneous ero-
sion. A bed of fine sandstone
20 feet thick was excavated,
evidently by a river, to the un-
derlying coarse pebbly beds, and then the area was covered up with
coarse sands. This feature can be relied upon to show that the northern
face of the strata was originally uppermost. The beds stand at high angles,
dipping north.
Contact of red and gray beds, with local unconformity. CrOSslug UOrthward OVCr a feW
feet of covered beds, we find a glaciated exposure by the roadside exhib-
Fig. 24. — Contemporaneous erosion, with unconformity, in the Car-
boniferous at Attleboro, Massachusetts. The pebbles shown in
the upper part of the diagram are identical with the red slate in
the lower part.
EHODE ISLAND COAL MEASURES. 177
iting a clear instance of local erosion following the deposition of red shales
and preceding the deposition of more gray beds. Angular fragments of
the red shale occur in the overlying gray beds, completing the evidence of
unconformity at this point. The structure is indicated in the accompanying
diagram of the locality (fig. 24).
A few feet stratigraphically below this level of contemporaneous
erosion and a few yards westward in the vertical beds is the well-marked
unconformity before ixientioned. It is partly concealed by glacial gravels,
but shows the cutting off on the west of about 20 feet of fine sandstones.
The continuation of these beds on the west of this ancient channel of
erosion is not exposed. The excavation or channel thus formed was subse-
quently filled with coarse sands, which also mantle over the fine sandstones
to the eastward of the ancient stream bank.
The phenomena of this horizon indicate clearly the fluviatile nature
of the sedimentation in this portion of the Carboniferous area. The deposits
may have accumulated near sea level, but under conditions in which the
streams were given steep gradients and large supplies of freshly eroded
detritus of granite and quartzite, as if in some mountainous lake or bhabar
district, such as that at the southern base of the Himalayas in India.
Red shales. — TliB red slialcs which now succeed the gray beds can be
traced southwestward along the southern side of the Attleboro syncline.
They alternate with gray sandstones, and where most distinctly shown have
an ascertained thickness of 60 feet. Strata which exhibit a reddish color,
however, continue upward in the section nearly to the base of the coarse
conglomerate which forms the nose of the syncline. On the land of Mr.
Joseph Fisher the following section is exposed:
Section near Attleboro, on Thatcher road.
Feet.
Eed shales aud sandstones with gray sandstone interlaininated (top not seen) 22
Sandstone, gray 8
Sandstones, grayish-green (quarried) 52
The red sandstones contain annelid borings.
A little higher up than these red strata is a coarse conglomerate. Still
higher up are fine conglomerates with pebbles of quartzite, granitite, and
quartz. (See PI. VIII.) The quartz is often deeply stained with iron oxide.
Overlying these fine conglomerates are the reddish-tinged strata mentioned
MON XXXIII 12
178
GEOLOGY OF THE NARRAGANSETT BASIN.
above. At the eastern end of the syndine shown upon the map these beds
mav be seen turning northward and westward, with cross bedding plainly
showing the original top of the strata. The use of cross bedding in deter-
mining the original position of strata depends upon the fact that where the
inclined "fore set" layers are somewhat eroded the succeeding layers rest
upon their truncated edges. The evidence thus derived from the cross
bedding confirms the view that these beds are on the northern side of an
anticline whose axis is shown in the Perrius cut.
These beds immediately below the coarse conglomerate also exhibit
worm burrows, trails, and current marks (see PI. IX), and, what is even
more remarkable for this basin, the imprint of raindrops on an ancient
beach or exposed flat. (See PI. X.)
Raindrop imprints. — The locality exhibiting raindrop imprints is about one-half
mile southwest of the crossroads at the canoe end of the Atlleboro syncline,
where the reddish micaceous
sandstones below the Dighton
conglomerate are exposed in a
quarry. The surface of one
la3'er is current-marked, with
the steep fronts of the irregu-
lar ridg'es facing southeast
when oriented with reference
to the horizontal position, the
beds now standing vertical at this locality. Over the current marks are
the imprints of raindrops. These records of former meteorological condi-
tions are on the northern and upper face of the vertical bed, and the
stratum is on the south side of the axis of the syncline, a position in every
respect consistent with the interpretation of the stratigraphic succession
advocated in this report. This is, so far as I am aware, the only locality
in the basin in which raindrop imprints may be seen in situ. The preserva-
tion of the record at this locality, where the beds have been pushed up into
a vertical attitude, indicates that at least locally the dynamic metamorphism
in the Rhode Island coal field has not gone so far as has been commonly
believed. The condition of the imprints in this case further shows that in
the folding of the strata there was, at least on this horizon, little or no wide-
spread shearing of layer over laj^er, an action which in other localities is
Fig. 25. — Diagram showing cross bedding. A, B, successively deposited
layers of cross bedding, or "fore-set" layers ; C, later layers, covering
the eroded surface of A, B ; a, a, a, a, erosion surfaces.
RAINDROP IMPRINTS AND WORM BURROWS ON VERTICAL CARBONIFEROUS STRATA, SOUTH FLANK OF
ATTLEBORO SYNCLINE.
Looking somh. Scale m inches.
RHODE ISLAND COAL MEASURES. 179
usually marked by miuute slickensides or the appearance of a "grain"
running up and down the dip in the direction of the shearing movement. A
slickensided fault plane in the bedding is shown at this locality.
Attieboro synciine. — One of the few points in the basin where the struc-
ture and superposition of beds are exhibited within a small area and in a
satisfactory manner is midway between Attieboro and South Attieboro, in
the elevation known as Ides Hill, lying between the Tenmile River and
Fourmile Brook. In this area of not over 2 square miles there is a well-
defined synciine in the Carboniferous strata, involving in the axis a thick
section of coarse com^jound conglomerates, immediately overlying the
highest of the rocks just described as lying north of the Perrins anticline.
The nose of this synciine is formed by the conglomerate, which stands up
as a low bluff at the crossroads 1^ miles southwest from the station in
Attieboro. (See PL XII.) The beds on the south side are vertical, and
can be traced along the entire area above described. The corresponding
strata on the northern side of the synciine are not so well exhibited. Near
the crossroads just mentioned, conglomerates exhibit a southward dip of
about 45°, and about 2 miles west, near Fourmile Brook, steep southerly
dips are again seen in conglomerate. Northward to the edge of the Wam-
sutta series the structure is not exposed.
It seems probable that this group of conglomerates belongs on the
horizon of the Dighton group, at the top of the Coal Measures in this basin
(see p. 184), the red rocks of the Wamsutta group on the north having been
brought up against these higher beds by dislocation.
Eastward of Attieboro and northward to the limits of the Providence
quadrangle in the directions named, the surface is too thickly covered with
glacial di'ift to make an interpretation of the under geology possible. The
area is, I confidently believe, underlain by Carboniferous strata, abundant
fragments of grayish conglomerates, grits, and sandstones occurring in the
drift. Judging from these erratics, which have not traveled far, con-
glomerates and the finer-grained rocks occur in this tract. The red Wam-
sutta beds may also be expected to reappear in this eastern area, folded in
with the gray rocks. Bowlders of this formation appear in the glacial drift
northeast of Attieboro.
Westward of the line of section above described there are two or three
well-marked knobs of sandstone and conglomerate on the east of the road
180
GEOLOGY OF THE NAERAGANSBTT BASIN.
from South Attleboro to Hebronville. These beds probably represent the
horizon of the Seekonk group on the north side of tlie Perrins antichne.
BLAKE HILL FAULT BLOCK.
The gray Carboniferous strata west of Plainville in Blake Hill exhibit
several small monoclinal ridges of hard sandstone and quartzose conglom-
erate with interbedded shales, here and there containing casts of calamites
and rarely other members of the Carboniferous flora. The most prominent
of these ridges has received the name of "Goat Rock." A detailed meas-
urement of the strata exposed in this bluff above the talus has been made
bv Mr. F. C. Schrader, to illustrate the character of the barren beds in this
section :
Section of Goat EocJc Cliff.
Gray sandstone (at top)
Conglomerate, gray, coarse, with irregular partings of black slate about
2 feet from base 12
Shale, dark and slaty
Sandstone, gray, varying to a pebbly grit 1
Shale, dark and slaty
Sandstone, gray, with a few small pebbles in middle of the layer
Grit, fine, pebbly
Sandstone, grading downward from above
Sandstone, hard, fine grained
Shale, slaty, with plant stems 1
Sandstone, very fine grained 1
Shale, slaty
Grit, gray and finely conglomeratic
Shale, dark slaty
Sandstone and grit -
Conglomerate, gray, gritty, and grading upward into next above
Sandstone, gray
Shale, slaty
Sandstone, bluish gray
Shale, black and slaty, with plant stems
Conglomerate, flue, gray, and gritty 1
Shale, dark and slaty, a mere layer
Sandstone, gray
Shale, dark, slaty
Sandstone, gray
Feet. Inches.
9
0
8.5
4
2
11.5
3.5
4
5.5
10
1.5
11.50
11
8.50
7
11
3
8
EHODE ISLAND COAL MEASUEES. 181
Section of Goat Bock (7/i^— Continued.
Peet. Inolaes.
Shale, dark, slaty, a mere layer .2
Sandstone, gray 5. 5
Shale, with fossils, grading into sandstone 4
Sandstone, slaty , 6. 5
Slate .75
Sandstone, a hard gray rock 4. 5
Grit, gray and hard 9
Sandstone, gray, with plant stems, and traces of finegrained dark slate . . 2. 5
Sandstone, subslaty, with plant stems :' 1
Sandstone, fine grained, gray 6
Shale, dark, slaty, trace .25
Sandstone, gray 3
Shale, dark reddish and slaty, with plant stems .75
Conglomerate, gray and gritty, rather line 2. 5
Shale, black and slaty, with plant stems 8. 5
Sandstone, fine grained, dark gray, and in places gritty .4
Shale, dark and slaty 5
Sandstone, gray 10
Conglomerate, fine and gritty 2+
Talus of covered strata 30 0
A noticeable feature in this section is the frequent alternation from
sandstone to shales within a very limited thickness. The coarse conglom-
erate forming the crest of the ridge exhibits a variety of pebbles, as regards
both origin and secondary strtictures. The pebbles are chiefly a fine-
grained whitish quartzite, often presenting slaty cleavage, the discordant
direction of which structure in juxtaposed pebbles is evidence of mountain-
building in this geological province prior to the Carboniferous period and
subsequent to the formation of the quartzite, which is probably of lower
Cambrian age.
Fossils. — The fossils found in place in this section are mainly imperfect
stems of calamites. In the drift in the vicinity of Goat Rock there have
also been found two species of determinative value, viz: Alethropteris and
Sigillaria volzii Bt.
The latter plant is stated by Lesquereux^ to be rare in the Coal
Measures of America, one specimen being seen by him from the Plymoutli
F vein in Pennsylvania, a horizon near the top of the anthracite field.
' Coal Flora, p. 492, PI. LXXII, fig. 11.
182 G-EOLOGY OF THE NAREAGANSETT BASIN.
Dr. A. F. Foerste also found in the sandstones of this area calamite trunks
6 inches in diameter.
Coal. — A bed of coal said to be 6 feet thick was met with in digging a
well on the land of Mr. Charles P. Simpson in the autumn of 1890. This
locality is in the southern part of Wrentham, near the Attleboro boundary
line and on the eastern face of Blake Hill block. (See PI. XL) The well
is reported to have passed through the following strata:
Section of well near Attleboro, Massaclmsetts.
Teet.
Sandstone 24
Coal, anthracite - 6
"Flinty sand rock," thickness unknown.
Westwardly, gray conglomerates ovei'lie the coal section, and east-
wardly sandstones crop out from beneath it. It is shown by these latter
beds that the dip is here gentle to the southwest. The outcrop of the coal
bed is about 260 feet above sea level and from 20 to 25 feet above the level
of the pond in the northwest part of North Attleboro. Southward of this
locality the Blake Hill block is probably cut off by a fault, as basal arkoses
come in at the distance of half a mile along the strike line. Northwestward
along the strike the conditions appear favorable for exploiting this bed along
the western side of the Plainville Valley.
Yet farther eastward, and lower down, micaceous sandstones crop out
along the roadside and contain impressions of trees of small size. At other
points along the southern edge of the Blake Hill block the waste from
highly carbonaceous shales occtirs in the glacial diift.
This block of strata dips throughout to the westward, the dip increasing
from near horizontality along the eastern boundary at Plainville to 30° and
45° along the western, ill-defined margin. The western contact is appar-
ently made with the red Wamsutta series. It appears as if this block,
over a mile in width and about 3 miles in length, had been thrust into its
relatively undisturbed position, while the strata around it on the east, south,
and west, as well as the beds beneath its eastern foot, had been thrown into
steep folds and even overturned. It will be noted that the Blake Hill block
lies north of and behind the Hoppin Hill granitite boss, around which the
horseshoe fold of the Wamsutta is l^ent.
The stratigraphic position of the block can be only vaguely stated.
RHODE ISLAjS^D COAL MEASUEES.
183
In succession and sediments it strongly resembles the beds which appear
in East Providence and Seekonk in the middle portion of the coal-beai'ing
series. The following is a more explicit accomit of the supposed faults
which form the block :
Blake Hill thrust plane. — If a line be drawu parallel with the Walpole and
Wrentham Railroad tracks at Plainville Station and a little west of the
roadbed, it will follow closely the boundary between the nearly horizontal
strata of the Blake Hill block on the west and the vertical strata of the
country on the east (see PI. XV), at the extreme western end of the Mans-
field syncline. Opposite the Plainville Station this boundary line turns
westward in the form of a small loop, inclosing several outcrops of the
nearly vertical slaty strata which extend into the area of horizontal beds at
the base of the Blake Hill block. It is evident from an inspection of the
relations of these two sets of rocks, so sharply contrasted as regards attitude
and secondary structures, that the vertical series passes westwardly beneath
w
B/oA& /////
E
^-^ ^s^
^^
Fig. 26. — Geological section of Plainville Valley and thrust plane.
the Blake Hill block. Both sets of strata belong to the Coal Measures'
but the evidence from fossils so far found is not sufficient to determine the
relative position in the normal sequence of beds.
The Mansfield syncline is overturned between North Attleboro and
Shepardsville, and the evidence in the field points to strong pressure
exerted from the south and east upon this region. It was probably a result
of this pressure that the Blake Hill block was thrust northward upon the
edges of the broken Mansfield syncline. The position of the strata in the
Blake Hill block in the system of folds before these were broken is hope-
lessly lost in the diverse structure of this troubled and now deeply eroded
area.
Faults occur in the Blake Hill block west of the Plainville thrust
plane and parallel with its outcrop. They are developed on a small scale.
These faults are shown by two classes of facts: (1) The monoclinal ridges
of hard sandstone and quartzose conglomerate which strike northwest are in
184 GEOLOGY OF THE NAREAGANSETT BASIN.
line with offsets in the Attleboro sandstone which bounds the block on the
south. Goat Rock itself is the highest of these monoclinal ridges. (2) An
earlier fault has brought the gray Carboniferous rocks down into a right-
angled contact with the massive Attleboro sandstones. West of the Goat
Rock section the red series is met with in a few outcrops and in a well on
the northwest. There is reason to believe, therefore, that a fault bounds
this block on the west so as to bring the red Wamsutta rocks up to the
surface. (See fig. 16, p. 157.)
THE DIGHTON CONGLOMERATE GROUP.
Roxbury conglomerate Edward Hitcbcock: Final Eepoit on Geology of Massachusetts, 1841, p. 538.
Reference has already been made to a coarse congiomerate bed
believed to form the upper limit of the Coal Measures. The name Dightou
conglomerate is here given to a group of coarse conglomerates, with alter-
nations to sandstone, found as the highest members of the Carboniferous in
Dighton, Somerset, and Swansea, in Massachusetts. The coarsest conglom-
erate bed is at the base of the formation. The rocks are better shown in
Swansea than in Dighton, but the latter place being better known and more
accessible for the purpose of examining these rocks, the latter name has
been chosen. A few areas of coarse conglomerates elsewhere are referred
to this horizon.
The Dighton conglomerate group attains where most developed a thick-
ness of about 2,000 feet. Its Carboniferous age is not definitely proved,
but it is assumed on the following grounds: The Dighton conglomerate
directly overlies the Coal Measures. It is not derived from the erosion of
underlying Carboniferous beds, but it contains larger pebbles of upper
Cambrian quartzites than are known elsewhere in this field lower down in
the Carboniferous section. It difiFers from other Carboniferous conglomer-
ates only in that the fragments, being of larger size, demand for their trans-
portation more vigorous processes than those previously active. The beds
participated in the folding which closed the Carboniferous, and there is no
known unconformity between the Dig'hton conglomerate and the subjacent
strata. A typical outcrop of the coarse quartzite cong-lomerates of this
Dighton group may be seen in the crossroads nearest the southwest base
of Great Meadow Hill. One quartzite pebble, 8 inches long, contains the
brachio]3ods of the upper Cambrian fauna.
DIGHTON CONGLOMERATES. 185
In this northern part of the basin the several exposures of conglomerate
referred to the Dighton group lie in the inner or upper part of synclines.
This is true of the Great Rock area in Rehoboth, whence the rocks extend
eastward to "Rocky Woods," near Taunton. Another, and perhaps the
best area, is that of the Dighton syncline, extending from Dighton into
Swansea. Another well-defined syncline in which these beds are found
forms Ides Hill, west of Attleboro village. The coarse conglomerates at
Purgatory and Paradise rocks, in synclines near Newport, resemble the
rocks of this horizon.
The outcrops of coarse conglomerates at Swansea Factory and imme-
diately west appear locally to strike northwest and dip north, indicating
either that the great syncline is overturned southward or that there is here a
local folding along the northern side of the major synclinal fold. Outcrops
are too few to verify either hypothesis, but the high inclination of the
observed strata southward below the Dighton group shows that the beds on
this northern side of the synclinal axis stand at much higher angles than
do those on the southern side. The Great Meadow Hill syncline is nearly
symmetrical, but the Attleboro syncline on the north is unsymmetrical,
with vertical dips on the south side of the axis.
The Dighton conglomerate is composed mainly of grayish and green-
ish quartzite pebbles in the southern areas; toward the north, as in the
Attleboro area, it is equally rich in granitic pebbles. The amount of
quartzite in this group must represent several hundred feet of strata
stripped ofP the adjacent country in Carboniferous times. Many of the
pebbles are fossiliferous, carrying the upper Cambrian fauna already
described. The pebbles vary in size from a fraction of an inch to rounded
waterworn cobbles a foot in diameter. The reduction to spheroidal shapes
apparently indicates their passage through the surf' line on a beach. (See
PI. xni.)
In many sections the pebbles are packed together with the pellmell
structure of glacial till; the paste is often earthy and ferruginous, and
when slightly attacked by weathering allows the pebbles to roll out; in
other sections pebbles and paste are thoroughly cemented, so that the rock
breaks up only along joints.
Now and then a pebble shows a joint recess where the rolling action
did not continue long enough to reduce it to the form characteristic
186 GEOLOGY OF THE NARRAGANSETT BASIN.
of wear on a beach. The frequency with which this occurs in the larger
pebbles suggests that when submitted to the action of the waves the bits
were angular joint blocks, such as quartzites affoi-d when broken out of a
cliff. (See photograph of one of these joint niches in pebbles, PI. XIV.)
Here and there an indented pebble may be seen.
The Dighton group of conglomerates being the highest member in
this basin, the areas in which it occurs are, owing to the deep erosion of the
basin, somewhat removed from the present margin. The distance is gen-
erally from 3 to 4 miles.
The topography of these conglomerate areas is bolder and more rugged
than that of the other rocks in the basin outside of the Wamsutta series.
The formation abounds in rounded, bare, rocky knobs, with steep vertical
bluffs facing outward from the sj^nclinal axis over the area of the Seekonk
sandstones, again overlooking recesses in the formation itself Long rocky
ridges also abound, as in Dighton, Taunton, and Attleboro, now generally
given over to woods on account of the scarcity and infertility of the soil
and the general unsuitableness of the surface to agriculture.
The conglomerate masses attain elevations of 150 to 180 feet above
sea level, or of 80 to 100 feet above the surrounding level. In Swansea
the conglomerate ridges rise to 160 feet; in Dighton, to 180; and in Attle-
boro, also to 180. Near Taunton, the Rocky Woods attain an elevation of
160 feet. This level, indicated by the elevation of the conglomerate ridges,
is someAvhere near that of the Jura-Cretaceous peneplain were it extended
eastwardly over the Carboniferous area. The excavation of the strata
below this level must be attributed to erosion in the Tertiary period.
These conglomerate areas contain the headwaters of numerous brooks,
but several of the larger streams in the southern part of the field flow
across them, evidently from original courses which have been superposed
on these hard rocks.
It remains to be determined whether there is an unconformity betwe ^n
the Dighton conglomerates and the subjacent Seekonk group. It is to be
expected that even within the same geological period such discordances
would exist where currents were developed strong enough to urge cobbles
a foot or more in diameter out over an alluvial plain like that formed of the
Coal Measures. The original thickness of the group is also a matter for
further investigation. Were there higher Coal Measures in this area? And
COAL MEASURES OF THE DEDHAM QUADRANGLE. 187
did Permian or later strata overlie them ? There is a chance that in the
center of some one of these synclinal areas higher beds than have here
been recognized may be discovered. It is indeed possible that the whole
of the Dighton series is of Permian age.
The contemporaneous flora and famia of the conglomerate are as yet
practically unknown.. The brachiopods and Avorm burrows reported in the
quartzite pebbles belong to the upper Cambrian famia. (See p. 109.)
EXTElSrSIOlSr of the coal measures north AXD EAST OF TAUjSTTON.
Having described a typical area of the Coal Measures and the over-
lying conglomerates in a part of the basin where evidence of their structui'al
relations can be had, it is now purposed to describe the eastern extension of
these rocks, where the structure is less well understood. For convenience,
the order of presentation which is suggested by the mapping of this portion
of the field in sheets of the atlas folio will be followed, for the reason that
within the limits of these maps, comprising the Dedham, Abington, Middle-
boro, and a part of the Taunton quadi'angles, the exposures of strata are too
few in number and extent to permit any systematic account of the stratig-
raphy. These rocks have been described with more fullness than their
importance apparently deserves, partly for the reason that they have not
been heretofore described, and partly because they are the sole indications
of the under geology of the eastern part of the Carboniferous field.
DEDHAM QUADRANGLE.
The Carboniferous rocks of the main basin cover the larger part of
the southern third of this quadrangle. After we pass southward and
geologically above the rocks immediately along the border, outcrops
are too few to give more than a very general view of the stratigraphy.
The Coal Measures are present in Mansfield and West Bridgewater, and
probably underlie the intermediate towns. The surface, outside of the
glacial sand plains, is strewn with flaggy micaceous and feldspathic sand-
stones suggesting arkoses, winch agree in character with some of the out-
crops. A few conglomerate bowlders of the gray series occur, but never in
the abundance which characterizes the proximity of the coarse Dighton
group in other parts of the field. There is also absent the hilly and rough-
ened topography which accompanies these latter beds when they occur in
188 GEOLOGY OF THE NAERAGANSETT BASIN.
synclinal areas, and it is evident that these upper portions of the Carbon-
iferous have disappeared by erosion from this northern field. The rela-
tively gentle dips along this margin, together with the observed great
thickness of the formation where fully developed, would carry the outcrop
of the uppermost beds several miles south of the border and out of the
Dedham quadrangle.
The structure of the strata in this area, so far as it can be made out
from observed outcrops, is mainly synclinal. The axis of this fold passes
approximately through Mansfield Jtuiction and South Easton; or, in general
terms, lies at a distance of from 2 to 3 miles from the northern border.
The trough is broad and shallow toward Brockton, but its sides steepen
westward toward Mansfield, and between North Attleboro and the border
it is much compressed, and the folded strata are finally lost to view beneath
the block at Blake Hill. Its general features in the Mansfield area are
shown in fig. 27, on p. 190. The following- observations set forth the evidence
in typical areas, about Mansfield and Bridgewater:
MANSFIELD AREA.
There are no surface exposures in the immediate vicinity of the West
Mansfield coal mines, the rock having been found in digging a well. The
lowest strata of the Carboniferous appear nearly 4 nules north of the coal
mines, dipping gently off" to the south from the hornblendic granitite of
the A¥rentham-Hingham uplift. The basal arkoses and grits, described with
the Wamsutta series (pp. 135-139), form conspicuous ledges on the southern
face of Foolish Hill, in Foxboro. The Wamsutta series has here a possible
thickness of 1,000 feet. It is succeeded on the south by quartz pebble
and quartzite conglomerates and gray sandstones, forming glaciated ledges
scarcely above the general surface of the glacial drift. Southward from
Foolish Hill toward Mansfield Junction, beds of sandstone and conglom-
erates appear, dipping about 25° S. A roche moutonne'e gives the follow-
ing section from the top:
Section of a roche moutonne'e in the Mansfield area.
reet. In.
6. Saudstone, with layers of slate pebble cougloiuerate 6 6
4. Saudstone 3 6
3. Couglomerate, with slate pebbles 1 0
2. Saudstone 5 0
1. Conalomerate, base not seen 10 0
COAL MEASURES OF THE DEDHAM QUADRANGLE. 189
These beds dip to the S. 30° ; the cleavage dips N. 50°. The exposure
is noteworthy in exhibiting preexisting dark slates, broken "up and deposited
at this time. The slate fragments are angular and conspicuous elements in
the layers in which they occur. They vary in length from 3 to 4 inches
and in thickness from 1 to 2 inches. The attitude of the fragments and the
unruptured state of the stratum, except for joints and cleavage, preclude the
formation of the slate fragments by tire disruption in post-Carboniferous
times of an original argillaceous layer. For similar reasons, the fragments
are not to be regarded as contemporaneous pockets of argillaceous sedi-
ments. In the absence of contained fossils or other evidence of the age
of these pebbles, there is doubt whether they are fragments of the
subjacent Carboniferous shales or are detached pieces of the dark slates of
middle Cambrian age, remnants of which occur at Braintree, in the Boston
Basin. The not infrequent occurrence of signs of contemporaneous erosion
in the Cai-boniferous beds in the basin leads me to conclude that the con-
glomerates are of the class called " intraformational " by Walcott.^ I have
already described a limited occiu-rence of this kind at the contact of red
and gray beds in Attleboro. North and east of the junction at Mansfield
occur a few outcrops of conglomerate with small pebbles and associated
sandstones. At the junction are two exposures of grayish feldspathic sand-
stone— massive beds, like the typical sandstone ridges of the Seekonk
formation. The knob west of the railroad carries the flattened impression
of a large tree, and the rock in the railroad cut is much shattered.
One and a half miles south of the Junction is a locality where coal was
formerly mined (see PI. XVI). In the absence of surface exposures, and
because of the abandonment of the old shafts, it is impossible to get other
data concerning the structure at this locality than those furnished by the
records of earlier surveys and by one recent boring. From the Massachu-
setts report^ it woidd appear that the beds here strike NW.-SE. and dip
NE. from 30° to 35°, or as high as 45°, and in another place that the
strike of the beds is NE.-SW.; but the observation of C. T. Jackson,^ that
the "strata between which the coal beds are included run quite uniformly
'C.D.Walcott: Bull. C4eol. Soc. Am., Vol. V, 1894, pp. 191-198; Bull. U. S. Geol. Survey No. 134,
1896, pp. 34-40.
- Final Report on the Geology of Massachusetts, 1841, pp. 133, 540.
3 Geology of Rhode Island, 1840, p. 107.
190 GEOLOGY OF THE ISTAREAGAKSETT BASIN.
ENE.-WSW., and dip to the NNW. 53°," is, in my opinion, approximately
accurate.
Both C. T. Jackson and Edward Hitchcock agree in giving a northerly
dip to the rocks at this point, from which it is evident that the Mansfield
coal beds occur on the south flank of a syncline, and may be expected to
reappear on the northern side of the axis or in the vicinity of the Junction.
The probabilities are, however, that the sediments in this direction become
coarser as the shore line is approached, and that the coal beds either thin or
entirely disappear. The coal in Foxboro reported by Edward Hitchcock,
nevertheless, may be a reappearance of the coal on the northern side of
the axis.
One and a half miles south-southeast from West Mansfield Station, in
the Taunton quadrangle, red and gray sandy slates occur with nearly
vertical dips striking N. 64° E., indicating, along with other outcrops
described in connection with that atlas sheet, the much steeper southern
side of tlie syncline and the passage to the adjoining anticline. The accom-
panying section (fig. 27) represents the known and inferred portions of the
structure through the Mansfield area:
Fig. 27.— Section of tlie Mansfield Coal Measures. The lines represent obaerved beds and their underground extension
A, Foolish Hill granititei B, "Wamsatta series; C, Mansfield Junction. D, West Mansfield mines. E, vertical strata
south-southeast of last.
Analyses of two coals met with at depths of about 90 and 850 feet,
respectively, in a boring put down near the old Hardon mine, have been
COAL MEASUEES OE THE DEDHAM QUADRANGLE.
191
published by Dr. A. B. Emmons.^ In the annexed table, analysis No. I is
from the 90-foot coal, and No. II from the 8.50-foot bed.
Analyses of coals front the Mansfield area.
Water
Volatile combustible .
Carbon
Ash
Sulphur
Fuel ratio (
Carb. \
Vol. comb, y
1.02
3.76
74.24
20.97
99.99
.56
3.08
6.22
79.68
11.02
100. 00
Thin sections from the core made in this boring, according to a
manuscript report b)^ Prof. Collier Cobb, showed that the amount of meta-
morphisni varies Avith the depth, being greater at the bottom than near the
surface.
Flora of the Mansfield section. — TliB followiiig plauts liave becii rcportod from
the shales at Mansfield:
Prof. Edward Hitchcock^ figured forms referable to the genera —
Pecojiteris.
Sigillaria.
Cordaites (a form close to C. robbii.)
Calamites.
Si^henopbyllum.
Asteropliyllites.
Auuularia.
Leo Lesquereux^ has described:
Sphenopteris salisbnryi (n. s.).
Ehacophyllum adnasceus.
Teschemacher* described and named several forms, some of which are
of doubtful identification:
Pseudopecopteris irregularis.
Neuropteris angustifolia.
heterophylla.
Pecopteris loschii.
borealis.
Pecopteris gigantea.
Sphenophyllum truncatum (said to be un-
known except to Teschemacher).
Sphenophyllum dentatum=erasum.
'Trans. Am. Inst. Min. Eng., Vol. XIII, 1885, p. 515.
- Final Report on the Geology of Massaohusets, 1841.
' Providence Franklin Society Report on the Geology of Rhode Island, 1887.
•'Boston Jour. Nat. Hist., Vol. V, 1846, pp. 370-385.
192 GEOLOGY OF THE NABRAGANSETT BASHST.
BRIDGEWATEE AREA.
The available exposures from Brockton soiitliward through the Bridge-
waters indicate a broad syncline with low dips, and hence a much more
shallow trough than that near Mansfield. Southerly dips are found in out
crops from the granitites north of Brockton for a mile or more to the south
of that city. At Cochesett, and thence southward, northerly dips are
encountered as far as the northern part of the Taunton and Middleboro
quadrangles, in the vicinity of Scotland, about 3 miles south of the limits of
the Dedham quadrangle.
Ovei'lying the chocolate-colored sandstones at Brockton, described
tinder the head of the Wamsutta group, occur arenaceous and argillaceous
strata of slaty structure. Exposures of a bluish coarse sandstone have
been made in opening new highways northwest of Campello, at the corner
of Adams and Center streets. One and a half miles south-southeast from
this locality, on the west side of Salisbury Plain River, bluish-green slates
form a small outcrop. The cleavage is E.-W., and dips 45° N., the pre-
vailing direction and steep dip along the northern border. Bowlders of
grayish sandstone occur in the vicinity.
Going southward across the strike, the next exposure is in the railway
cut a mile east of Cochesett Station. The strata here dip from 5° to 10°
N., and aiford the following section from the top downward:
Section east of Cochesett Station.
reet.
3. Conglomerate ; pebbles of quartzite aud smoky quartz 10
2. Sandstone and arkose, gray . 10
1. Sliale, blue and comj^act 10
A thrust plane, with slickensides trending N.-S , was noted on one bed,
and there are to be seen sn^iall vertical quartz veins containing cavities lined
with botryoidal limonite.
About a mile south of the Cochesett exposure, coal is represented to
have been found, in the area between the Hockamock and Town brooks.^
The place of this bed would be at a depth of about 1,800 feet beneath the
Cochesett section.
1 Edward Hitchcock: Report, 1833, p. 277; Final Report, 1841, p. 129, also on geological map.
C. H. Hitchcock : Geological map in Walling and Gray's Atlas of Massachusetts, 1871.
KHODE ISLAND GOAL MEASURES. 193
The extension along their sti-ikes of the several strata thus obscurely
exposed can not be traced with certainty more than a few rods. As in the
Mansfield area, there are no indications of the higher beds of the Carbonif-
erous section, so well exposed in the deep synclines of Dighton and Taun-
ton. The beds for the most part appear to belong to the few hiuidred feet
of Coal Measures coming in above the red Wamsutta series. Unless the
Carboniferous formation thinned out in this direction, the post-Carbonifer-
ous erosion of beds of this age alone in this field must be measured as
upward of 10,000 feet of strata.
ABINGTON QUADRANGLE.
In the southern part of this quadrangle more has not been possible
than roughly to discriminate the lower reddish strata of the Wamsutta
extension from the area occupied by the gray Carboniferous strata of the
Coal Measiu-es. The first-named series has already been described on
page 143.
There are about a dozen exposures of the gray series of the Coal
Measures known in this quadrangle. Beginning on the northwest, in
Abington, the gray series is seen in a small outcrop about 1^ miles south
from the granitite border. It is over 5 miles from this locality southward to
the outcrops including Sachems Rock near the Satucket River, in the town
of East Bridgewater.
Sachems Rock is a knob about 175 feet long and 20 feet high, composed
of massive-bedded, somewhat altered sandstone with bands of small pebbles
of white and smoky quartz, a fine-grained granitic rock, and a slate of
undetermined origin. The attitude of the beds is nearly horizontal, dipping,
if at all, to the north. There is a pronounced cleavage striking N. 77 °W.
The western side of the ledge has been opened for the jDurpose of quarry-
ing-. The smaller exposures to the east along the street are like the first,
showing to the eye abundant miniite scales of muscovite. The cleavage
planes maintain the same direction, and dip steeply to the north.
These beds are on the southern side of the broad, shallow syncline
which covers the southern part of the Dedham area, next north. They
would come, in accordance with the supposed structure, low down in the
Coal Measures.
In Hanover, half a mile east of Drinkwater River, and about 2,] 00
MON XXXIII 13
194 GEOLOGY OF THE iTAERAGANSETT BASIK
feet soutli of tlie northern border, is a probable outcrop of gray Carbonifer-
ous sandstone in tlie street; it may be a large bowlder. Bowlders of the
same lithological texture are abundant upon the surface. Southward to
the limits of the quadrangle no outcrops have been found.
Eastward, in tlie vicinity of Hanover Four Corners and near the east-
ern igneous border, several outcrops of the carbonaceous series appear.
Beginning on the northeast, in South Scituate on the east bank of Third
Hemng Brook there is either a large bowlder or an outcrop of sandstone
with bands of small pebbles. Southward, where the road from Hanover
Four Corners to North Pembroke crosses North River, there are good
exposures, forming a narrow defile through which the river escapes from a
broad valley on the west to the wide channel extending beyond this cut
to the sea. The strata are sandstone and arkose with coarse grits, bands
of slate, and carbonaceous matter, striking in an east-west direction and
standing at high angles. On the soutli side of the river, in August, 1889,
there was found in a coalj^ seam the stem of a calamite.
One and a half miles farther up the North River, where it is crossed
by the west road from the Corners to Pembroke, other exposures of the
Carboniferous conglomerates and sandstones occur, on the south side of the
stream. At the edge of the stream, in July, 1889, conglomerates and
sandstones were exposed under a mill. The bedding was much obscured
by joints. A few rods southward a blue compact sandstone is exposed, by
the roadside, apparently overlying the above-named beds. Across the road
and a few yards south of this cut a well was sunk, in July, 1889, through
10 feet of till into a dike of fine-grained, dark-colored diabase containing
numerous inclusions of granitic quartz from one-eighth to one-half inch
across, and a few pieces of feldspar. Angular fragments of red granitite
also occur in the diabase.
Half a mile farther up the river the stream lays bare a section of
closely jointed sandstones apparently dipping northward. In the bank
above the carriage road there is much carbonaceous waste. In the road
ascending the hill at the head of the westernmost of the thi-ee headwater
branches of Swamp Brook, in Pembroke, black clays occur, which are also
met with in excavations on the adjoining laud. The relations of these
deposits are very uncertain.
EHODE ISLAND COAL MEASURES. 195
TAUNTON QUADRANGLE.
The eastern part of the area designated the Taunton quadrangle is
nearly devoid of outcrops. In general it may be said that, except for a
triangular area on the southeast equal to about one-ninth of the whole, this
quadrangle is occupied by the rocks of the Carboniferous system. The strata
which, appear at the surface are mainly the harder conglomerates and sand-
stones, thrown into anticlines and synclines. Of these structures there are
at least two well-defined sets in the western part of the quadi-angle: the
Dighton syncline, with coarse conglomerates, coming to a nose-like end at
Dighton in Richmond Hill; and the Great Meadow Hill or Taunton syn-
cline, with the coarse conglomerates of the "Rocky Woods," west of
Taunton. Between these two great conglomerate areas lies the axis of an
anticline which probably traverses the area eastward to Middleboro. On
the northern side of the Rocky Woods tract is an anticlinal axis with nearly
vertical strata, north of which lies the Mansfield syncline.
The deposits so far recognized range from the highest beds in the for-
mation, including the Dighton conglomerates, downward toward the middle
of the Coal Measures section, including members of the Seekonk and Ten-
mile River beds. The precise position of the lowest strata seen is not defi-
nitely known. The following notes pertain to important natural exposm-es
of the strata and to artificial openings.
Red beds. — At one point in the northwestern part of the quadi-angle, about
1^ miles southeast of West Mansfield Station, in the road on the west side of
Hodges Brook, red slates are in contact with gray beds, striking N. 64° E.,
with nearly vertical dips. This is the only exposure of red beds known
in this area, but whether they are an extension of the red slates in Attle-
boro or are a reappearance of the Wamsutta group, there is no means of
deciding. The red slates in the drift south of this point afford plainly
marked flattened impressions of calamites.
Outcrops in Norton. — Midway betwceu Norton village and the southwestern
arm of the Norton reservoir is a low outcrop exposing about 100 feet of
conglomerates, sandstones, and slates. The strike here is nearly NE.-SW.
The conglomerate is composed of quartz, quartzite, and granitic pebbles
varying from half an inch to 3 or 4 inches in diameter. These beds can
be traced eastward for a quarter of a mile. Unless they are overturned
1 96 GEOLOGY OF THE NARRAGANSETT BASIX.
tliey overlie the following section, which is separated from them by several
hmidred feet of concealed beds.
Near the southeastern end of the Norton reservoir are broad exposures
of slaty arenaceous strata striking N. 54° E. and dipping 75° S. The fol-
lowing paced measurements give the succession, from south to north:
Section in Norton.
Feet.
1. Slate 3
2. Sandstone 39
3. Slate 5
4. Sandstone 2
5. Slate 12
6. Sandstone 8
7. Slate 1
8. Sandstone 27
9. Slate 9
10. Sandstone 18
11. Slate 48
12. Sandstone 22
13. Slate 2
14. Sandstone 34
The prevailing character of this section is similar to that of the beds
in the same anticlinal fold to the westward in Attleboro. The absence of
carbonaceous matter in the exposed sections is noteworthy.
A few isolated outcrops in the village of Norton display beds of con-
glomerate and grits, with variable dips. At one point the inclination is as
low as 50° N. The general structure of the belt of rocks through Norton
is probably anticlinal, for the Mansfield and Bridgewater synclinal trough
lies on the north and the Grreat Meadow Hill syncline is well marked on
the south.
winneconnet ledges. — Froui 2 to 3 mllcs uortheast of the exposures in
Norton occurs the Winneconnet section, on the east bank of Mulberry
Meadow Brook. There are here exposed upward of 200 feet of soft slaty
rock of an areiiaceoxis and often gritty texture. The cleavage dips west,
and its strike is N. 49° E., but the dip of the bedding is not easily deter-
mined. One and a half miles northwest of this locality is another exposure
of similar slates. In both places the surface of the rock weathers into
pear-shaped and rounded cavities, recalling the weathei'ing of the ottrelitic
RHODE ISLA:N^D GOAL MEASURES. 197
schists along the shores of Narragansett Bay. It is probable that the
metamorphism of the beds along this anticlinal line has been greater than
elsewhere in the eastern part of the basin, or that lower beds are here
exposed. (See fig. 6, p. 120, locality B.)
Eastward, outcrops appear in the vicinity of Scotland. About three-
fourths of a mile south of the town pebbly sandstones strike nearly E.-W.
and dip about 20° N., forming a low^ monoclinal ridge with an escarpment
facing the south.
Beginning the description on the western border of the quadrangle
again, the beds on the south side of this broad anticline are represented by
a few exposures. The best of these is at a point near the western margin,
on the west side of Chartley Brook, about 2 miles south of the Attleboro
branch of the Old Colony Railroad. An old quarry here occui-s in a knob
of the gray Carboniferous. The strike is N. 69° E., the dip 16° S., and
the following section is exposed from the top downward:
Section in Chartley quarry.
Feet.
Gray sandstone with small bauds of pebbles and flattened stems of plants, afford-
ing traces of coal 20
Black, compact, argillaceous beds, slightly micaceous, containing worm burrows of
a scolithoid habit; exposed 12
scoiithus beds. — The worm burrows referable to Scolithus at this locality
are somewhat sinuous or often recurved burrow^s filled with material similar
to the micaceous rock of the walls. The tubes vary from an inch to a
quarter of an inch in diameter. Where the wall has broken away from the
internal cast the surface is either smooth or rarely marked by minute cross
striations. The tubes are closely set, sonietimes apparently in contact.
The depth of the burrow exceeds in most cases 2 inches, and is probably
much deeper, but, on account of the interlacing of the tubes, this point can
not easily be ascertained. There seems no sufficient reason for giving a
specific name to these forms, since they have no importance in indicating
horizons even within the limits of this small basin.
One and a half miles east by north of this locality are outcrops of
compact argillite, succeeded on the south, near the head of Goose Brook,
by gritty sandstones containing distinct pebble bands, the dip of the last
being as steep as 80° S. These beds appear to be near the axial line of the
198 GEOLOGY OP THE NAERAGAifSETT BASm.
anticline which is traceable westward along- the valley of Tenmile River
in the Providence quadrangle.
Eastwardly there are no exposures along this strike line until we reach
the small quarry of gray sandstones opened alongside the railroad between
Britanniaville and the junction of the Attleboro branch railroad. About
li miles north-northeast outcrops occur on the west of Scudding Pond.
About 4J miles farther east coal has been reported on the southern border
of Gushee Pond, but the stratigraphy of this region is concealed by di'ift.
South of this belt, in the latitude of Taunton, the Seekonk beds, over-
lying the above, come in with southerly dips and disappear on the west
beneath the sjmchnal axis on which stands Great Meadow Hill. The strata
are medium conglomerates, sandstones, and shales. Coal has been found
in the uppermost beds underlying the coarse Dighton conglomerates about
1-^ miles northeast of Great Meadow Hill. So far as has been determined,
this is the highest occurrence of coal in the basin.
Taunton waterworks section. — Eastwardly aud at a somewliat lower level, though
probably in the horizon of the Seekonk beds, coal was again met with in
sinking an artesian well for the waterworks of the city of Taunton. The
well penetrated to a depth of 975 feet. The dip is reported to have been
about 40° N. The following table gives the thickness of the several strata
penetrated. The data were furnished by Mr. George F. Chace\ The
measurements are approximate, and are based upon the nature of the
materials brought up by the sand pump. The amounts indicate the depth
of each bed.
Record of artesian-ivell boring at Taunton.
Feet.
Superficial deposits (glacial drift) 85
Saudstoue 95
Coaly shales 20
Slate, blue 85
Sandstone 20
Conglomerate, quartzose 12
Sandstone 30
Slate, blue 81
Sandstone 22
Slate, blue 80
'Fourteenth Annual Report of the Water Commissioners of the City of Taunton [for 1889].
Taunton, 1890. Plate opposite p. 28.
EHODE ISLAND COAL MEASURES.
199
Becord of m'tesian-well boring at Taunton — Continued.
Feet.
Sautlstone and coaly slate
1 '\
Conglomerate, quartzose
Q7
Coaly shales
Slate, coaly, and sandstone 1^
5
' ' 13
7
Sandstone..
Coaly slate .
Sandstone.
Slate, blue ^^
Coaly slate .
Slate, blue .
Coaly slate
Slate, blue .
Coaly slate
Slate, blue .
10
5
5
10
15
3.3
40
Sandstone '^ '
Coaly shale - ■
Sandstone -"^
975
Depth of well
Tlie dip of the strata being, as stated, about 40° N., the actual thick
ness of the strata passed through woukl therefore amount to 639.6 feet.
westviiie section. — A partial section of these rocks occurs on the west bank
of Threemile River from Westviiie northward. The greater portion of
Fig. 28.— Geological section in Westviiie, Massachusetts, 1 mile west of Taunton. 5, coarse componnd conglomerate,
pebbles often a foot in diameter (Dighton group) ; 4, covered space, probably sandstones ; 3, fine conglomerate, quartzose
pebbles; 2, covered space, probably shales; 1, micaceous flaggy sandstones, much cleaved, and bearing casts and
impressions of calamites.
the section is drift covered, but enough is exposed to show the character of
these upper beds.
A similar section is repeated in most features 1 mile east of Taunton,
along the road from Taunton to East Taunton.
Westward along the Providence and Taunton turnpike, 2 miles east
of Great Meadow Hill, the sandstones and fine conglomerates underlying the
200 GEOLOGY OF THE NAREAGANSETT BASIN.
coarse conglomerates of the great syncline again appear in good exposures.
Annawon Rock (if it is not a bowlder) and the conglomerates, certainly in
place at this locality, come a little lower in this section.
Southward tliere are numerous outcrops of sandstone and conglomerate,
tintil at Swansea Factory the northern edge of the Dighton conglomerate
in the type syncline again comes in. The thick coating of di'ift makes a
correlation with the corresponding outcrops on the two sides of the anticline
which passes northeasterly across this field well-nigh impossible. East-
ward in J3ighton fine conglomerates come in below the coarse beds along
Muddy Cove Brook. Similar conglomerates crop out east of the Taunton
River, and again south of the syncline in Somerset.
The area southward to the Taunton River is occupied by sandstones
and shales, the latter appearing along the river shore.
Taunton River Valley. — As a marked cxcoption to the easterly strikes of the
beds in this field, an outcrop just east of Judson post-office, on the eastern
margin of the Taunton quadrangle, exhibits a north-south strike. This
outcrop marks the turn of the strata around the eastern end of the Taunton
syncline. The ridge, it is also worthj^ of note, is parallel to the course of
the Taunton River in this section.
The Taunton River exhibits a marked adjustment to the stratigraphy
of this portion of the field, although it is heavily masked by glacial drift.
The section of the river from Taunton eastward is along the strike of the
soft beds and across the strike of the hard beds. It is for this reason that
its east-west reaches are long, its north-south courses short. South of
Taunton the same adjustment is less perfectly exhibited. These facts
indicate a well-excavated preglacial channel.
MIDDLEBORO QUADRANGLE.
But few outcrops of the Carboniferous are exposed within the limits of
the Middleboro quadrangle, and it has not been possible to do more than to
indicate on the map the area occupied by the Carboniferous formation in
general without reference to horizons. The information gleaned from
bowlders, while it does not permit the delineation of the exact distribution
of strata, shows that this portion of the field is traversed by beds of con-
glomerate, sandstone, and slate resembling those of the Coal Measures,
and probably representing the lower portion of that series.
EHODE ISLAND COAL MEASURES. 201
South of Middleboro, on the west bank of the Namasket River, are
thi'ee low outcrops of gritty slate with thin layers of white quartz pebbles,
the size of the pebbles being not over an inch in diameter. Beds of this
character are probably not far above the base. It is interesting to note
again in connection with these beds the outcrop of granitite which occurs
immediately north in Namasket village.
At the southwestern border of Great Cedar Swamp, although there
are no outcrops, the abundance of slabby sandstones in the fences indicates
the probable eastward extension of the sandstones which occur near the
middle of the Coal Measures in the western part of the basin.
The area of felsites in Plympton has already been described (see
p. 116).
CHAPTER VI.
ORGANIC GEOLOGY.
In 1840, Dr. C. T. Jacksou stated, as a result of his survey of the Coal
Measures in Ehode Island, that, "from the fossil contents of the Carbonifer-
ous clay slate, we have reason to regard it as a fresh-water deposit, either
from lakes or from the estuary of some ancient river, whose waters may
have brought down from the lowlands on its banks an abundance of these
specimens of the ancient flora." ^ No observations of more recent date have
been published to overthrow Jackson's hypothesis of the uoumarine origin
of the sediments now preserved in the basin. Knowledge regarding the
fauna and flora has been gained slowly, and mainly through the work of a
few students resident in the Rhode Island part of the field.
Besides insects, the Pawtucket shales, according to Prof. A. S. Pack-
ard,^ have afforded "the impression of an annelid worm, several shells of
Spirorbis, and what appears to be the track of a gastropod mollusk."
IlSrSECT FAUNA.
Mr. Samuel H. Scudder has described and figured a small insect fauna
collected by various persons in the shales about the head of Narragansett
Bay. The following list is compiled from his paper. Insect Fauna of the
Rhode Island Coal Field :^
Insect Jawna about the head of Narragansett Bay.
Kame.
Based upon —
Locality.
Araclinida (spiders) :
Pawtucket, R. I.
Neuropteroidea :
(Not extant).
ton, R. I.
Orthopteroidea :
PalfeoblattarifB —
MylacridiB —
Mylacris packardii
AVing
Bristol and Pawtucket, R. I.
•Report on the Geology and Agriculture of Rhode Island, pp. 37-38.
-iAm. Jour. Sci., 3il series. Vol. XXXVII, 1889, p. 411.
3 Bull. U. S. Geol. Survey No. 101, 1893, 27 pp., 2 pis.
POSITION OF THE INSECT FAUNA.
Insect fauna ahoiii the head of Narragansett Bay — Continued.
203
Name.
Based upon— Locality.
Orthopteroidea — Continued :
Blattinari;e (cockroaches) —
Pawtucket? E.I.
Silver Spring, E. I.
Pawtucket, E. I.
E. Providence, E. I.
Cranston, E. I.
Pawtucket, E. I.
E. Providence, E. I. (Drift.)
Pawtucket, E. I.
Pawtucket, E. I.
Silver Spring, E. I.
Silver Spring, E. I.
SP
Fore wing
Fore wing
Hind wing
gorhami
Fore wing
Protophasmida (leaf and stick insects) :
STRATIGRAPHIC POSITION OF THE FAUNA.
The discoverers of this interesting insect fauna appear to have done
little toward establishing the horizon or horizons in whicli it occurs, if it
has any assignable limits. The specimen of Etoblattina from Fenner's
ledge in Cranston, so Mr. Scudder quotes, was found "near the extreme
western upturned edge of the Carboniferous in the plumbago mining district,
and [is] therefore probably older than the others." ^
The localities which have so far furnished these insect remains are
traversed by strata relatively low down in the Coal Measures section.
The outcrops in East Providence are in the horizon of the Tenmile
River beds. The shales of the Cranston series lying to the west of these
exposures are probably in part still lower in the section, extending down-
ward nearly to the base of the Carboniferous. It would appear, therefore,
that, so far as at present known, this fauna ranges from near the base of
the Coal Measures to and into the Tenmile River beds. The higher strata,
which have a nearly equal thickness, have not afforded fossils. The locality
at Bristol is somewhat in doubt as to its place in the section.
ODONTOPTERIS FliORA.
The flora of the Rhode Island Coal Measures, according to the list of
plants collected by the Rev. E. F. Clark and identified by the late Leo
'Op. cit., p. IG.
204
GEOLOGY OF THE NAERAGANSETT BASIN.
Lesquereux, is peculiarly rich in species of Odontopteris. As yet the upper
portion of the Coal Measures, from near the base of the Dighton group
upward in the northern field, has afforded little or no evidence. From the
list of localities which appear to have been visited in collecting the fossils
in Lesquereux's list it is possible to draw conclusions of some value regard-
ing the flora so far as it is known.
The localities, so far as the Providence quadrangle is concerned, are
practically limited to the exposures which occur in the lower half of the
series of sandstones and shales of the Coal Measures, or to essentially the
same range as the insect fauna. Lesquereux^ concluded from these plants
that the Rhode Island Coal Measures were equivalent to the beds of the
upper Carboniferous in Pennsylvania. Until the flora of the uppermost
members of the period in this basin is known nothing further can be said
regarding their Permian affinities. (See also pp. 170, 181,)
List of plants identified hy Leo Lesquereux.-
Species
Locality.
Pawtucket.
Valley Falls.
Pawtucket.
Pawtncket.
Pawtucket.
Pawtucket.
Pawtucket.
Pawtucket.
Valley Falls.
Valley Falls.
Valley Falls.
Pawtucket.
Pawtucket.
Pawtucket.
Pawtucket.
Pawtucket.
Pawtucket.
Pawtucket.
Pawtucket.
Pawtucket.
Pawtucket.
Bristol.
Pawtucket.
Pawtucket.
Pawtncket.
?
9. Neuropteris deoipiens
10. Goniopteris (Pecopteris) unita
14. Sckizopteris (Rhacophyllum) trichomanoidos
15. Oligocarpia gutbieri
19. niiltoni (same as 13)
22. Pseudopecopteris diuiorpha
24. Parallel narrow rachises of piunie of No. 7, mostlj'
!Am. Jour. Sci., 3d series, Vol. XXXVII, 1889, p. 411.
= Ibid., p. 229.
OCCURRENCES OF COAL. 205
A more complete list of plants found in the Rliode Island Coal Meas-
ures has been compiled by the Franklin Society of Providence, and
published in its Report on the Geology of Rhode Island, 1887.
COAL BEDS.
The following- account of the coal beds in the basin, written by Edward
Hitchcock, who descended into all the accessible mines, sets forth the
condition of things as late as 1853, since which time few mines have been
opened:
1. Beds of coal in Mansfield. — These have been opened iu two parts of the town.
One is near the center, where a shaft was sunk by the Mansfield Coal Company, some
fifteen years ago, 64 feet, but only a little coal was found.
About the same time the Mansfield Mining Company sunk a shaft 84 feet near
the Hardon farm, 2 miles southwest of the center. A drift was then carried across
the strata, and it is said that seven beds, of various thickness up to 10 feet, were
found. Dip of these beds, 53° NW. Strike, SW. and NE.
More recently, in 1848, I believe, the Mansfield Coal and Mining Company,
through the enterprise and perseverance of B. F. Sawyer, esq., sunk a shaft near the
same place, 170 feet and 10 feet in diameter, from which, according to the statements
of Thomas S. Eidgway, esq., the engineer, they have carried a south tunnel 6C0 feet,
aud other tunnels and gangways to about the same amount. Not less than thirteen
beds of coal have been crossed, but none of them thick. They are very irregular,
sometimes swelling out to 6 or 8 feet in thickness, and then pinched up to a few inches.
The dip varies from 30° to 70° NW., and the strike is nearly NE. and SW. Although
these excavations are not far from the old Hardon mine, the beds are said to have
little correspondence.
2. Bed in Foxiorough. — This is only about 2 miles from the Mansfield beds, and
two excavations were made there several years ago, and good coal obtained, but the
pits were filled up so that I could not ascertain the strike, dip, aud width of the bed.
3. Beds in Wrentham. — In the south part of the town a i)it was sunk many years
ago, about 170 feet, mostly in dark carbonaceous slate, aud several beds found. The
coal which I have seen from this spot is not good, having 40 per cent of ash. Strike
of the bed, nearly E. and W. ; dip, 45° N.
i. In Baynham. — An outcro]) of coal appears in this town, about 3 feet thick,
which has not been explored, except a few feet. Strike, N. 50° E.; dip, 45° SE.
5. In Bridgeicater. — Indications of coal were shown me from the rock thrown up
in digging a well in the south part of the town, but nothing further could be learned.
6. In Taunton. — Two miles northwest of the town, a similar opening was shown
me, but I could not learn the dip and direction of the slate. Four miles to the west
of the town, I was told, similar indications exist. The same is true of West Bridge-
water, and in Berkeley coal plants are found, such as usually accompany beds of
coal.
206 GEOLOGY OF THE NAEEAGANSETT BASIN.
7. In Gumberland, Rhode Island. — This is called the Roger Williams miue, whicli
was opened many years ago; but the works were burnt, and the explorations aban-
doned, but they have been resumed within a few years under the superintendence of
Capt. Thomas Martin. A shaft has been suuk 300 feet perpendicularly, into which I
descended with Captain Martin. The old bed, whose strike was nearly NE. and SW.,
has been abandoned, and by carrying a horizontal shaft 260 feet a new bed was
struck, which, at the place, runs nearly IST. and S. and dips west about 45°. The
average width was stated to be 15 feet, and in some places 23 feet. If this be not a
mere protuberant mass, occasioned by lateral pressure, it indicates a larger amount of
coal than I have seen in any other mines in this coal field.
8. The Valley Falls mine. — This is scarcely more than a mile south from the
Eoger Williams mine, yet the strike of the beds will not allow us to suppose them
connected. The operations here are carried on by the Blackstone Coal Company. A
shaft is carried down, which follows a bed of coal, with a dip near the surface of 30° to
45°. This bed, whicli I examined several years ago, to a depth of about 50 feet, exposed
a thickness of coal from 6 to 9 feet, and the direction was IST. 50° to 60° E. Since that
time the "incline," as the miners call it, has been j)ushed downward 500 feet, or
about 375 feet of perpendicular depth, and, as already mentioned, the strata have
been found to curve very much, and not less than five beds of coal have been crossed,
the best having a width of 6 feet. One nest of coal was found 30 feet square.
9. In Seekonk. — I am informed by J. IST. Bolles, esq., of Providence, that the out-
crop of a bed of coal was found in digging a well in this place, only 15 feet from the
surface. Its quality was similar to that found at Valley Falls. In the same region
occur very fine specimens of coal plants, especially calamites.
10. In Providence. — The same gentleman, in boring for water in the north part
of Providence, at the depth of 60 feet, struck a bed of coal dipping NB. 45°, which
is 10 feet thick, and of the same general character as that at Valley Palls, which is
known to burn well.
11. In Cranston, Rhode Island. — This town is on the west side of Narragansett
Bay, along which the coal rocks extend as far as Wickford. In Cranston, according
to Dr. C. T. Jackson, "slate, graphite, and impure anthracite" are found in an excava-
tion 7 or 8 feet deep. Coal plants are very abundant on Warwick Neck, but no coal
has been found.
12. In Bristol, Rhode Island. — The coal bed in this place is in the west part of the
town, and the spot where it crops out is only a few feet above the harbor. It was
discovered in sinking a large well. Although I descended into it, I could not ascertain
the thickness of the bed, nor with accuracy its strike and dip. Approximately it runs
N. a few degrees E., and dips westerly about 48°. The coal did not appear to me to
be as much crushed as in some mines, and seems of an excellent quality.
13. Portsmouth mine, or Case's mine, in Rhode Island. — This mine, situated in the
northeast part of the island of Rhode Island, was opened in 1808, which was earlier
than the Pennsylvania mines were explored. At that time the mode of burning
anthracite was not known, and the coal was not sought after, and the work was
OCCUERENCES OF COAL. 207
abandoned iu 1813 or 1814. Some years afterwards it was resumed, and in 1827,
according to Mr. Clowes, the agent, 20 men and 5 boys raised about 1,100 tons of
coal, coarse and fine. But the work was again abandoned not long after, and not
resumed till ISIT, when the mine was opened by the Portsmouth Coal Company, which
has also ceased operations there. Mr. Barbour speaks of the amount of coal and
rock, "principally the former," that has been excavated at this place, as about
100,000 tons.
Three beds were discovered at this place, "all of workable width." Dr. C. T.
Jackson says that the bed last wrought was 13 feet thick. He states its strike to be
S. 80° W. and IST. 80° E. ; dip, 35° southeasterly. Mr. Clowes, however, says that the
beds run NE. and SW. and dip from 40° to 90° southeast. As the mine is now
unwrought, I could not settle these points.
14. The Aquidneclc mine. — [In the account of this mine it is stated that three
beds of coal occur, only one of which, from 2 to 20 feet thick, was worked by the
Aquidneck Coal Company. The middle bed was followed down to the depth of 020
feet, from which six gangways were extended, from 80 to 844 feet each. During the
last half of 1851, 3,100 tons of coal were taken out, and an opening made into a sub-
jacent bed. — J. B. W.J
15. In Neioport^ Rhode Island. — [An outcrop of coal in the southeast part of the
town is described, and it is stated that during the Eevolutionary war the British
made excavations at this spot in search of fuel. The prospect is poor. The shale
abounds in coal plants. — Abstract by J. B. W.] '
Otlier references to coal will be found on pages 169, 182, 189, 190, 198.
SEARCH FOR COAL.
As the coal beds in this basin are mainly concealed in depressions
filled with drift, or have their outcrop under river beds and swamps, the
details of this report are mainly useful when made the basis of a process of
exclusion, in which the prospector searches along lines of strike between
bands of strata which are shown to be barren. So far as can be ascer-
tained from field evidence, coal beds are likely to be found in the greater
part of the field outside of the red rocks and lenticular areas occupied by
the upper conglomerates, which together do not occupy an area greater
than 3U square miles. In most of the area thus left, the dip of the beds is
low, so that experimental borings are likely to penetrate several strata.
Where the strata stand at a high angle the chance of meeting with coal
beds is less good, although they may exist at one side of the trial boring in
the same field. Such a belt of highly inclined strata runs north-northeast
' Mass. House Documents No. 39, March, 1853, pp. 9-13.
208
GEOLOGY OF THE NAREAGAI^TSETT BASIK
across tlie northwestern part of the Taunton quadrangle, through Norton,
in the vicinity of Providence, and along the lower course of the Warren
Fig. 29.— Case where a boriuK w ilie iiio.st economical and certain metliod ol detonuiuiug the presence of a series of
coal beds in a given thickness of coal measures.
River in Swansea. In areas of vertical strata, trenching across the upturned
edges of the beds would better serve the purpose. (See figs. 29 and 30.)
THICKTSESS OF THE CARBONIFEROUS.
There are but few cross sections of the strata obtainable in the Narra-
gansett Basin which are so far free from the perplexing hindrances set forth
in the introduction to this report that the geologist can with confidence
Fig. 30 Case where a boring may miss an important coal bed and is not likely to discover more than one, and
w here a trench at right angles to the strike would reveal the true number of seams of coal.
give an estimate of the thickness of the beds entering into them. The
most satisfactory line of section in the northern part of the basin passes
from the southern margin through the Dighton-Swansea and Great Meadow
Hill or Taunton synchnes toward Mansfield and the northern border. The
general relations of the structure along this line are shown in fig. 8 (p. 122).
Measurements along this line give about 12,000 feet as the thickness of the
THICKNESS OF THE GARBONIPEEOUS. 209
strata between the granitic base and the top of the Dighton group. The
evidence on which this estimate is based is as follows :
From the south bank of the Taunton River north of Steep Brook to
the axis of the Dighton-Swansea syncline there is a section from the base
to the uppermost beds of the series. The distance along this line perpen-
dicular to the strike is approximately 3 miles, and the dip of the beds is
generally steep; it may be assumed to be as high as 45". This gives 11,198
feet as the thickness of the strata remaining along this margin of the basin.
Between the axes of the Dighton-Swansea and the Taunton synclines
is a distance of 6 miles. The intervening beds, in anticlinal position,
though very imperfectly exposed, nowhere exhibit in the few exposures
available for interpretation foldings or thrusts likely to diminish or increase
the estimate of thickness based on measurements across the interval between
the two synclinal axes. The dips on the southern side of the anticlinal
axes are very steep, mainly above 45°; the dips on the northern side are
much less steep, mainly below 45°. The lowest beds exposed anywhere
along the anticlinal axis lie above the basal beds of the Carboniferous;
so that estimates along this line must necessarily fall short of the base.
Assuming 45° as the avei'age dip over this anticlinal section, and since the
beds over half the distance between the adjacent synclines have 3 miles of
outcrop as before, we obtain the same amount as on the southern side of the
Dighton-Swansea syncline. Inasmuch as this estimate of about 11,200
feet is a minimum and does not reach the base, it is probable that the beds
increase in thickness toward the middle and now deeper part of the basin.
Northward from the Taunton syncline to the northern border near
Mansfield there is certainly one anticlinal area, and another syncline in
the Mansfield coal basin ; but there are no exposures of the upper conglom-
erate series along this line, and the outcrops are totally inadequate for
making even minimum estimates of thickness.
West of the line of section above described an aj^proximate estimate
of thickness can be founded upon the strata exposed between the western
end of the Taunton syncline in Seekonk and the axis of the Attleboro syn-
cline. From the Perrin's anticline, where there is a probable overthrust of
the beds on the south, to the axis of the adjacent Attleboro syncline there
is a fairly continuous exposure of outcrops, ranging in inclination from 45°,
for a few hundred feet on the south, to nearly vertical for most of the
MON xxxiii 14
210 GEOLOGY OF THE NAERAGANSETT BASIN.
remaining distance to tlie Attleboro synclinal axis. Assuming 75° as the
average dip across these upturned beds, which have a breadth of outcrop of
about 11,900 feet, -we obtain about 11,500 as a measurement of the thick-
ness. Again this is a minimum estimate, reaching only from the top of the
highest remaining beds in the synclinal trough to the lowest exposures in
a broken anticlinal arch.
These measurements, taken in the northern part of the basin, across
comparatively simple great folds, enforce the conviction that the strata now
remaining in the deeper, central portion of this basin can not be less than
12,000 feet in thickness. This estimate agrees closely with that given for
the Carboniferous strata of the Joggins section in Nova Scotia, which are
about 13,000 feet thick.
U.S. GEOLOGICAL SURVEY
MONOGRAPH XXXIll, PL. XVII
GEOLOGICAL M/\P OF THE NORTHEM AND EASTERN PORTIONS OF THE NARRAGM^SETT BASIN
llY.I.Ti.WOODWdKTH, ASSISTANT (H'JJLOOIST. M.S. SHALKH.GKdl.dClsl' IX I IIAIKiK
Scale
LEGEND
SEDIMENTARY ROCKS
^ s
IGNEOUS ROCKS
^^\
Diabase dikes
Quartz-porpMn
Fa nils
OUTCROPS
ACKNOWLEDGMENTS.
I wish to express my indebtedness to my associates in this work for
much guidance and aid, both in the field and in the hiboratory, and particu-
larly to Dr. Foerste for many suggestions and actual aid in delimiting
the Cambrian, Carboniferous, and igneous rocks about North Attleboro.
The follo^ying-named gentlemen rendered assistance at one time or another
during the course of the field work: C. W. Coman, U. S. G. S.; Robert
Wainwright, W. E. Parsons, Harry Landes, U. S. G. S.; J. Ralph Finlay,
U. S. G. S., and G. W. Tower. To Prof J. E. Wolff my thanks are due
for examining many thin sections of rocks. To Prof George H. Barton I
am indebted for the privilege of reading a manuscript report, with sections,
based upon his study of the Norfolk County Basin, and to Prof A. S.
Packard, of Brown University, for the use of the collection of plants from
Rhode Island. All the photographs illustrating this monograph were taken
under my immediate supervision by Mr. Philip P. Sharpies, of Cambridge,
Massachusetts.
APPENDIX.
BIBLIOGRAPHY OF THE CAMBRIAN AND CARBONIFEROUS ROCKS OF
THE NARRAGANSETT BASIN.
Barton, George H. Geology of the Norfolk County Basia. Manuscript thesis
Massachusetts Institute of Technology, Boston, Massachusetts, 1880, 63 pp.
and Crosby, W. O. See Crosby, W. O.
Battey, T. J. See Providence Franklin Society.
Beche, de la, H. A geological manual, Philadelphia, 1832, pp. 401, 404.
Blake, W. P. The plasticity of pebbles and rocks. Proc. Am. Acad. Arts Sci., vol.
18, 1869, pp. 199-205.
Clark, Edgar P. Studies in the Rhode Island Coal Measures. Proc. Newport ISTat.
Hist. Soc, Vol. II, 1883-84, pp. 9-12.
Collie, Geo. L. The geology of Conanicut Island, E. I. Trans. Wisconsin Acad. Sci.,
Vol. X, 1894-95, pp. 199-230; map, pi. iv.
Cozzens, Issachar. A geological histoiy of Manhattan or New York Island, New
York, 1843, pp. 60-64, pi. vi.
Crosby, W. O. Contributions to geology of eastern Massachusetts, 1880.
and Barton, G. H. Extension of the Carboniferous formation in Massachusetts.
Am. Jour. Sci., 3d series, Vol. XX, 1880, pp. 416-420.
On the great dikes at Paradise near Newport. Proc. Boston Soc. Nat. Hist.,
Vol. XXIII [1886], pp. 325-330.
Dale, T. Nelson. A contribution to the geology of Ehode Island. Proc. Boston Soc.
Nat. Hist., Vol. XXII, 1883, pp. 179-201 pis. i-iii. Partial bibliography given,
pp. 180-182. Also the geology of the tract known as Paradise, near Newport.
Proc. Newport Nat. Hist. Soc, 1883-84, Doc. 2, pp. 3-5, 2 pis.
Eemarks on some of the evidences of geological disturbance in the vicinity of
Newport. Proc. Newport Nat. Hist. Soc, 1883-84, Doc. 2, pp. 5-8.
The geology of the mouth of Narragansett Bay. Proc. Newport Nat. Hist. Soc,
1884-85, Doc. 3, May, 1885, pp. 5-14.
On metamorphism in the Ehode Island coal basin. Proc. Newport Nat. Hist.
Soc, 1884-85, Doc. 3, 1885, pp. 84-86.
A contribution to the geology of Ehode Island. Am. Jour. Sci., 3d series. Vol.
XXVII, 1884, pp. 217-228, 282-291. Also Proc. Canadian Inst., 1884-85, p. 21.
List of minerals and rocks occurring in the vicinity of Newport. Proc. Newport
Nat. Hist. Soc, 1886-87, Doc. 5, pp. 29-31.
Dana, J. D. Manual of geology, 3d edition, 1880, pp. 314-315.
Manual of geology, 4th edition, 1895, p. 657.
Archean axes of eastern North America. Am. Jour. Sci., 3d series, Vol. XXXIX,
1890, pp. 378-388. P. 380.
212
BIBLIOGEAPHY. 213
Davis, W. M. The physical geography of southeru Xew Eu gland. Nat. Geog. Mono-
graphs, I, 1895, No. 9, 36 pp.
See Shaler, N. S.
Day, S. Anthracite in Wreutham, Mass. Am. Jour. Sci., 3d series, Vol. XXIII,
1833, p. 405.
De la Beche. See Beche, de la, H.
Dodge, W. W. Xotes on the geology of eastern Massachusetts. Proc. Boston Soc,
Nat. Hist., Vol. XVII, 1875, pp. 388-419.
Eaton, Amos. Argillite embracing anthracite coal. Am. Jour. Sci., 1st series, Vol,
XVI, 1829, pp. 299-301.
Emmons, A. B. Notes on the Rhode Island and Massachusetts coals. Trans. Am.
Min. Eng., Vol. XIII, 1885, pp, 510-517.
Foerste, Aug. F. The igneous and metamorphic rocks of the Narragansett Basin.
Manuscript thesis deposited in the library of Harvard University, 1890.
■ See Shaler, N. S,
Haldeman, S. S. See Taylor, E. G.
Hitchcock, C. H. Geology of the island of Aquidneck. Proc. Am. Ass. Adv. Sci.,
Vol. XIV, 1860, pp. 121-137.
Synchronism of the coal beds in New England and in the western United States.
Proc. Am. Ass. Adv. Sci., Vol. XIV, 1860, pp. 138-143.
The distortion and metamorphism of pebbles in conglomerates. Proc. Am. Ass.
Adv. Sci., Vol. XVI, 1867, pp. 124-127.
Geological map of Massachusetts. Walling and Gray's Atlas of Massachusetts,
1871, 20 pp.
Hitchcock, Edward. Eeport on the geology of Massachusetts, 1833.
Final report on the geology of Massachusetts, 1841, 831 pp.
Eeport to the governor of Massachusetts on certain points in the geology of
Massachusetts, with a map of the Bristol and Ehode Island coal field. Mass.
House Doc. No. 39, 1853.
The coal field of Bristol County and Ehode Island. Am. Jour. Sci., 2d series.
Vol. XVI, 1853, pp. 327-336.
HoUey, A. L. Notes on the iron ore and anthracite coal of Ehode Island and Massa-
chusetts. Trans. Am. Inst. Min. Eng., Vol. VI, 1877, pp. 224-227.
Jackson, C. T. Geology and agriculture of Ehode Island, 1840.
Lesquereux, Leo. Description of the coal flora of the Carboniferous formation in
Pennsylvania and throughout the United States. Second Geol. survey of Penn.,
Eeport of Progress, P, Vol. Ill, 1884, pp. 867-868.
The Carboniferous flora of Ehode Island. Am. Naturalist, Vol. XVIII, 1884,
pp. 921-923.
Lyman, B. S. Against the supposed former plasticity of the puddingstone pebbles
of Purgatory, E. I. Proc. Am. Assoc. Adv. Sci., Vol. XV, 1867, p. 83.
Maclure, Wm. Observations on the geology of the United States, 1817, map. '
Marcou, Jules. Lower and Middle Taconic. Am. Geologist, Vol. VI, 1890, pp. 97-98.
Pirsson, L. V. On the geology and petrography of Conanicut Island, E. I. Am.
Jour. Sci., 3d series. Vol. XLVI, 1893, pp. 363-378.
Providence Franklin Society. Eeport on the geology of Ehode Island, Providence,
1887, pp. 130. Addenda, 1888, pp. 131-132. Gives numerous references to local
newspaper accounts.
214 GEOLOGY OF THE Is^AERAGAlsrSETT BASIN.
Rogers, W. B. [Elongation of pebbles in conglomerate at Purgatory, near Newport,
K. I., and elsewhere.] Proc. Boston Soc. Nat. Hist., Vol. VII, 1860, pp. 391-394.
[Shells in siliceous slate pebbles in the drift at Fall Kiver, etc.] Proc. Boston
Soc. Nat. Hist., Vol. VII, 1860, pp. 389-391.
On the Newport conglomerate. Proc. Boston Soc. Nat. Hist., Vol. XVIII, 1875,
pp. 97-101.
Salisbury, Charles M. See Providence Franklin Society.
Shaler, N. S. On the geology of the island of Aquidneck and the neighboring shores
of Narragansett Bay. Am. Naturalist, Vol. VI, 1872, pp. 518-528; 611-621;
751-760.
Note on the geological relations of the Boston and Narragansett bays. Proc.
Boston Soc. Nat. Hist., Vol. XVII, 1875, pp. 188-490.
On the geology of the Cambrian district of Bristol County, Mass. Bull. Mus.
Comp. Zool. Harvard Coll., Vol. XVI, No. 2, 1888, pp. 13-20, map.
and Foerste, A. F. Preliminary description of North Attleborough fossils.
Bull. Mus. Comp. Zool. Harvard Coll., Vol. XVI, No. 2, 1888, pp. 27-41, 2 pis.
Shurrocks, T. H. See Providence Franklin Society.
Taylor, E. C, and Haldeman, S. S. Statistics of coal, etc., 2d ed., Philadelphia,
1854, p]). 446-456.
Teschemacher, J. E. On the fossil vegetation of America. Boston Jour. Nat. Hist.,
Vol. V, 1846, pp. 370-385.
Vanuxem, L. Experiments in anthracite, plumbago, etc. Am. Jour. Sci., 1st series.
Vol. X, 1826, pp. 104-105.
Wadsworth, M. E, A microscopical study of the iron ore, or peridotite, of Iron
Mine Hill, Cumberland, li. I. Bull. Mus. Comp. Zool. Harvard Coll., Vol.
VII, 1881, No. 4, pp. 183-187.
Walcott, C. I). Position of the Olenellus fauna. Am. Jour. Sci., 3d series. Vol.
XXXVII, 1889, pp. 387-388.
The Olenellus fauna. Tenth Ann. Kept. U. S. Geol. Survey, Part I, 1890, p. 567.
Note on the brachiopod fauna of the quartzitic pebbles of the Carboniferous con-
glomerates of the Narragansett Basin, Rhode Island. Am. -Jour. Sci., 4th series.
Vol. VI, 1898, pp. 327-328.
Ward, L. F. Distribution of fossil plants. Eighth Ann. Bept. F. S. Geol. Survey,
Part II, 1889, p. 853.
Wood-worth, J. B. Carboniferous fossils in the Norfolk County Basin. Am. Jour.
Sci., 3d series, Vol. XLVIII, 1894, pp. 145-148.
GEOLOGY OF THE NARRAGANSETT BASIN
Part III.— THE CARBONIFEROUS STRATA OF THE
SOUTHVi/ESTERN PORTION OF THE BASIN
WITH
AN ACCOUNT OF THE CAMBRIAN DEPOSITS
By A.XJC-. F. FOERSTE
CONTENTS.
Page.
Chaptek I. — Introduction 223
Difficulties of the field 223
Arraugemeut of report 225
Chapter II. — The western islands of the hay 227
Dutch Island 227
Conanicut Island 228
Fox Hill, Beaver Head 228
Northern half of the island, north of Round Swamp 229
Southern half of the island, south of Round Swamp 23£
Shale region 232
Granite area, the Dumplings, and arkose region west of the Dumplings 233
Hope Island 235
Prudence Island 237
Chapter III. — The western shore of the bay 242
From Sauuderstown to Narragansett Pier 242
Along the shore 242
West of the cove and Pattaquamscott River 246
From Saunderstown to Wickford 248
From Wickford to East Greenwich 251
Western border of the Carboniferous basin, from East Greenwich to Natick and north-
ward into Cranston 252
Rocks east of the western border of the Carboniferous area in Warwick and southern
Cranston 256
Warwick Neck 258
Chapter IV. — The northern shore of the bay 259
Providence River and eastward 259
Rumstick Neck 260
Popasquash Neck 261
Bristol Neck 261
Carboniferous area 261
Granite area 262
AVarreu Neck 264
Conglomerates and shales of Swansea and Warren, north of the necks 264
Gardeners Neck 267
Braytons Point and northward 268
Se wammock Neck 268
Chapter V. — The eastern shore of the bay 269
Steep Brook 269
Fall River 270
Townsend Hill 270
Tiverton 271
Gould Island 272
Granite area at the northeast eud of Aquidneck Island... 273
Eastern border of the Carboniferous basin south of Tiverton Four Corners 274
Sandstone series between Windmill Hill and the cove north of Browns Point 275
217
218 CONTENTS,
Chapter V. — The eastern shore of the bay — Continued. Page.
Coarse conglomerate series along the east, shore of Sakonnet River 278
High Hill Point 278
Fogiand Point 278
Exposures west of Nonquit Pond . .-. 279
Exposures between Tiverton Four Corners and the northeast side of Nanniiquacket
Pond 280
Little Compton shales - 281
Chapter VI. — Aquidneek, or the Island of Rhode Island, with the islands of Newport Harbor. . 284
Arkose and pre-Carboniferous rooks on Sachuest Neck 28i
Arkose 284
Pre-Carboniferous rocks 286
Eastern shore of A(iuidueck Islaud as far south as the second cove northvrest of Black
Poiut -..- 288
Coarse conglomerates and underlying sandstone series from Black Point to the north end
of Smiths Beach ---- 290
Coarse conglomerates and underlying rocks on the neck at Eastons Point 294
Paradise coarse conglomerates - 295
Paradise rocks 295
The Hanging Rocks 298
Pre-Carboniferous area - 300
Isolated conglomerate exposures near Eastons Pond and northward 303
Miantonomy Hill and Coasters Harbor Island conglomerates 304
Miantonomy Hill 304
Beacon Hill 304
Field exposures of coarse conglomerates 304
Coddington Neck 305
Bishop Rock 305
Coasters Harbor Island
Newport Harbor Islands 307
Gull Rocks -- 307
Rose Island 308
Conanicut Island - 308
Line of separation between Carboniferous and pre-Carboniferous rocks 308
Goat Island and Little Lime Rock 309
Fort Greene 309
Morton Park and southward 309
Northeast lines of possible faulting 310
Carboniferous rocks along the Newport Cliffs 310
Newport Neck and southern cliff rocks 314
Greenish igneous rock in the cliffs southwest of Sheep Point 314
Granite area at the south end of the cliffs 315
Granite area on eastern Newport Neck 316
Greenish and purplish argillitic rock of middle Newport Neck 316
Pre-Carboniferous green and purple shales of western Newport Neck 316
Shale series from Coddington Cove to Lawtons Valley 319
Greenish-blue shales of Slate Hill and southward 320
Shale series north of Lawtons Valley 320
Shore exposures north of Coggoshall Point 320
Portsmouth mine and northeastward 321
Line of exposures three-eighths of a mile west of the Newport road 326
Shale series at Butts Hill 327
Green shales and conglomerates of the northern syncline 327
Green shales along the western Newport road 327
Portsmouth conglomerates 328
Relations to Slate Hill shales 329
CONTENTS. 219
Chapter VII. — The Kingstowu series 331
Unity and Hthological character of the Kingstown sandstone series 331
Section from the Bonnet to Boston Neck 333
Section from the Bonnet to Hazard's quarry and Indian Corner 333
Kingstown series in southwestern Cranston and western Warwick 334
Probable thickness of the Kingstown sandstone series in Cranston and Warwick. .. 336
AVarwick Neck exposures 386
Exposures on the western islands of the bay 337
Thickness of strata between the Bonnet and Dutch Island 337
Lithology of the Dutch Island series 338
Beaver Head section 338
Total thickness of Kingstown series, including the conglomerate at Beaver Head.. 338
Western shore of Conanicut 339
Eastern shore of Conanicut 339
Probable folding in the northern part of Conanicut Island 340
Hope Island 341
Kingstown series exposures on the western islands 342
Prudence Island 342
Western Bristol Neck 343
Eumstick Neck 344
Kingstown sandstones equivalent to lower part of Coal Measures group 344
Triangular area of the Kingstown series in the Narragansett Basin, narrowing
southward 344
Thickness of the series and evidence of folding 345
Rocky Point conglomerate and its connection with the estimate of the thickness of
the northern section 346
Chief features of the Kingstown series 346
Fossil-plant localities 347
Chapter VIII. — The Aquidneck shales 348
Area occupied by the Aquidneck shale series 348
Southern Conanicut 349
Prudence Island 350
Thickness of shale series on each side of Prudence Island syncliue 351
Bristol Neck 351
Aquidneck Island 352
Thickness of the shale section east of the Portsmouth syncline 353
Probable thickness of the shale section west of the Portsmouth syncline 353
Lithological variations in the shale series 354
Geological structure of the middle third of Aquidneck Island 354
Strata probably folded 355
Gould Island of the Middle Passage 356
. Southern third of Aquidneck Island 356
Upper green shales of the Aquidneck series 356
Sakonnet sandstones of the Aquidneck series west of the river 357
Thickness of the upper green shales 357
Thickness of the Sakonnet sandstones 358
Northern extension of the Aquidneck shales 358
Equivalents of Kingstown sandstone and Aquidneck shale series northeast of Warren Neck. 358
Sakonnet sandstones on the oast side of the river 359
Absence of the shale series beneath the coarse conglomerates east of the Sakonnet River . .. 360
AVedge-shaped areal distribution of the Aquidneck shale series 361
Equivalence of the Kingstown sandstones and the Aquidneck shales 361
Fossils of the Aquidneck shale series 363
220 CONTENTS.
Paffe.
Chaptee IX.— The Purgatory conglomerate 364
Coarse conglomerate overlying the Aquidneck shale series 364
Sakonnet sandstones within the Aquidneck shales, in transition to the coarse con-
glomerate 365
Coarse conglomerate forming the latest Carboniferous rocks in the southern part
of the Narragansett Basin 365
Purgatory conglomerate as a typical exposure 365
Identity of the Purgatory and Sakonnet River western shore coarse conglomerate. .. 366
Possible syncline between the two western Paradise ridges of conglomerate 366
Hanging Eock ridge possibly the eastern side of an anticlinal fold 367
Dips immediately east of Hanging Rock ridge 367
Interpretation adopted 367
Southward pitch of the great Paradise-Hanging Rock syncline 368
Southward pitch of the Sakonnet River syncline 369
Western coarse conglomerate exposures 369
Possible syncline immediately west of Miantonomy Hill 369
Possibility of two horizons of conglomerate at Miantonomy Hill 370
Interpretation adopted 371
Geological position of the Newport Cliff section 371
Portsmouth synclinal conglomerate 373
Conglomerates of Warwick Neck and Swansea 373
Thickness of the coarse conglomerate 373
Fossil localities 374
Chapter X. — The arkoses and basal conglomerates 375
Natick arkose 375
From Natick to Cranston 375
Base of the Carboniferous south of Natick 376
Probable relations between the various granites and pegmatites and the Carbon-
iferous beds 376
Tiverton arkose 378
From Steep Brook to Nannaquacket Pond 378
South of Nannaquacket Pond 379
Equivalence Of the Tiverton arkoses to those near Natick 379
Sachuest arkose ■ 379
Conanicut arkose 380
Rose Island and Coasters Harbor Island arkose 380
Chapter XI. — The pre-Carboniferous rocks of the southwestern portion of the Narragansett
Basin 381
Little Compton and Newport Neck shales 383
Quartzites of Natick 383
Chapter XII. — The Cambrian strata of the Attleboro district 386
Cambrian brook localities 388
Localities 1 and 2, southwest of North Attleboro 388
Valley of locality 3 392
Locality 4, northeast of Diamond Hill 393
Maps and sections 394
ILLUSTRATIONS.
XVIII. Contact of pegmatites witli Kingstown shales, Watsons Pier, Rhode Island 242
XIX. Coarse pegmatites of AVatsons Pier, Rhode Island 244
XX. Cross-stratification in pebbly sandstone of Kingstown series, Devils Foot
Ledge, Rhode Island 248
XXI. Sandstone-gneiss of Kingstown series, Devils Foot Ledge, Rhode Island 334
XXII. Stratification and slaty cleavage, Aquidneck shales, eastern shore of Prudence
Island 350
XXIII. Wave-cut bench in Aquidneck shales, western shore of Prudence Island 35S
XXIV. Fretwork weathering of Aquidneck shales, Prudence Island 362
XXV. Pegmatite dikes cutting Kingstown shales, Watsons Pier, Rhode Island 376
XXVI. Hoppin Hill, a granite mass surrounded by Cambrian, North Attleboro,
Massachusetts 38t
XXVII. Sketch map of the North Attleboro Cambrian localities 388
XXVIII. Sections in the Narragansett Bay region 394
XXIX. Sections in the Narragansett Bay region 394
XXX. Sections in the Narragansett Bay region 394
XXXI. Geological map of the southern part of the Narragansett Basin 394
221
GEOLOGY OF THE NARRAGANSETT BASIN.
PART IIL-THE SOUTHWESTERN PORTION OP THE BASIN.
B)^ Aug. F. Foerste.
CHAPTER I.
INTRODUCTION.
DIFFICULTIES OF THE FIELD.
The writer first studied the geology of the Narragansett Basin in the
summer of 1887. Thereafter he spent a part of each summer in this field
imtil 1890. His investigations during this time were confined almost
entirely to the region around North Attleboro, and some attention was
given to tracing the present margin of the Carboniferous basin. In the
course of the latter Avork about three months were spent on the southern
half of the Carboniferous basin. Some of these studies Avere recorded in
a thesis, "On the Igneous and Metamorphic Rocks of the Narragansett
Basin," 1890, deposited in the library of Harvard College. In the early
summei of 1890 a short stay at Newport convinced the writer that an order
of succession of the Carboniferotis rocks could be made out, having- the
following character: (1) At the base a series of shales, now known as the
Aqnidneck shales; (2) above these, sandstone beds with some small pebbled
conglomerates, now known as the Sakonnet beds; (3) a verj^ coarse peb-
bled conglomerate, then already known as the Purgatorv conglomerate.
He then went to Swansea, around the margin of the great Dighton con-
glomerates, in order to see whether a similar succession could be made out
223
224 GEOLOGY OP THE ISTAERAGAI^SETT BASIN.
there. While in the midst of this work he was called away fi'om this field
to another division of the Survey. Only about four months had therefore
been spent by the writer in this southern portion of the basin previous to
the present summer (1895), when two additional months were occupied in
field work. This report is the outcome of the observations made at these
various times. No one can understand better than the writer both the short-
comings of the report and the difficulties of the field. While exposures are
numerous in various parts of the basin, chiefly along the shores of the main-
land and the numerous islands, they are so widely separated by the arms
of the bay and by broad areas of sandy soil that an interpretation of the
structural relations existing between the exposed rocks is exceedingly diffi-
cult, if not impossible. Under the circumstances, however, it is hoped that
the report will at least add something to our knowledge of the basin and
furnish a basis for future labors and rectifications.
As the result of much thought and care in the study of the exposures
actually found, although within a limited time, the writei' will express the
following opinions: Isolated exposures of small extent, unless within an
area of frequent exposures, are apt to be more misleading than serviceable
in the identification of horizons, owing to locally sitdden lithological
changes, especially in areas occupied by the Kingstown series. Greatest
weight in making out geological horizons and the order of succession should
always be given to long lines of exposure. It is not considered advisable
to attempt a division of the Carboniferous rocks into separate geological
horizons until an acquaintance is made with the scattered Carboniferous
exposiu-es over a very large area — in fact, over at least half of the area
investigated — since otherwise the importance of features of only local value
is easily magnified.
It may seem trite to express such opinions, in view of the advanced state
of methods of geological investigation, but these remarks are especially
pertinent to the Narragansett Basin, where the investigator of a limited
field, especially in the dubious country in southern Aquidneck, is liable to
go astray on account of the absence of exposures at very critical points.
Nowhere are isolated small exposures more liable to influence opinion as
to the geological succession of neighboring larger rock masses than here,
and nowhere is the possibility of consequent erroneous views greater, but
the attempt has been made to overcome these difficulties, and it is hoped
with at least a measure of success.
mTKODDCTlOK 225
ARRANGEMENT OF REPORT.
A reference to the accompanying map (PI. XXXI), illustrating the
geology of the lower part of the Narragansett Basin, will show that more
than half of the area investigated is covered by the waters of Narragansett
Bay and its many ramifications, A large part of the remaining area, especi-
ally along the shore and on certain islands, is covered by sand and various
glacial and more recent deposits. The rock exposures occur chiefly along
the shore Much of the geology is necessarily uncertain, and the writer
claims only such an advance in the knowledge of the geological features of
the region as a careful study of the meager data will admit. In preparing
his report it seemed desirable to describe first the geographical distribution
of the various rock exposures, their lithological characteristics, and their
strike and dip, without any special reference to conclusions which might be
drawn from these (Chapters II-VI). This seemed preferable, since the
exposures furnish the basis for all conclusions, but the inferences drawn
are not always as imperative as in the case of other geological fields where
exposures are more frequent or admit of more ready interpretation. While,
therefore, a description of the exposures would have permanent value, the
interpretation of the geological structure might vary with the increase of
our knowledge of the geological data involved. Many localities, at present
still concealed by the soil, are likely to be exposed in the future by the
construction of roads or the digging of wells, foundations, and sewers.
The correlation of the beds exposed in various parts of the field, and the
conclusions concerning their relative age, receive special attention in the
later chapters of the report (Chapters VII-XI).
The description of localities in geographical order is begun in Chapter
II with Dutch Island, the most western locality in the southern part of
Narragansett Bay in which fossils have been found. In going from this
island to Fox Hill and the northern part of Conanicut we remain in the
same series of rocks, and are better prej^ared to understand the differences,
stated later, between the Kingstown beds and the Aquidneck shales, which
occupy most of the remainder of the island. After this, Hope and Prudence
islands ai-e desci'ibed, these islands being more nearly in line of strike with
Conanicut than with other regions southward, and presenting rocks at least
of approximately similar horizons.
MON XXXIII 15
226 GEOLOGY OF THE NARRAGANSETT BASIN.
Chapter III is devoted to a discussion of the exposures on the western
side of the bay. Directly west of Dutch Island lies Saunderstown. The
shore exposures south of this locality show lithologically all the features of
the Carboniferous of Dutch Island and northwestern Conanicut, so that,
although fossils are not found, the geological position of the beds is fairly
certain. Southward, however, metamorphism becomes more pronounced,
the Carboniferous exposures are no longer so continuous, they are separated
by large pegmatite intrusions, and finally appear only as rare inclusions
in the pegmatitic granites of Boston Neck and Nai-ragansett Pier. The
gradual character of these changes prepares the student for the conclusion
that even these southern rocks and the Tower Hill exposures are Carbon-
iferous. From this region northward the Carboniferous age of the rocks
must be conceded.
In Chapter IV the exposures between Providence River and Taunton
River, on the northern side of the bay, are taken up.
Following the eastern shore of the bay southward, it is conveniently
possible, first, to describe all that is accurately known of the Carboniferous
formation on this shore, and then to discuss the probably pre-Carboniferous
rocks of Little Compton. This is done in Chapter V.
In the same way, beginning with the basal arkoses at Sachuest Neck,
it is possible to describe all the more evident stnictm-es of Aquidneck
Island before the more doubtful regions near ]\Iiantonomy Hill, and then
those toward Newport Neck. This is done in Chapter VI.
It has been the Avriter's aim so to arrange the materials as to proceed
from the better known to the less evident facts and structures.
The conclusions founded on these observations form the basis of the
second part of this report, inclnding Chapters VII to XI, and have been
placed toward the close. They are necessarily of a more argumentative
character, and the attempt has been made to bring out more sharply the
inferences deduced from the facts by removing from this part of the report
all unnecessary references to the more minute details of the geological
features presented by the individual exposures. It is this part of the report
which must necessarily be subject to revision, and which nevertheless is
the more important, since it gives the results of the work. No one has had
more occasion to regret the scantiness of continuous exposures in an east-
west direction in this area, across the strike, than the writer, for this has
left his efforts in the field often of little avail.
CHAPTER II.
THE WESTERN ISLANDS OF THE BAY.
DUTCH ISLAND.
From the western side of the island, nearer its northern end, a triangn-
lar piece of sandy beach extends into the western passage of the bay.
Southward from this beach there is a continuous exposure of Carboniferous
rocks along the shore. The more northern portion consists chiefly of black
shales, which sometimes are very coaly. At a point about 400 feet south
of the beach and directly west of the largest building on this shore, a
number of fern leaves were found in the coaly shale, the shale being free
from any marked signs of metamorjDhism, excepting the usual cleavage.
The strike of the shales is N. 30° E.; dip eastward, variable, but very dis-
tinct, averaging perhaps 45°. Sandy layers are more or less frequently
intercalated in the shales. Farther south there is an alternation of sand-
stone and conglomerates with some coaly shales. The strike is N. 30° E.;
the dip is still eastward. Along the last 1,000 feet sandstone prevails.
Here is shown a fine instance of crumpled strata. The layers can be well '
distinguished, and the flexures which they have undergone can readily
be traced. Notwithstanding the flexuring, the dip of the sandstone can
be seen to be distinctly eastward. The strike is nearly north and south, or
slightly east of north. Near the light-house there is not sufficient exposure
to make a determination of the dip. Along the east shore northward
from the light-house the crumpling of the sandstone continues. A fine
exposure of conglomerate, forming a bed about 8 feet thick and free
from crumpling, shows the dip to be about 50° E. The strike is N. 20° E.
The conglomerate borders the western side of an embayment about a third
of the length of the island north of the light-house. The point forming
the eastern side of the embayment consists again of crumpled sandstone,
with a few thin layers of conglomerate, the dip being distinctly eastward
as far north as the wharf, a third of the length of the island from its northern
228 GEOLOGY OF THE NARRAGAKSETT BASIN.
end. The same sandstones with thm conglomerate layers are also found
north of the wharf, as far as the obtuse northeast angle of the shore. The
strike here is N. 16° E., and the dip of the strata, as actually exposed, is
nearly vertical, though a consideration of the more southern exposures of
this series warrants the belief that the general dip is eastward.
In general, the strata of Dutch Island may be described as consisting
chiefly of sandstones with subsidiary conglomerate layers, underlain on the
extreme western border by a series in which black, often coaly, shales pre-
dominate. The general strike is N. 20° E., becoming more directly north-
ward at the south end. The dip is eastward. A continuation of the strike
northward would carry this sei'ies to the western side of Conanicut, at the
southei'n end of the line of exposures corresponding to Slocums Ledge.
Here, in fact, a similar series of rocks occurs, but the strike is more north-
ward (N. 3° E.); the dip eastward. Continuing the strike southward, the
most eastern exposure on Dutch Island sliould pass to the west of Beaver
Head or Fox Hill, the nearest part of Conanicut. Yet, even if this be the
case, there is no doubt that the Fox Hill strata belong to the same general
series, and if the}'" represent a higher horizon there is plenty of room on
Conanicut for the combined series.
The degree of metamorphism shown by the Dutch Island rocks will
be discussed in connection with the metamorphism shown by the corre-
sponding rocks on Conanicut.
COISTAXICUT ISLAXD.
FOX HILL, BEAVER HEAD.
Sandstone and several conglomerate layers are found along the more
western margin of the hill along the shore as far as its southwestern point,
the beginning of the beach. Some of the pebbles of the cong-lomerate layers
are fairly large, and one or two a little over a foot in length Avere found.
The beds containing these pebbles can not be compared, however, with the
Purgatory conglomerates; still, the presence of large pebbles is noteworthy.
Near the southern end of the series of exposures the coaly shales show
considerable crumpling. This becomes less marked northward, where
the strike is found to be N. 18° E., and the dip as low as 30° E. Over-
OONANICUT ISLAND. • 229
lying the sandstone and conglomerates along the entire northern margin of
the hill is a series of black shales, at times very coaly. Intercalated with
the shales were narrow bands of sandstone, indicating a low eastward dip,
sometimes as low as 20°. This eastward dip is significant in connection
with the question of the comparative geological age of the green shale
lying immediately to the east.
NORTHERN HALF OF THE ISLAND, NORTH OF ROUND SWAMP.
The first exposure of rock on the western shore occurs just south of a
very small sand beach, where the coast line of the island begins to take
a direct northern course. Here occurs sandstone witli some thin conglom-
erate layers showing a strike of N. 5° E. and an eastward dip. North of
the beach there is a stretch of coaly shale, with an eastward dip. Then
follows northward a series of sandstones with interbedded conglomerate
layers, as far as a small stream entering the bay near the north end of
Slocums Ledge. Northward coaly shale is again exjDOsed, showing a strike
of N. 8° E. and an eastward dip. Yet north of this is a long sandstone
exposure with a strike of N. 13° E. and an eastward dip. Still farther north
occur coaly shales again, as far as Fowler Rock, near the middle of Great
Ledge. The line of shore exposures above mentioned, which might be
called the ledge exposures on account of their proximity to Slocums and
Great ledges, show the greatest degree of metamorphism among the rocks
of the island. From Fowler Rock to a short distance northeast of Sand
Point there are no shore exposures.
Northeast of Sand Point the shore lies on coaly shales interstratified
with sandstones. The strike is N. 3° E.; the dip is also east. Northward
there are sandstones with minor conglomerate layers, having the same sti'ike.
Farther north is more coaly shale, with intercalated sandstones, with the
same strike of N. 3° E., and this is also shown by the most northei-n
exposures on the western side of the island, coaly shales being exposed just
west of North Point.
Exposures begin again about 1,200 feet east of North Point along the
north shore and continue for several hundred feet. The rocks are chiefly
shales, much squeezed in a direction from east to west, making a strike of
N. 18° E. and an uncertain dip, which is believed, however, to be eastward.
The next exposures along the eastern shore, going south, are almost directly
230 GEOLOGY OF THE NARRAGANSETT BASIN.
east of Sand Point, wliich lies on the ^-estern shore. Here are found gray
sandstones and shales, with a strike of N. 8° E. and a vertical dip. In a
small embayment to the sonth, almost east of the crest of the unnamed
100-foot hill indicated on the map, is black shale, often coaly. In one
of the coaly shale layers in the most indented jDart of this embayment,
fossil fern leaves are not imcommon. The strike is N. 13° E. and the dip
vertical. South of this embayment occurs a line of sandstone, with a
strike of N. 13° E. and a dip which is almost vertical, but slightly inclined
toward the west; but there are very low dips in various directions farther
south, indicating crumpling and folding in the rock. As the shore begins
to curve toward the SSE. exposures are wanting, but farther south there
is a grayish sandstone striking N.-S., with a dip of 70° to 80° E., toward
the southwest of which is a dark shale, and farther southwest occurs a black
coaly shale with a strike N. 9° E. For some distance southward there is an
absence of exposures. Farther south, past the mouth of a little stream enter-
ing the bay, inore of the coaly shale occurs, in the most western portion
of this long embayment. A short distance south of a point directly west of
the southern end of Gould Island black shales occur, with irregular dip and
strike, indicating crumpling of strata. It is near the old feny, and is the
most southern of this series of rocks on the east shore.
A line connecting the small embayment immediately south of the old
ferry with the pond east of Fox Hill would indicate approximately the
eastern limit of the Kingstown sandstones with conglomerates and the coaly
shales. South and east of this line lies the great Conanicut shale series,
which is a part of the Aquidneck shale series, hereafter to be described.
The strike of both the eastern and the western portion of the exposures
in northern Conanicut averages about N. 8° E. Along the western shore
there is no marked crumpling, and the dip is distinctly east, averaging
perhaps 40° to 50°. On the eastern side the dips are frequently vertical,
and sometimes horizontal, as though considerable folding and crumpling
would be shown if there were any long vertical sections across the strike
The western portion of the northern half of the island shows consid-
erably more metamorphism than the eastern portion, and the most meta-
morphosed portion is that bordering the shore along Slocums and Great
ledofes.
GOlSrANICUT ISLAND. 231
Here the pebbles of the conglomerates have been squeezed into thm
sheets, often several inches long' and hardly more than a quarter of an
inch in thickness, so that it is difficult at times to recognize the conglom-
eratic nature of a layer if seen in a section transverse to the cleavage, while
along the plane of shearing the pebbles are very easily recognized. This
flattening of the pebbles is shown to an equal degree in the conglomerate
at the western base of Fox Hill, on Dutch Island, and along the more
northern and eastern exposures on Conanicut.
The sandstones and shales exposed along the shore at Slocums and
Great ledges frequently contain garnets. These are of much larger size
than any found farther north on the island. Grarnets in the sandstones on
the eastern side of Conanicut are very small, and those in the shales are
yet smaller.'
A walk around the border of the island is very instructive. The most
eastern coaly shale exposures are, except for their cleavage, but little affected
by metamorphism, and for this reason it was not difficult to find fossil ferns
there, while along the ledge exposures on the west the frequency of large
garnets, and often also of staurolites, makes the detection of fossil ferns in
these shales very difficult. Nevertheless, Prof T. Nelson Dale found a
number of well-preserved fossil ferns somewhere along the ledge exposures,
in a layer of black coal}^ shale, hardly more than a foot thick, included
between shales containing staurolite, garnets, and ottrelite.
Staurolite was found only along the cliff exposui-es, but in places it
was very abundant. It was not seen on Dutch Island or Fox Hill. Garnets
were found in the shales on Dutch Island, but in some of the shales they
were entirely absent. In the black and coaly shales at Fox Hill they were
rare, although occurring in great numbers in the overlying green schists
south of Fox Hill. At several localities on Conanicut and Dutch islands
radiate aggregates of a greenish mineral are found rather abundantly in
this series of rocks. These aggregates are instructive in connection with
the exposures on Gould Island, in the northern part of Sakonnet River.
While the metamorphism undoubtedly increased in intensity westward, in
this region it did not increase regularly so as to make Fox Hill and Dutch
Island show more metamorphism than the cliff exposures of Conanicut.
' On metamorphism in the Rhode Island coal basin, by T. Nelson Dale: Proc. Newport Nat.
Hist. Soc, Doc. 3, 1885, pp. 85-86.
232 GEOLOGY OF THE NARRAGANSBTT BASIN.
SOUTHERN HALF OF THE ISLAND, SOUTH OF ROUND SWAMP.
SHALE REGION.
The most northern outcrop of the Conanicut shales is in a small
embayment north of Potters Cove, about 1,800 feet south of the old ferry.
They are here very thin and fissile. They are again exposed for quite a
long distance along the northern part of Potters Cove. At its southern
extremitv, and thence all around the margin of Freebodys Hill and beyond
Jamestown Ferry, there is an almost continuous exposure, the outcrops
ceasing about half a mile south of the ferry point. At Taylors Point the
shale contains quartzitic layers. If these are original interstratified sandstone
layers there has been much lateral crumpling. Nevertheless, the beds show
a generally low dip. Along the eastern shore of Freebodys Hill there is
distinct color banding, accompanied by considerable crumpling. The most
northern of the outcrops of the shales along the western shore lies within
half a mile north of the western Jamestown ferry. Thence outcrops occur
at more or less frequent intervals as far as the marshy land, a short distance
south of the western ferry; then, after a short interval, along the eastern
shore of Mackerel Cove. Shales occur again a third of a mile south of the
western ferry, along the southern margin of Dutch Island Harbor, on the
northern edge of tlie southern half of Conanicut, east of the pond near
Fox Hill. South of Fox Hill they occur again at the end of a beach about
a sixth of a mile long. Here they are very glistening and are filled with
some ferruginous mineral, not closely examined in the field, but probably
pyrite. Thence the same shales are found around the entire margin of this
part of the island, around Beaver Tail Head, thence northward into Mack-
erel Cove to its northern extremity, and thence from the eastern end of the
sand bar connecting the two parts of the island, down the eastern side of
the cove, to a point where a small stream enters the cove.
Two minette dikes cut the Conanicut shales in the southern half of
the island. One dike extends from the northern side of Hulls Cove to the
northern edge of Austins PIollow ; the other extends from Lions Head to
the Southern edge of Austins Hollow.
The color of the Conanicut shales is somewhat variable. Where dry
and long exposed to the action of weathering they are lighter in color,
verging toward greenish, with a tint of blue or brown; where wet they
CONANICUT ISLAND. 233
are darker in color, usually dark blue, often almost black, but not of the
dense black hue characteristic of the shales often called coaly in this paper,
in which fossil ferns are usually present. These shades of color are also
found where they are not due to variations of moisture, but in general the
dark-blue type prevails, excepting- in the more weathered portions. Dark
color banding not infrequently indicates the true dip and strike. While the
general strike is undoubtedly northerly, the dip is not so easy to determine.
While the writer believes that the series of shales as a whole overlies
the series of sandstones, conglomerates, and coaly shales already described,
and while an easterly dip would best accord with such belief, it is only
proper to mention that the time at his disposal did not enable him to make
a satisfactory study of the problem. The dips on the western side of the
shale series were often found to be very steep, almost vertical, and in some
very large exposures more or less steep westward, while on the eastern
side, as far as the northern part of Mackerel Cove, the dips were less vertical
and were often eastward. The chief reason for believing that the Conanicut
shales are above the Kingstown sandstone conglomerate and coaly shale
series is their occurrence east of the latter, especially east of Fox Hill, and
the uniform eastward dips of the latter series, especially at Fox Hill, but
also on Dutch Island. Unfortunately, the uniform east dip along the western
margin of northern Conanicut is not continued in an equally ajDparent man-
ner in the more crumpled and folded series on the eastern side of the island.
GRANITE AREA, THE DUMPLINGS, AND ARKOSE REGION WEST OF THE DUMPLINGS.
Coarse granite, in part filled with large phenocrysts of orthoclase, occu-
pies the southern end of the northeastern half of Conanicut, from the
southern side of Bulls Point to Mackerel Cove. North of the granite, on
the Mackerel Cove side, is a considerable exposure of arkose. Near the
granite the arkose contains some of the large phenocrysts of orthoclase
derived from the granite, scarcely broken up. Farther from the granite the
large phenocrysts are more rare. Interbedded with the arkose are more
carbonaceous, sandy, and shaly layers, with strike about N. 70° E. near
the granite. The arkose is exposed along Mackerel Cove as far as a little
stream entering the cove from the east. North of the mouth of this stream
only the Conanicut shale series is exposed. The color banding of this shale
234 GEOLOGY OF THE NARKAGANSETT BASIISr.
is at several points very distinct, and a careful examination of the same seems
to indicate that the shales strike more nearly north-south, and dip at a low
angle eastward. The stream indicates a line of fault between the shales
and the arkose beds.
The relative age of the arkose beds and of the green Conanicut shales
is not known. The arkose beds are undoubtedly Carboniferous. They
give evidence of interbedded layers of somewhat carbonaceous shales.
Some of these shale layers were thin, and suffered enough erosion from the
variable ciirrents present during the deposition of the grit to cause the
remnants of the shale layers to appear like fragments of shale inclosed in
certain courses of the grit. The green Conanicut shales are also Carbonif-
erous. But there is no gradation of the grit into the Conanicut shale
immediately to the north. Those parts of the arkose and of the Conanicut
shales actually exposed along Mackerel Cove are therefore not .strictly of
the same age, although both are of Carboniferous age. A line of fault
separates them. Since neither the upthrow nor the downthrow of the fault
is known, it is impossible to determine by comparison of their exposure
which is the older.
Nortli of the eastern half of the granite area is found a greenish rock,
here called the Dumpling rock. In places, especially in the northern out-
crops along the shore, it is purplish, looks very much like an argillite, and
seems to show genuine stratification. Farther south along the shore, at a
promontory, it seems to contain pebbles. Still farther south, however, and
along all the inland exposures, from the eastern side of Conanicut, along
the northern margin of the granite area, toward the cove, the Dumpling
rock is greenish in color, fine grained, of homogeneous texture, gives no
evidence of clastic origin, is cracked in all directions, and does not have
the appearance of a stratified rock. It bears a strong resemblance to the
greenish rock found along the southern Newport Cliffs south of Sheep
Point. To a less degree it resembles the greenish and purplish rock form-
ing the middle third of Newport Neck. The most northern outcrop of
this greenish rock is along the shore half a mile south of Jamestown
Ferry. Thence it extends inland for half a mile in a southwest direction.
Here the northern boundary seems to meet the southern in a sharp angle
(see map, PL XXXI). The gi-anite area lies but a short distance southward,
and the northern border of the granite passes irregularly eastward, south of
the Dumpling rock area, at first about N. 70° E., then S. 70° E. to the
HOPE ISLAND. 235
shore a third of a mile northwest of Bulls Point, then reappearing on the
promontory of Bulls Point, forming the northeast shore of the promontory
to its extremity. The southern part of the rock island southeast of Bulls
Point is granite. All the rock islands north and northeast of Bulls Point,
including the Dumplings, are foi-med by the greenish Dumpling rock. This
Dumpling rock is older than the granite. This is shown by the fine-granied
structure of the granite wherever it comes in contact with the Dumpling
rock. The greenish Dumpling rock along a road near the contact half a
mile northwest of Bulls Point, and along the point itself, is penetrated by
dikes of pink or reddish aplites of rather fine grain. This aplite is still
more common in the granite area, and evidently represents a later intru-
sion, after the great granite mass had cooled considerably. Sometimes the
aplite is rather coarse, biit never so coarse as the granite mass itself. The
Dumpling rock is considered an argillite, formed by the raetaphoric action
of pre-Carbonifei'Ous granite on still earlier, ^Jossibly Cambrian, shaly rock.
At no point does the greenish Dumpling rock of Conanicut come in
contact with the Conanicut shale series at the surface. The Clearest points
of approach are at least several hundred yards distant. The arkose may
once have extended along the northern part of the greenish Dumpling rock
toward northern Rose Island and southern Coasters Harbor Island. There
is certainly a great temptation to assume the existence of an island^ in Car-
boniferous times, consisting of granite, Dumpling rock, and the Brenton
Point shales. This island would include the Newport Harbor Islands south
of the line above mentioned, the area east of southern Mackerel Cove on
Conanicut, and Newport Neck. Kettlebottom Rock, a short distance south
of the southwestern end of the granite area, consists of Conanicut shale.
HOPE ISLAND.
The pier is at a pi'ojection about 900 feet south of the northeast angle
of the island. From the em.bayment on the eastern side of the island south
of the pier to a similar indentation on the western shore an east-west
fault seems to run. The beds both north and south of the pier seem to
have very steep dips, with variable strike. At the northeastern angle of the
island, however, they dip at a low angle northeastward. The rock at this
end is a white quartzitic sandstone with few pebble layers. Westward
' T. Nelson Dale : Ara. Jour. Sci., 3cl series, Vol. XXVII, 1884, pp. 217-228, 282-289, map.
236 GEOLOGY OF THE NAERAGANSETT BASIN,
along the northern margin of the island black shales and fine-grained sand-
stones underlie the sandstone, dipping northeastward. Farther west, extend-
ing from the northwest angle of the island to the indentation northwest of
the dwelling house, is more white quartzitic sandstone, dipping under the
black shales at a low angle to the northeast. Near the southern end of
this part of the shore a black shale layer is seen to underlie the sandstone.
South of the fault line, on the west shore, are found in succession the
following rocks, numbered downward in the section :
(1) Black shaly rock, strike N. 30° E., dip 80° E., the strike continu-
ing far southward.
(2) Conglomerate with small pebbles and with flakes of black shales
in the lower courses.
(3) Black shale.
(4) A considerable thickness of sandstone, becoming conglomeratic
southward along the strike; dip about vertical, becoming 60° W., then 45°
W., then more nearly vertical, and finally, on going southward, 70° E.
again.
(5) Black shales adjoin the sandstone on the west. This black shale
layer makes its appearance in the projection southeast of Gooseberry Island
and continues to be exposed or otherwise indicated for a distance of 1,000
feet. The strike is parallel to the shore, and the dip is 70° to 60° E.
(6) West of this black shale layer occurs sandstone, more black shale,
and again sandstone on the shore southeast of Seal Rocks.
(7) East of this long black shale layer occurs a great mass of sand-
stone as far as the south end of the island, becoming conglomeratic along
the eastern side of the island, being there often a rapid altei'uation of sand-
stone and conglomerate layers. Along the eastern side of Hojje Island the
dips are low eastward, usually 30° to 45°.
The sandstones of Hope Island are very white and quartzitic, but abun-
dantly specked by some small black micaceous mineral, probably biotite.
The blue and gray color ot the standstones, so characteristic in less meta-
morphosed regions, has disappeared. Pebbles are present to a certain meas-
ure ill all the sandstone layers, but on the western side of the island the
sandstone predominates greatly, while along the eastern shore almost half
of the rock is conglomeratic. The black shaly and evidently Carboniferous
beds are found only along the western and northern shore, and evidently form
PRUDKNOE ISLAND. 237
the lower beds of the small section here exposed. These shales are every-
where filled with dark minerals, which in some cases resemble, macroscop-
ically, ottrelite, and in other cases may be some other dark micaceous
mineral. The pebbles of the conglomerate are uniformly small, usually
not over li inches in diameter. Many of them are distinctly quartzitic or
granitic; in the latter case of medium grain, of bluish tint, and without
phenocrysts.
There has been no flattening of pebbles or considerable shearing,
metamorphism being, however, abundantly shown by the frequent presence
cf black mica in the sandstone and of ottrelite in the black shales.
A continuation of the strikes along the entire Avestern margin of
Conanicut would carry the series there exposed to Hope Island. The
form of the sea bottom between these two islands also suggests a general
continuity of strata, and the rocks exposed on Hope Island are believed
to belong to the same general series as those exposed on Conanicut, although
possibly just beneath that series, as is indicated by the more quartzitic
phase and the general absence of the more argillaceous or slaty pebbles,
the latter being more frequently quartzitic and granitic. At Hope Island,
however, the strikes are much more toward the northeast, averaging N. 30°E.
A continuation of the strike would carry these rocks toward Johnsons
and Pine Hill ledges south of Pine Hill Point, on the western shore of
Prudence Island. Whether they occur there could not be determined.
PRUDEINCE ISLAND.
The lowest rocks exposed on the west side of the island are found
north of Prudence Park wharf, and continue thence northward, forming
the shore for a little over a mile, with an average strike of N. 20° E.
and a dip of 25° to 45°, at one place 60° E. The average dip is about
35°. At the wharf the sand.stone is bluish, with a few thin conglomerate
layers. The pebbles are elongated, but much less than at Hope Island,
and the general metamorphism is evidently less. The sandstone series
appears again about a quarter of a mile northward, at the end of a long
inward curve of the shore, where it contains thin conglomerate layers.
Thence it follows the shore northward, the shale series often appearing in
contact with the sandstones on the eastei'u line of outcrop, on the top of
the bank. Black carbonaceous streaks often band the sandstones. At some
238 GEOLOGY OF THE NARRAGANSETT BASIN.
points the cross bedding is well marked. Thin but elongated pockets of
ottrelitic coaly shale are found in places not far northward. Within 2,700
feet of the wharf scattered pebbles, sometimes 3.^ inches long, not at all
flattened, occur in the sandstone. In a few of these pebbles oboli were
found. The oboli occur again northward in a thin layer of conglom-
erate, the pebbles of which are sometimes 1^ inches long. The oboli are
found once again, about 700 feet north of the first-mentioned locality,
in pebbles scattered through the sandstone. The gray sandstone is not
infrequently banded with more carbonaceous layers. Farther north long,
thin fragments of carbonaceous shale occur in small conglomerate layers.
A little more than three-quarters of a mile from the wharf the flattened
leaf-like plant remains occur, such as are found at Hills Grove, Warwick,
and Silver Springs, East Providence. The outcrops along the shore cease
about a mile north of the wharf. Northeastward of this, in the field, a
sandy outcrop, probably belonging in the next higher series, occurs. In
general, the series here described is composed of sandstones. The absence
of coaly shale layers in it does not signify much, since the vertical section
here exposed probably does not exceed 50 feet.
The occurrence of a shaly series over that of sandstones all along the
line of outcrop has already been noticed. This shale series is well exposed
along the long inward curve of shore north of the wharf The lower
courses immediately over the sandstone look very much like the dark-blue
shales of the Conanicut series, but frequently contain ottrelite and are
banded with more frequent and much larger layers of a very fine grained
sandstone, which has been less affected by shearing. Above these beds
occur decidedly coaly shales, often siliceous from the presence of minute
clastic quartz grains. Above these again occur the fissile dark-blue shales.
The color banding of the shales is often very well shown, and since there
has been no crumpling, or violent folding, it indicates the strike and dip very
well. The strike averages N. 20° E., and the dip is about 35° E. The upper
dark -blue fissile shales are exposed at a number of points halfway up the
hillside east of the wharf The very coaly black shales form the shore
south of the wharf for a distance of over a mile. It must not be imagined
from this that the coaly shales are perfectly distinct from the dark-blue
members; on the contrary, they are interbedded with the dark-blue shales
at various levels, but nowhere else in the series is so much coaly sliale
PRUDENCE ISLAND. 239
found as at this level. The general strike is parallel to the shore, about
N. 10° E. south of the wharf, and N. 3° to 5° E. farther south. The dip,
which is 25° E. for the g-reater part of the shore exposure, becomes 40° E.
near the southern end. Here there is also much local crumpling, which
brings the color bands of the rocks often to a vertical position. The
crumpling takes place in a direction N. 60° E.
South of the wharf the coaly shale often shows distinct color banding.
Gray, rather coarse sandstone occurs along the top of the cliff. The shale
is frequently ottrelitic About 3,375 feet south of the wharf fossil ferns
were found in the coaly shales, where finest gi'ained and least ottrelitic.
Ferns are difficult to find in this series. It is best to take each slab of shale
in the hand and hold it so that the sunlight will bring out in sharper relief
all the unevenness of the surface. When the fern-leaf impressions are once
found, the character is readily enough recognized. In the sandstone which
occurs in the coaly shale series at this point was found the impression of a
very large calamite. The longitudinal ribs were very coarse and distinct,
and although the specimen was about 14 inches long and 4.^ broad, yet it
showed not a single joint.
The most northern exposure on the east side of the island occurs about
two-thirds of a mile north of the light-liouse at Sand Point. Here is found
a rock belonging to the shale series, finely color-banded, very micaceous,
but not fissile. The strike is N. 12° W. and the dip 75° W. The next
exposure is hardly half a mile north of the light-house. It is very dark-
blue ottrelitic rock, belonging to the shale series. Its strike is about N.
4° W. and its dip about 80° W. From the south side of the light-house
southward for a distance of 1^ miles there is a continuous exposui-e of the
shale series along the shore, after which Ithere are several more isolated
exposures for about a quarter of a mile farther. The rocks on this side
also belong to the shale series, although evidently higher than the basal
part of that series as exposed on the west shore, since neither the sand-
stone-conglomerate series below nor the lower black coaly shale layei's are
here exposed. These shales usually appear so different from the Conanicut
shales that at first sight their close similarity might not be recognized, jet
careful observation will show at once the same sericitic micaceous structure.
The rock is usually rather firm, but frequently the shaly structure is more
developed and then the rock resembles in every particular the greenish and
240 GEOLOGY OP THE NARRAGANSETT BASIN.
the clark-bluish shales of Conanicut. The color banding is iisually very pro-
nounced, and since the contortion and folding of strata is less, the general
strike and dip of the rocks can be readily determined. These shaly rocks
differ considerably from the Conanicut shales, however, in the more fre-
quent presence of sandy courses, varying from 1 inch to 8, 12, and even 20
inches in thickness. These have usually been less affected by cleavage.
There are also distinctly conglomeratic beds present, although these, except
in the case of two beds, occur only in very thin layers. Darker, more
coaly phases are present in the shales, more carbonaceous than any
observed on Conanicut. The general color of the shales on the shore,
where not moistened by water, is often, for rather long stretches, a peculiar
silvery green, which resembles some phases of the greenish shales at Eas-
tons Point. The darker shales are frequently ottrelitic. Notwithstanding-
all these differences, a person acquainted with the varying aspect of this
series will readily satisfy himself as to its identity with the Conanicut shales.
The general strike for a distance south of the wharf is N. 10° E., dip
70° W. About five-sixths of a mile south of the light-house the shale is
darker, more carbonaceous, and ottrelitic. Farther south thin conglom-
erate beds show stretched pebbles, usually not exceeding half an inch in
leno-th. Yet farther to the south more carbonaceous black shales occur close
to the inward curve along the shore. Farther on there is conglomerate
with pebbles an inch long, and a little over a mile south of the light-house
a 3-foot layer of conglomerate is found with pebbles often 3^ inches long.
The pebbles are usually greenish, as though lithologically similar to the
shales; they are rarely quartzitic. Still farther southward more ottrelitic
dark shale is seen. Fine color banding is often shown. Cross bedding is
common iu the coarser sandstones. Thin conglomeratic layers begin to
be more frequent. Near this point the continuous exposures cease. At the
southern end of these exposures the strike is N. 20° E., the dip still 70° to
80° W.
At the next exposure southward there occurs a more carbonaceous
form of the shale, black and ottrelitic. Strike N. 28° E., dip 60° to 70°
W. The next exposure, more greenish, gives again strike N. 13° E., dip
88° W. Banded, slightly ottrehtic shales form the last exposure, 1| miles
south of the hght-house ; strike N. 33° E., dip 80° W.
PECTDENOE ISLAND. 241
Potters Hotel is located two-fifths of a mile directly west of the light-
house. Southeast of the hotel, in the fields, at several localities, some of
them halfway down the hillside, occur fairly coarse sandy layers, some-
times slightly conglomeratic, accompanying the dark-blue shales. They
represent higher horizons in the shale series, and form the highest land
surface on the island. Their strike is about N. 10° E., the dip 80° W.
The strike on both sides of the island, in the section crossing near
Potters Hotel, is approximately pai'allel to the shore. The rocks on the
western side dip east, those on the eastern side dip more steeply west, and
the general structure of the island is believed to be a syncline. The wash
of the waves has cut a bench into the east-dipping shales south of the wharf
on the western side of Conanicut (PI. XXIII, p. 352). That the rocks on
this island have been less metamorphosed than those in Hope Island has
alread}^ been noticed.
moN XXXIII 16
CHAPTER III.
THE WESTERN SHORE OF THE BAY.
FROM SAUNDERSTOWZST TO ZSTARRAGANSETT PIER.
ALONG THE SHORE.
About a quarter of a mile south of Saunderstown occurs, along the
shore, black shaly rock, originally a very fine-grained carbonaceous sand-
stone, and a light-colored coarser quartzitic rock, representing an original
coarse-grained sandstone, with but little carbonaceous material. The shaly
rock is full of a micaceous mineral, and also contains black specks, which
in part are probably biotite and in part some other mineral. The coarse-
grained sandstone has black mica abundantly disseminated throughout it,
and not collected in patches as on Hope Island. The strike is N. 20° E.,
dip 40° E. Southward some of the coarse-grained sandstone contains white
mica; yet farther south very small pebbles begin to appear in the sand-
stone, usually in thin layers, forming a small part of the total thickness of
the sandstones. Black, shaly, very fine-grained rock continiTCS to be inter-
stratified with the sandstones. Strike N. 30° E., dip often as low as 25° E.
The pebbles are usually less than 1 inch long, and have been drawn out
and flattened by shearing. At first, black shaly rock and sandstone alter-
nate rather frequently just north of a small stream entering the bay; sand-
stone very largely predominates. South of the brook there is again an
alternation of sandstones and black shales, and the low dip of 30° E.
becomes 40° E., then steeper, until it is soon practically vertical; after
which the dip becomes westward, about 70° W. at first, and finally, at a
point 1,250 feet north of the South Ferry wharf, it is 40° W. Here the
section is cut off' transversely to the strike by a large pegmatite dike.
South of this dike the lowest rocks are black shales, almost horizontal, over-
lain by quartziferous sandstone with white mica, containing small pebbles,
overlain by black shale dipping 20° E. The low eastward dip continues.
THE BONNET. 243
almost as far as a very large pegmatite dike about 600 feet north of the
South Ferry wharf, just north of which the dip becomes low west. South
of this pegmatite dike the low eastward dip continues.
North of South Ferry wharf occurs a considerable thickness of sand-
stone of rather small grain and somewhat bluish color, with black shale
higher in the bank. South of the wharf lig-hter-colored sandstone appears,
with very small pebbles and darker, more shaly rock, strike N.-S., dip
70° E. Farther on there is no exposure for a little over half a mile, until
the northern end of the Bonnet is reached.
At the north end of the Bonnet there is sandstone with strike N. 8° E.,
dip low east. A very large pegmatite dike occurs at the northeast angle of
the Bonnet. South of this dike the strike is N. 8° E., dip 60° E. From
here to the southern end of the Bonnet there is an alternation of sandstones
and black carbonaceous shaly rocks. The thickest bed of the black shale
has a thickness of at least 40 feet. The strike at the south end remains the
same, N. 8° E.,dip steep east, near the water's edge as low as 45°; steeper
higher on the banks, as high as 60° or 70°. Whether this indicates a local
flexure or a syncline toward the east can not be determined. Some of the
sandstones are very quartzitic, with much white mica. West of Bonnet
Point is a rapid alternation of sandstones and black shales as far as the
beach. The frequency of coarse quartz grains in some of the sandstones
is noticeable. Strike N. 8° E., dip 60° E.
At the west end of the beach south of Wesquage Pond, the Carbonif-
erous series is exposed again. The beds are here micaceous sandstones
with darker layers. The strike is parallel to the shore, N.-S., dip 15° E.
The Carboniferous series terminates about 200 feet south of the first
exposure, in contact with a very thick, coarsely pegmatitic dike. This dike
borders the shore southward for a long distance (Pis. XVIII, XIX, XXV),
but about 1,200 feet north of Watsons Pier it includes small fragments of
the Carboniferous sandstone, and almost surrounds a very large mass of the
Carboniferous. The dip of this great block is still east. The large area
toward the east of the large pegmatite dike which follows the shore is
believed to be all imderlain by Carboniferous rocks now worn away by the
sea and covered by its waters.
Where the south trend of the shore changes to the southeastward, toward
Watsons Pier, the sti-ike brings these hidden Carboniferous rocks again into
244 GEOLUGY OP THE ]S"AREAGANSETT BASIN.
view, with a strike fault contact over the pegmatite; strike N. 3° E., dip
45° E. These Carboniferous rocks are chiefly sandstone, very quartzitic,
with white mica, and small specks formed by a black mineral. Some more
carbonaceous, darker courses come in just north of the boathouse. Alterna-
tions of the sandstone and darker shaly rock continue as far .as 120 feet
beyond Watsons Pier; strike N. 7° W., dip 60° E. Lighter and darker
colored sandstones continue to form the shore imtil it begins to turn south-
westward, but an unusually large mass of pegmatite borders it on the east.
West of the angle just mentioned, which is a southward-projecting point of
pegmatite, the Carboniferous sandstones are seen again, with the same
strike, but with a nearly vertical dip. Along the shore southwestward
the Carboniferous rocks are exposed almost as far as the mouth of a small
brook, although frequently intersected along the bedding by pegmatite
veins, often of considerable size. The more western courses are decidedly
black carbonaceous shales. Before reaching the mouth of the little stream
pegmatite occurs in great abundance.
About three fourths of a mile south of Watsons Pier the coast makes
a projection a little like the Bonnet, but smaller. This projection is formed
by a rock looking in general like an ordinary light-colored granite, though
showing pegmatitic veining and peg'matitic structui-e in blotches. West of
the south end of this projection, and directly west of Whale Rock, there
appears dark shaly rock, with some sandstone The sandstone is in places
made up of very coarse quartz grains. Some of the shaly rock is very
carbonaceous; strike N. 25° E., dip about vertical. Along the more
southerly trend of the shore the Carboniferous rock is at first not exposed,
although the occurrence of the pegmatite offshore only in the form of
narrow dikes indicates the presence of the intersected clastic rocks, but
farther south there is seen a conglomerate with pebbles from one-fourth to
one-half an inch in diameter, quartzitic as a rule. The angle northeast of
the Clump Rocks is formed by pegmatite.
The western of the Clump Rocks at the light-house is formed by an
ordinary granite rock of medium grain with pegmatitic dikes and blotches.
It includes near the top a mass of Carboniferous quartzitic sandstone, with
very many biotite flakes. The included piece still has an eastward dip. At
the water's edge on the west side is a long mass of Carboniferous rock of
NAREAl^ANSETT PIEK. 245
considerable length, of darker and finer grain, showing the carbonaceous
character of the inclusion. Strike of the same, N. 16° E., dip 45° E.
A third of a mile northwest of the Clump Rocks the pegmatite incloses
a small fragment of Carboniferous shaly sandstone.
The eastern and much larger hill of Boston Neck shows frequent
pegmatite exposures on the eastern side toward the top, directly west of Bon-
net Point, and over a considerable area near its southern termination, south
of Watsons Pier. It is more probable, however, that this hill is composed
of pegmatite and Carboniferous rocks in frequent alternation than that it is
underlain by pegmatite alone. The more western hill contains numerous
exposures of granitic rock verging into pegmatite, near the Narrows, and
a few exposures of the same rocks on the western side.
On Little Neck there are frequent exposures. They were not carefully
searched, but all the rocks examined were granitic, usually medium grained,
whitish or reddish, cut by pegmatite dikes or containing blotclies of peg-
matite, the pegmatite being unusually coarse just west of the north end of
Beach Pond, where the micfi plates are at times 6 inches broad.
Between the two old wharves at Narragansett Pier, east of the Casino,
the Carboniferous rock is seen again, included as a very large block in the
granitic rock. It is chiefly sandstone, decidedly quartzitic, with white and
black mica, the latter more common along certain layers parallel to the
stratification. There is considerable crumpling in this rock, especially
toward the south end. The rock contains also a layer of conglomerate.
The pebbles are so much drawn out and flattened along the plane of schis-
tosity that they appear as indistinctly bordered whiter blotches on the general
rock surfaces; but transverse to the schistosity, especially along their shorter
diameter, their outline is often fairly distinct. They are usually one-fourth
of an inch thick, rarely more than a third of an inch, with a width of 1 to
1^ inches and a length of 3 to 4 inches. No one who had followed the
Carboniferous series in the order here indicated would fail to recognize the
Narragansett Pier exposure as belonging to this series.
The granite at the pier is reddish and often pegmatitic. The exposures
were followed southward for 2 miles along the shore. It is undoubtedly
the same granite as that on Little Neck and Boston Neck. Since it includes
fragments of the Carboniferous series, as well as intersects the strata of this
series, it must be of more recent age. This subject is further discussed
246 GEOLOGY OP THE NARRAGANSETT BASIN.
in the chapter on the arkoses and conglomerates of the Narragausett Bay
region (Chapter X).
WEST OF THE COVE AND PATTAQUAMSCOTT RIVER.
Pattaquamscott River and the cove toward the southwest were once
probably occupied by the Carboniferous series, now removed by erosion,
excepting along the western side of the valley formed by the eastern side
of Tower Hill. At the southern end of this hill, north of the railroad,
the rock is very quartziferous and schistose. The schistosity strikes
N. 80° E. and dips 60° N. In certain layers the rock is full of pebbles,
chiefly quartzitic, but with also some granitic ones. The pebbles are very
much elongated and flattened, as at the pier exposure. Farther northeast
the conglomerate pebbles are still more drawn out. The pebbles usually
are white, bordered by a greater accumulation of black mica than is found
in the general mass. As the lengthening of the pebbles continues, a point
comes where there appears an alternation of whiter and darker thin bands,
in which only a person familiar with such studies would still recognize
the pebble. This limit has here been reached. Farther down the hillside
some of the larger quartzitic and granitic pebbles are less drawn out, and
can easily be recognized. Some of the larger ones are 1^ to 2 inches long.
Below the hotel, farther northeast, the rock is well exposed. From the
southern end of Tower Hill, as far as the hotel, the Carboniferous rocks are
frequently cut along the schistosity by dikes of ordinary granite, and also
by the pegmatite phase of the same, into which it merges in some places,
while at others the contrast is sharp. The result is a rapid alternation of
clastic Carboniferous rock with these granitic and pegmatitic dikes, espe-
cially well shown below the hotel. The alternation of Carboniferous rocks
and the pegmatitic granite occurs for a distance of 2 miles along the east
side of Tower Hill. The schistosity dips westward. Going northward no
more Carboniferous rocks are encountered until the old plumbago mine, a
little over half a mile south of Bridgetown, is reached. Above the mine is
a good exposure of a dark, very micaceous, and probably graphitic schist.
The strike of the schistosity here is N. 5° E. and the dip 70^ E. Farther
down the hillside a great quartz vein includes scattered and brecciated rem-
nants of the Carboniferous series; among others, fragments of genuine
black plumbago, unctuous to the touch. The main body of Tower Hill,
WEST OF THE (JOVE AND PATTAQUAMSOOTT EIVBR. 247
and its northward extension, McSparran and Hammond liills, is made up
of the granite, reddish, medium to finer grained, diked and blotched by
pegmatite. Occasionally there is a slight tendency toward schistosity in
some of the outcrops.
The valley of Indian Run was at one time probably also occupied by
Carboniferous rocks. Near the southern end, toward Peacedale, several
exposures of the Carboniferous still I'emain. Directly east of Peacedale,
on the southern side of a steep hill, partly wooded, a strongly metamor-
phosed rock, possibly belonging to the Carboniferous series, is exposed;
strike N. 50° E., dip 70° SE. The rock here has a decidedly gneissoid
structure, being composed of white quartz with white and black micas and
some other black mineral. The darker minerals are often arranged in layers
between the lighter-colored ones. Some of the whiter streaks may repre-
sent original pebbles. Apparently some of the larg-er granitic and quartz-
vein pebbles have suffered less drawing out and remain more recognizable.
These exposures are at the extreme limit of macroscopically recognizable
clastic rocks. Farther up the hillside occurs a reddish porphyritic gneiss,
apparently representing a granite with phenocrysts of feldspar. All rocks
named are cut by the regular reddish granite with pegmatite blotches and
dikes. Similar exposures of the gneissoid — possibly Carboniferous — rock
occur where the road east from Peacedale crosses Indian Run.
On Rose Hill, west of Mooresfield, occurs the granite with pegmatitic
variations. Apparently the more gneissoid form, with crushed and stretched
porphyritic feldspars, also occurs here. Directly north wai'd 2^ miles, on
Congdon Hill, more granite occurs. Some of it is the ordinary type of
these regions, with pegmatitic phases. Other portions appear gneissoid, and
some exposures here are similar to the gneissoid Carboniferous schists east
of Peacedale.
It is evident that the extreme western limit of rocks whose clastic
origin can readily be recognized has here been reached. This is not equiv-
alent, however, to asserting that the original western limit of the Carbonif-
erous deposits of the Narragansett Basin in this direction has been attained.
It is probable that they once extended farther westward, but in the limited
time at the writer's command detailed study of these more western areas
was not possible.
248 GEOLOGY OF THE NARRAGANSETT BASIN.
froji saunderstown to wickford.
North of Saunderstown the same series occurs that is exposed along the
shore from Samiderstown to Nari'agansett Pier. Except for a short distance
between Caseys and Greenes points the exposm'es are all confined to the
more inland districts. Most of the outcrops are sandstones. The softer,
more finely grained, and more carbonaceous sandstones, almost possessing
the character of shales, are more rarely seen than south of Saunderstown.
This may mean that unequal erosion has left their former line of outcrop
beneath the present level of the soil, or that they were rarer in the area
northwest of Saunderstown. The facts noted in the field point rather to a
diminution in the frequency of the darker, shaly strata. The rocks corre-
sponding best to the shale seem to be less carbonaceous than southward,
and merge into fine-grained sandstones only sufficiently carbonaceous to
give them' a very dark, but rarely a really black, color.
Where first exposed north of Caseys Point, the dip of the sandstone
is about vertical. At the beginning of the continuous exposures the strike
is N. 6° E., dip 35° E. The coarser sandstone is very quartzitic, white,
with abundant white mica, spotted with a more scattered black micaceous
mineral. The cross stratification is often marked (PI. XX). This sandstone
contains frequent thin conglomeratic layers, with pebbles up to 1.^ or 2
inches in diameter. The pebbles are usually quartzitic, occasionally gran-
itic. Interbedded with these rocks are darker, more carbonaceous, finer-
grained courses. Going northward toward the quarry a rather thick layer,
more carbonaceous than usual in this more northern area, borders the
shore. Here the strike is N. 10° W., dip 45° E. A pegmatite dike cuts
the rock parallel to the strike. A darker, finer-grained, more ferruginous
dike also seems to occur. The alternation of finer-grained, more carbon-
aceous rock, coarser white sandstones, and occasional thin pebble layers
continues as far as Hazzard's quany. Here the strike is N.° 8 E., dip
perhaps 60° E.
From this quarry westward, as far as the angle in the road connecting
Saunderstown and Hamilton, there are a number of good exposures on the
hillside. The large exposure at the quarry consists almost entirely of white
sandstone. At the house on the hillside tliere occur wide layers of a dark-
blue, very fine-grained shaly rock, which takes the place of the much more
, GEOLOGICAL SURVE'
CROSS-STRATIFICATION IN PEB BLY SAN DSTON E OF KINGSTOWN SERIES, DEVILS FOOT LEDGE, KINGSTOWN, RHODE ISLAND.
FEOM SAUNDEESTOWN TO WICKFOED. 249
carbonaceous shales south of Saunderstown ; dip, 50° E. Farther west the
sandstone contams conglomeratic streaks; dip, 65° E. Still farther west is
sandstone with a few scattered pebbles, rarely 2 inches long. The coarser
sandstones contain fragments looking like altered clastic feldspar grains,
obtained from some more ancient granitic area. Coarser and darker fine-
grained sandstones occur westward as far as the road angle mentioned
above. The next exposure of the section lies on the western slope of
Barbers Height, on the north side of the road toward Hammond Hill and
three-fourths of a mile from the shore; strike N. 10° W., dip 80° E.; coarse
white sandstone and darker finer-grained rock with black mica. On the
south side of the road, hardly a quarter of a mile farther westward,
both kinds of sandstone occur. The coarser contains granite pebbles. A
pegmatite dike is here poorly exposed.
Northward along the trend of the hill called Barbers Height the
coarse white sandstones and dark finer-grained rocks continue to be
exposed. The darker, more carbonaceous, fine-grained shaly rock has a
slightly purplish tinge at several points along the roadside. The most
marked change toward the northern end of the height is a more north-
westerly strike, corresponding to the change in the trend of the granite
hill on the southwest, and a much lower eastward dip, usually not exceeding
40° E.
At the angle of the road, 1^ miles south of Hamilton, on the way to
Hammond Hill, there are numerous exposures. The dips are usually about
30° E. The strikes are northerly, but variable. No sharply defined bed-
ding planes assist in determining the plane of stratification. A pegmatite
dike occurs behind a barn near the southeastern end of the set of exposures.
It is one of the most northerly of these pegmatite dikes in the Carboniferous
area. About a quarter of a mile east of this locality the strike is N. 10° W.,
dip 40° E., well shown. Northward less than a quarter of a mile, at the
angle of the road, the strike is distinctly west of north, how much is
unknown, perhaps N. 20° W., dip 30° E. Northeastward in the field the
strike is N.-S., dip 30° E., well shown. The last exposure, lying north
of a stone wall, shows a change of strike to N. 25° W., dip 20° E., well
shown by dark carbonaceous, fine-grained, shaly rock overlying the
coarser whiter sandstone. Another of these marked changes of strike
250 GEOLOGY OF THE NARRAGANSETT BASIN.
toward the northwest is seen northeast of the hist exposure, near the north-
east end of the most northerly walled field on the hill. Here a strike of
N. 12° W. becomes N. 40° W. in a very short distance northward. The
dip is steeper than usual here, 60° E. The most northern exposures,
near the cove, show a northwesterly strike and an eastward dip of about
35°, as nearly as it can be determined.
The next set of exposures westward is at the angle of the road a little
over a quarter of a mile south of Hamilton. Here the strike is N. 30° W.,
dip 65° E., rather well shown by the contrast of the dark finer-grained and
the coarser white sandstone. The latter, in places, contains very small
pebbles. West of Hamilton a quarter of a mile a road leads northwest-
ward and connects with another road leading to Wickford. Along both
sides of the first road exposures are numerous. One near the road gives a
strike of N. 40° W., dip about 45° E.; there is contoi'tion along the strike.
Along the ridge at the western end of a row of houses, south of a pond,
the strike is N. 12° W., changing to N. 20° W., dip apparently 50° to 60°
E. North of this pond considerable coaly fine-grained rock is shown on
the south side of the road, with apparently a nearly horizontal bedding and
a slight dip northeastward. On the eastern side of the connecting road
to Wickford there are good exposures upon a rather high hill. Toward
the north, one exposure exhibits a strike of N. 18° W., dip 60° E., finely
shown by a very carbonaceous, fine-grained shaly layer in the coarser white
sandstone. In this entire series of rocks the coarser white sandstones pre-
vail; they contain but few pebbles and these are always small. Finer-
grained, more carbonaceous layers, with ottrelite locally, occur here more
frequently than to the westward. Wesf of Hamilton, toward Indian Corner
(marked Allenton on the maps), about halfway between the two villages, a
large exposure on the south side of the road shows a strike of N. 20° W,,
dip 45° E., well exhibited by alternating dark fine-grained rock and white
coarse sandstone. Around Indian Corner, exposures, chiefly of coarse sand-
stone, often with pebbles, are numerous. The strikes are variable, being on
the average N. 27° W., dip 30° to 45° E. A little over half a mile south
of Indian Corner, in the roadside and northeast of the house, a bluish Car-
boniferous sandstone shows strike N. 45° W., dip 50° E. This occurrence
agrees very well with the apparent northwesterly trend of the line of granite
FEOM WICKFORD TO EAST GREENWICH. 251
bordering the Carboniferous field in this direction from Hammond Hill
beyond Congdon Hill.
As already stated, the exposures from Saunderstown to Wiekford and
westward are a northward extension of the series which is developed to
the southward as far as Narragansett Pier.
FROM WICKFORD TO FAST GREENWICH.
Northward of Wiekford, as far as East Greenwich, the rocks last above
described continue to occur, but there is a marked change in their dip, the
general dip being westerly, except on Potowomut Neck, where the strike
swings around to the northeast, and more or less irregular folding gives
both northwesterly and southeasterly dips.
The most western exposures occur about a mile south of Davisville,
along the railroad. Here a bluish sandstone, with conglomeratic layers
and carbonaceous color banding, shows strike N.-S., dip 45° W. East of
these exposures, about half a mile west of the road between Wiekford and
East Greenwich, on the north side of the connecting road toward Davis-
ville, abundant exposures show strike N. 12° W., dip 70° W. Along the
western side of the main road itself exposures are frequent for a distance
of about 2 miles north of Wiekford. One of the more southern exposures,
on a hill west of the road, shows strike N. 40° E., dip very steep, about
vertical, perhaps slightly east. A quarry near the northern end of this
series shows a strike of N. 18° E., dip 85° W., well marked by narrow
carbonaceous color banding in a coarse sandstone. North of this quarry a
short distance a road goes eastward; 1^ miles eastward along this road a
road goes northward. Along this road occurs an exposure of a very car-
bonaceous, possibly ottrelitic, sandstone with strike N. 20° E. and dip
westerly. About 1^ miles directly north of this exposure, on the south-
east side of a road, there is sandstone with thin pebble layers. There
seems to be a very low northerly dip of the rocks here, nearly horizontal.
The most easterly exposures occur west of Clarks Point, along the west
side of the road, as far north as Halls Creek. The strike on the average
is N.-S., the dip 20° W. About IJ miles northwest of Aliens Harbor
and 1 mile south of Potowomut River there is a large exposure north of a
schoolhouse at the road corner. The rock here is largely of the fine-grained,
252 GEOLOGY OF THE NAERAGAJSTSETT BASIN.
black, carbonaceous type, especially along the northwestern side of the
exposure, interstratified with which is coarser white sandstone. Both rocks
contain garnets, and the shaly rock is ottrelitic. Strike N. 23° E., dip
about 45° W.
Toward the western end of Potowomut Neck, near a residence north
of the road, are numerous exposures of sandstone with strike N. 50° E.,
dip 35° N., on the western end of the exposures. Toward the eastern end
of the neck a series of exposures extend from the Potowomut Rocks directly
southward nearly to the Potowomut River. The general trend of the rocks
is northeasterly, but it is evident that considerable irregular flexuring or
folding has taken place, so that the strikes are very irregular, and the dips are
both northerly and southerly, according to the particular locality observed.
While therefore unsatisfactory for purposes of stratigraphy, these exposures
are still worthy of close examination, because they show some very inter-
esting phenomena connected with the shearing of these rocks more or less
perpendicular to the bedding and the consequent interpenetration of the
frayed surfaces of the adjoining layers. The more carbonaceous layers in
the exposures west of the house -north of the road show garnets and other
minerals, the products of metamorphism ; one of these minerals occurring
in the rock is columnar, black, with frayed expanded ends. While a large
part of the rock exposures are coarse white sandstone or finer-grained black
shaly rocks, as in the rest of the series described in this area and south-
ward, yet there is a very large exposure, west of the buildings north of the
road, of a greenish shaly rock, spotted with the stained marks caused by
the weathering of some pyritiferous mineral, which is very unusual in the
series. The strike at the Potowomut Rocks seems to be N. 50° E., dip
apparently steep northwest.
WESTERN BORDER OF THE CARBOISTIFBROITS BASIIST, FROM EAST
GREEIS^VICH TO NATICK A:N^D NORTHWARD INTO CRANSTON.
The present western border of the Carboniferous basin of the Narra-
gansett region extends from East Greenwich southwesterly, west of Davis-
ville and Wickford Junction. At East Greenwich the pre-Carboniferous
rocks form the steep hillside above the town. At a road corner near the
top of the hill, in a line almost directly west of the Potowonuit Rocks,
these more ancient rocks are well exposed in a quarry. The rock here is
EAST GKEENWIOH TO NATICK. 253
very fine grained and white, with minute black specks. The cleavage
planes lie E.-W., dip low northerly. The western border of the Car-
boniferous basin probably follows the steep hillside from East Greenwich
to Coweset, and thence for some distance the northern side of Drum Rock
Hill. The presence of (1) granite exposures near the southeastern end of
the hill, half a mile west of the southern end of Grortons Pond; (2) a fine
exposure of the quartzite and schist series at the northern end of the same
hill, hardly a sixth of a mile east of Natick; (3) an exposure of the same
series on the western side of the hill, a quarter of a mile south of the last
locality, and (4) a series of exposures southwest of the third locality, along
the road leading directly south from Natick, in order — quartzite, then gran-
ite, then quartzite again — tends to show that the present western border
passes only a quarter of a mile west of Gortons Pond and thence north-
westerly to Natick.^
From Natick northward the basal rocks of the Carboniferous series
form the steep hill front for a distance of at least 2 J miles, while the eastern
line of outcrops of the pre-Carboniferous series can be traced far northward
into Cumberland.
The greatest interest in this border line, however, centers in the com-
paratively small stretch of 2^ miles from Natick northward, since here the
Carboniferous beds can be seen resting on the pre-Carboniferous series, the
basal beds containing very many angular fragments and rounded pebbles
derived from the older rocks, the material of these pebbles varying with
the character of the underlying rocks immediately adjoining. All grada-
tions may be seen, from the most angular fragments to well-rounded
pebbles.
The quartzite-schist series is well exposed along the north side of Bald
Hill northward as far as Natick, especially west of the town. Near the
center of Natick a road leads up the very steep hill west of the town. Just
north of the beginning of this road is a church, below which the quartzite
series is exposed. Ascending the road for a distance of perhaps 100 feet,
turning northerly into a group of houses, the observer discovers a fine
exposure of the Carboniferous base resting against the quartzite on the west.
' The evidence leads me to believe that the margin of the Carbonilerous field originally lay much
farther to the west. It is likely, indeed, that it may have merged with what is now the Worcester
li.isiu.— N. S. S.
254 GEOLOGY OF THE NAREAGANSETT BASIN.
The bed is rather bluish and dark in color, and contains very angular
and rather separated fragments of white quartzite, producing a striking
effect on account of the differences of color and the consequent distinctness
of outline of the fragments. This effect is heightened by the comparative
rarity of the bits. From this cluster of houses a short footpath leads
west up the steep hill to the house of Mr. Alexander McTeer. Northeast
of his house an equally striking exposure is met, the rock here being a
great mass of very distinctly outlined, very numerous angular fragments
of quartzite embedded in a slightly darker cement. From this point the
basal Carboniferous conglomerate forms the northeastern face of the hill,
the underlying quartzites being often well exposed just southwest of the
brow of the hill. It often requires close observation to distinguish quartz-
ites, where brecciated in situ, from the overlying breccia- conglomerate
series which forms the base of the Carboniferous. Southwest of the road
corner, where the present western border of the Carboniferous area makes
a sharp curve toward the east of north, the underlying beds are of a pecu-
liar greenish rock, often seen northward, as far north as the Cumberland
district, where it is copper bearing. The quartziferous basal layer with
angular fragments lies west of the road. At the edge of the roadbed
southwest of the road corner mentioned, on the east side, the overlying
carbonaceous black shaly rock is exposed, dipping under a coarse sandstone.
Strike N„ 30° W., dip, as inight be expected, 50° E. The presence of this
carbonaceous bed so near the border of the Carboniferous basin, and so
near the base, is very interesting, especially since the basal bed is so
conglomeratic.
The basal quartzitic conglomerate beds are well exposed west of the
road north of the road comer already mentioned. They rest here on
granite. There evidently is a sharp curve in the border line. The expo-
sures can be followed back of the house tln-ough the woods for a sixth of
a mile. At one exposure along the roadside the basal bed contains granite
pebbles over a foot in diameter. After this the basal series must be fol-
lowed along the east side of the road through the woods. Here the rocks
are a coarse quartzitic sandstone. Pebbles are not numerous, and as a
rule they are rather small. The sandstone can be readily followed through
the woods to a fine waterfall, the existence of which would not be suspected
from the road. Here it is well exposed; strike N. 40° E., dip 60° E. Thin
FROM NATICK NOllTHWARD. 255
carbonaceous bands assist in showing the bedding. The series can be
traced into the open field northward. Here it rested formerly upon granite
and schistose rocks. An exposure in the open district, just east of the road,
isolated from the rest, shows among the pebbles also one derived from the
gneissoid schist, an interesting occurrence, since, in spite of the abundance
of the schistose rock in the vicinity of the basal sandstone and conglom-
erate series, pebbles from the schist are rarely found. The schist does not
seem to have furnished many pebbles, but broke up into a fine grit on
aerial degradation and furnished part of the finer material of the overlying
series. The granites also must have been considerably decayed. The
alteration products of the feldspars drifted farther away from the land,
but the quartzitic material remained nearer the shore to form the cement
of the basal conglomerates and the overlying arkose and sandstones; but
pebbles of granite are by no means uncommon, although quartzite, on
account of its greater durability, formed the predominating pebbles of the
basal conglomerates.
The basal series of arkoses and sandstones, with scattered pebbles, may
be traced east of the road to a point about a mile north of the road corner,
where the sharp bend in the western border of the Carboniferous area occurs.
Here the basal beds rest upon a varied group of rocks — gneissoid schists, a
peculiar greenish rock of the type found in Cumberland, and granite. North
of this point the basal series crosses the road and follows it along its west-
ern side, resting upon granite as far as the next road corner northward. A
house stands east of the road near the point where the basal series crosses
the way. A short distance north the road crosses a stream. Up the stream
westward, in the woods, the basal series, only moderately conglomeratic
with granite pebbles, may be seen well exposed. A quarter of a mile from
the northern road corner the very steep hillside is formed by white coarse
sandstone, with layers of small pebbles and occasional scattered angular
pebbles, some of them as much as 9 inches in diameter; some of the latter
are granite. The underlying rock is granite. From this point the basal
series can be followed to a short distance south of the road corner, behind
a barn, where, in an open field, there is a fine exposure of the series
overlying the granite; conglomerate layers are frequent, often with large
pebbles, some of these of granite, the greater part of quartzite. From this
point the basal series passes northerly to a point west of the road corner, a
256 GEOLOGY OF THE NAERAGANSETT BASIN.
third of a mile distant. This exposure, along the western road, is very
interesting on account of the extreme lengthening and flattening which
many of the pebbles have undergone in consequence of shearing. The
pebbles consist of quartzite and granite. Those of larger size, embedded
in the softer cement, have been less sheared and can be more readily recog-
nized. The basal conglomerates continue to be shown along the western
side of the road to Knightsville, resting toward the south upon granite,
and farther north upon schists. Where the basal series fails to be exposed,
the western border of the Carboniferous area can still be recognized by the
steep hillsides formed by the older pre-Carboniferous rocks.^
ROCKS EAST OF THE WESTERN BORDER OF THE CARBO^^^IFEROUS
AREA IN WARWICK AISTD SOUTHERN CRANSTON.
The basal series of rocks are quartzitic sandstones of white color.
Overlying them are bluish sandstones and coaly shales. The coaly shale
east of the great bend in the western border of the Carboniferous area
northwest of Natick has already been mentioned. At the northern end of
the village, along a connecting road west of the river, blue sandstone with
darker courses, and a few conglomerate layers with small pebbles, are well
exposed. Strike N.-S., dip 45° E. A sharp change in the strike must
take place in Natick, as already indicated in connection with the description
of the border line.
Along the road from western Pontiac northward a number of expo-
sm-es occur. They indicate the presence of bluish sandstone, with small
pebbles, and bluish-black ottrelitic shaly rock along the western side of the
hill east of the New York, New Haven and Hartford Railroad. The strike is
northerly and the dip 10° E. The entire hill and the valley on the west
is probably underlain by an alternating series of blue sandstones, often with
conglomeratic layers and bluish-black or black ottrelitic shales. Coaly beds
are common on the east side of this line of hills, and were formerly mined
fai'ther northward, at the well-known mines northeast of the Reform School
on Sockanosset Hill, on the east side of Rocky Hill, which geologically
is a continuation of Sockanosset Hill, and still farther northward in the
Valley Falls district. This series of coaly rocks not far above the base of
' In my opinion this cliff is not an old shore escarpment, bnt is due to the deformation of the old
floor of the basin and the subsequent erosion of the soft beds which lie against it. — N. S. S.
WAEWIGK AND SOUTHERN CRANSTON. 257
the Carboniferous, extending along the western border of the Carboniferous
field, often presenting workable coals, was well recognized by early investi-
gators of this district, many of the mines dating back more than fifty years,
though all save one, that at Valley Falls, are now totally abandoned.
The most southern exposure on the east side of Sockanosset Hill is
half a mile south of the State almshouse, near the railroad. The medium-
grained sandstone is bluish; the coarser, whitish. Quartz pebbles up to
1^ inches in diameter occur in the conglomeratic layers. The series dips
10° NE. In front of the almshouse are black ottrelitic shales. Toward
the northeastern side of the building, and thence for a rather long distance
through the grounds, more sandy bluish sandstones, occasionally conglom-
eratic, occur, merging into fine-grained rocks, and these into greenish and
bluish shales, in part ottrelitic. The strike of the series is north-south, car-
rying the rocks east of the Reform School. The dip is 20° E. The finer-
grained rocks and shales rather predominate in this series, and may also be
seen near the almshouse, east of the road. In the vicinity of the Reform
School and of the reservoir, exposures of bluish sandstone and ottrelitic
shales occur. The coaly beds, including the workable coals, occur half-
way down the eastern hillside and thence down into the valley region.
The strike of the rocks is north-south, the dip low east — usually 20° E. —
except toward the mine, where the dip, according to the miners, increases
to about 50° E. If this is true, it is a local flexure, the dips eastward being
low again. The existence of such a flexui-e seems, however, to be supported
by indications northward, the dip at Wayland Station, on the northwest
side of Sockanosset Hill, being 20° to 30° E., while on the eastern side of
Rocky Hill it is 40° to 70° E.
Eastward of the Pawtuxet River, however, the exposures show low
dips again. Along the railroad north of Hills Grove Station, black, often
coaly, shales lie almost horizontal. North of the road corner east of the
station a quarry shows abundant sandstone with a northward dip of about
20°. A third of a mile north of the station, west of the railroad, abundant
sandstone with conglomeratic layers shows a northeastward dip of 20°. The
sandstone contains steins of calamites, longitudinally coarsely corrugated
stems, undeterminable flattened stems, and leaf-like impressions, 1 or 2
inches wide and 15 to 30 inches long. Similar forms may be recognized
MON XXXIII 17
258 GEOLOGY OF THE NARRAGANSETT BASIN.
ill the Silver Spring region. A quarter of a mile southwest of Norwood
Station, west of the railroad crossing, numerous exposures of sandstone
having a low easterly dip occur.
WARWICK ISTBCK.
Eastward of Hills Grrove and Norwood stations there are no exposures
in Warwick until Warwick Neck is reached. In the railway cut west of
the main road passing along the length of the neck, black carbonaceous
shales and some sandstone courses dip in a northerly direction. West of
the same road, a quarter of a mile south of the highest point of the neck,
sandstone is exposed. East of the highest point of the neck the hill-
sides, sloping steeply to the shore, show frequent exposures of sandstone
dipping at an angle of about 40° E. Nearer the foot of the hill carbona-
ceous dark shales make their appearance. The sandstone continues to be
well exposed for about a fifth of a mile southward. Northeast of these
exposures, north of a small pond where the shore turns northeastward to
Rocky Point, black shales dip low eastward. Corresponding bluish-black
shales and fine-grained sandstones are found a quarter of a mile north-
ward, along the road to Bay Side. There occur in succession, eastward:
Sandstone, forming the south end of the high ridge east of the road last
mentioned; conglomerate, forming the middle and northern part of this
ridge; sandstone, exposed at the northeast of the northern end of the ridge
and on the western side of the main hill occupied by the Rocky Point
booths; conglomerate, forming the eastern part of this hill, and a solitary
exposure farther northward, and then various sandstone layers as far east
as the point, the intervening courses not being seen, being probably some
softer shale. The strikes of the exposures at Rocky Point are N. 10° W.,
dip 20° E. Many of the pebbles in the conglomerates at Rocky Point are
of considerable size.
A short distance north of Sand Point, on the neck, sandstone and con-
glomerate are exposed dipping to,vard the northwest. At the southern end
of Warwick Neck, near the light-house, and for a short distance westward,
black carbonaceous shales and some sandstones are exposed dipping in gen-
eral northward, but suggesting in places a sort of contortion of the rocks by
a force acting in an east-west direction.
CHAPTER IV.
THE NORTHERN SHORE OF THE BAY.
PROVIDENCK RIVER AISTD EASTWARD.
The geology of the area directly east of Warwick, on the eastern side
of Pi'ovidence River, in Barrington, is laot well disclosed by outcrops.
It will be remembered that the strike of the exposures west of Rocky
Point was a little west of north and the dip low east, about 20°. The
strike would carry these rocks a little west of Pawtuxet village. At the
mouth of the Pawtuxet River sandstone is exposed, and the neck upon
which a part of the village is built is apparently underlain by a similar
rock. This sandstone could easily belong to the Rocky Point series, if the
Rocky Point exposures be correlated with the exposures on the eastern side
of the river.
These eastern exposures extend from East Providence, north of
Watchemoket Cove, along the shore as far as a point directly west of
Riverside Station. This section is chiefly sandstone, although at certain
horizons conglomerate layers are abundant. In the region east of the
Pomham rocks a local syncline can be detected. Immediately east of this
syncline there are a number of exposures with westerly dip.
Half a mile east of the Pomham rocks there are three ridges in
obliquely overlapping order, fi-om south to north. The middle ridge shows
a westward dip of 30°. The middle and northern ridges contain considera-
ble conglomerate. The southern ridge consists chiefly of sandstone.
Isolated exposures occur north of the series of ridges. No perfectly
satisfactory stratification planes can be made out in the northern and
southern ridges. This leaves room, of course, for the supposition that east-
ward dips may occur in them and that we have here a series of closely
folded anticlines and synclines.
260 GEOLOGY OF THE NARRAGAXSETT BASIN.
The nearest rocks with well-defined dips are shown in a set of large
sandstone exposures a moderate distance east of the three ridges named.
These eastern sandstone exposures show an undoubted westward dip of
40° to 45°. This is indicated both by the presence of conglomeratic layers
and by the distribution of a larg-e number of plant stems. Owing to the
two distinct cases of westward dips east of the Pomham local syncline, one
in the middle ridge, the other in the sandstone quarried east of this ridge,
a general synclinal structure, of this region seems a possibility, although
the probability of a series of folds here must not be excluded.
With this possible structure in view, the conglomerates and sandstones
west of Rocky Point and east of the Pomham rocks are correlated as belong-
ing at least to the same general series, above the rocks found farther west-
ward in Warwick. In other words, these rocks are believed either to overlie
the Saunderstown sandstone series as a distinct superior formation or to form
the summit of that series.
If this be true, the sandstones and conglomerates east of the Provi-
dence River must dip southeastward on approaching Rumstick Neck, in
order to underlie the exposures south of that neck, if the shales of the latter
are to be correlated with the Aquidneck series. The exposures within the
writer's field are inadequate to settle this question.
EUMSTICK NECK.
The first exposures eastward of Providence River, in Barrington, occur
along the southeastern shore of Rumstick Neck. About a quarter of a mile
west of the southern end of the neck lies Long Ledge, made up of Carbon-
iferous sandstone with strike N.-S. and dip 30° E. A little southeast
the same sandstoiie is exposed in Riimstick Rock with strike of E.-W.
and dip 45° N. The sandstone here contains impressions of plant stems —
one like calamites, the others coarsely ridged. They are of the same
type as those found at Hills Grove, east of Providence River, north and
south of Silver Spring, in the quarry east of the range of three ledges,
northeast of Riverside, and elsewhere. On the shore itself is greenish shale
of the same type as that belonging to the shale series northward. It seems
to have a strike of N. 20° W., dip 30° E., and evidently overlies the sand-
stone of the ledges.
CARBONIFEROUS AREA OF BRISTOL NECK. 261
POPASQUASII NECK.
A long ridge of sandstone lies northwest of Ushers Cove, first trending
northward, then northeast, and then more northerly again. It is of bluish
color. No satisfactory strikes and dips could be determined, although the
exposure is large.
BRISTOL :N^ECK.
CARBONIFEROUS AREA.
The lowest Carboniferous exposures on the neck consist of coaly
black shales, opposite the Brothers and Deyers Rock, where the railway
begins to turn toward the southeast, leaving the shore. The strike seems
to be N. 10° W., dip 40° E. Species of Annularia and ferns occur in the
rock. The same black shales are found three-foiu-ths of a mile farther south-
east, in the railway cut, where the strike is northwest and the dip aiortheast.
Above this coaly shale, exposed along the shore a quarter of a mile north
of the Brothers, lies sandstone containing black shaly layers showing a
strike of about N. 10° W., dip 40° E. Northeast of these shore exposures,
east of the railroad, is a high ridge of bluish sandstone, whose strike and
dip can not be determined, although the dip is probably eastward and the
strike probably of such a character as to connect this exposure Avith a set
of sandstone exposures farther south. This set of sandstone exposures
begins on the hillside east of the Brothers and of the railroad. It strikes
at first about N. 20° W., dipjDing 20° E. In the exposures southeast of
this locality the strike becomes more and more nearly east-west until, in a
quarry just west of the Warren-Bristol road, it is about N. 85° W., with a
dip of 20° N., the strike becoming perhaps N. 80° E. just before reaching
the road.
Above this sandstone, toward the north, lies conglomerate. The most
conspicuous exposure is less than half a mile south of Jacobs Point, just
east of the railroad. The conglomerate liere has a thickness of at least 20
feet. Its dip is low eastward, as may be seen by sandstone layers near its
northern end. The pebbles are of sandstone and are often 6 to 10 inches
long. The other conglomerate exposiu-e lies 1,500 feet southward, indicat-
ing by its position relative to the other exposure a strike of N. 10° W. It
forms a small knoll in an open field. East of the region between these two
262 GEOLOGY OF THE NAREAGANSBTT BASIN.
conglomerate exposures lie g-reeii shales of the same type as those belong-
ing to the shale series southward. The green shales are exposed chiefly
along two low ridges, the first one-third of the distance from the line of
the conglomerates to the Warren-Bristol road, and the second about two-
thirds of that distance. No strike and dip could be determined. The
cleavage is mai'ked and the planes are numerous. Notwithstanding the
absence of definite stratification the dip is undoubtedly eastward, corre-
sj)onding to the dip and strike of the rocks below and above. The green
shales therefore here overlie a very coarse conglomerate, but the conglom-
erate seems to have had but a very limited extension. Overlying the bluish-
green sliale is a bluish sandstone bed, the lowest part of which is conglom-
eratic, the pebbles beiag of small size. The exposure occurs east of those
last mentioned, east of the Bristol-Warren road, and forms the summit of
the hill. The strike can not be well determined, but seems to be about
N. 45'^ W., dip 45° E. Eastward the sandstone becomes rapidly less coarse,
then very fine grained, and is finally overlain by the bluish shale which
forms the exposures over the remainder of the area of the neck north of
the pre-Carboniferous granite region. This shale is well exposed west of
the road half a mile farther northward, east of the road in the valley, and
along the entire western margin of the hill just beyond for half a mile
southward. It is also exposed near the summit and along the northern
and northeastern sides of this hill, which may be recognized by its height
of 120 feet, as indicated on the map. At the second angle of the road
toward the northeast of the hill the shale is very black and carbonaceous.
Farther eastward, east of another main north-south road, the greenish-blue
shale is again abundantly exposed directly east of the summit of the 120-
foot hill. The shale is also well exposed in quarries and on the hillside
less than a mile farther northward on the eastern side of the hill, near the
top. In all this area, excepting in the cases already described, the Carbon-
iferous is represented by the shale series, varying from bluish green to
g-reenish and bluish, sometimes dark blue and black.
GRANITE AREA.
Granite occupies the southern part of Bristol Neck. A coal bed was
once exposed in the western part of Bristol only a few feet above the
harbor. It was said to strike east of north and to dip about 48° W. The
GEANITE ON BRISTOL NECK. 263
coal was said to be of excellent quality/ Grranite is exposed at the north
end of Walkers Cove. Thence it occurs along all the more elevated streets
of the town. North of Bristol the outcrops extend for about a mile a little
east of north, and then east\'\'ard for another mile. The nature of the rock
which underlies the area along the shore east of the very large quartz
veins on the east side of Mount Hope, and thence northward at least for a
mile, is unknown, since there are no exposures. At Walkers Cove, and
nmnerous other points in the granite area, the granite is coarsely jDorphyritic,
containing phenocrysts of feldspar an inch and more in diameter. Still
more frequently it does not contain the feldspar phenocrysts. Gneissoid
structure, in consequence of shearing, is very common, the shearing having
been as a rule in the direction N. 30° to 40° W. This agrees fairly well with
the direction of shearing in some of the exposures south of Common Fence
Point, north of the railroad, on Aquidneck Island. A verj^ fine-grained
pinkish rock occurs in places, especially in the valley northwest of Mount
Hope. This is believed to be an aplitic rock. The western side of Mount
Hope is formed by granite. The summit and precipitous eastern side are
formed by quartz veins of gigantic proportions, varying from 40 to 80 feet
in width. Grranite abuts against these veins on the west, but no exposures
occur on the east. On the shore northwest of Mount Hope Point a black
schistose rock is included in the granite. Its structure is probably the
result of shearing in the granite.
This granite may have formed an island in the Carboniferous sea, but
no arkose is known to occur at any point on Warwick Neck, and no
contacts are exposed between the granite and any clastic rock. Moreover,
the Carboniferous shales nearest the granite area do not show either strike
or dip, and the cleavage is also discordant with the outline of the granite
area. There is, therefore, no evidence of the existence of the granite area
as an island in Carboniferous time, although, judging from the history of a
similar granite on Conanicut, south of Jamestown, it is extremely probable
that it did so exist. Moreover, the granite of the Bristol Neck area and the
pre-Carboniferous granite along the east side of Taunton and Sakonnet
rivers show features so similar as to make it very probable that they
together constitute a geological unit.
' This mine has been filled up. Specimens of coal shown me were uf the same nature as that
from the Portsmouth mine. — N. S. S.
264 GEOLOGY OF THE NAERAGANSETT BASIN.
WAEREX IS^ECK.
About a mile north of Chases Cove, on Kickamuit River, the shore
line is deeplj'' indented and a valley extends thence northward for about a
third of a mile. West of this valley are abundant exposures of conglom-
erate, forming two hills over 60 feet high, the pebbles being rather large,
often 1 foot in length. There are very few interbedded sandstones, and
these lie almost horizontal or dip slightly eastward. The northern hill lies
southwest of the angle of one of the main roads of the neck. Northeast
of this angle a low ridge of conglomerate in the open fields continues the
exposures, increasing in elevation northward on entering the woodland.
Two-fifths of a mile northeast of this ridge, along the railroad, the con-
glomerate is exposed again, showing a strike of N. 30° W., dip 45° E.
Hardly a quarter of a mile eastward the conglomerate has a strike of N.
20° W., dip 30° E. Between these two exposures southward, in the fields,
occur others with approximately the same strike and dip. Farther eastward,
however, the fairly abundant exposures along the south side of the railroad
show, eastward, first, a northeast strike and a western dip, changing
rapidly to an almost east-west strike and a northward dip of perhajjs 20°
to 30°.
CONGLOMERATES A:N^D SHALES OF SWAKSEA AND WARREN, NORTH
OF THE NECKS.
The road from Coles Station to Luthers Corner leads first northward,
then eastward, and tben northward again. Just south of the second angle
of the road, along the shore, the conglomerate has a strike of about N. 60° E.,
dip low northward. Northward along the west side of the road ai-e several
exposures, the most southern of which has a strike of about N. 70° E., dip
about 50° N., the strikes farther north being also decidedly eastward and
the dips north. East of these exposures a road leads eastward to Fall River.
Where it crosses Coles River there are exposures on both banks. Exposures
also border both sides of the river for about a quarter of a mile northward;
and southward, below the bridge, exposures are found in the channel and
on the west bank. The strike for all of these exposures is about N. 45° E.,
dip 20° NW. Along the road leading from the western side of the
bridge northward exposures are abundant on both sides of the road, show-
SWANSEA AND WAREEN. 265
ing in general a northeast strike and a northwestern clip. One of the more
northern exposures, before reaching the 20-foot contour line, indicating a
valley entering the hillside from the east, shows a strike of N. 60° E., dip
45° NW. Continuing on this road northward, and tlien following the
main road toward Swansea village, there are abundant exposures of the
conglomerate south of the road, not far beyond the mill pond. Here
the strike is about N. 45° E., dip 50° NW. About a third of a mile east-
ward, at some distance south of the road, the strike is about N. 50° E.,
the dip northwest. The northwesterly dip is shown by the conglomerate
exposures at various points north of Swansea \dllage. The northeastern
strike and northwestern dip is also shown by the conglomerate exposures
which, beginning on the western side of the pond southwest of the village,
reappear on the eastern side, and are exposed again before reaching the
main street of the village. Following the road east from Swansea callage,
and taking the first road toward the north, exposures are found again three
quarters of a mile northward, bordering the road on the west. The same
strikes and dips can still be recognized, continuing thence northeastward to
Taunton River.
The general northeast strikes and northwest dips from the first exposure
here described, northeast of Coles Station, along Coles Eiver, throuo-h
Swansea Aallage, show conclusively that these coarse conglomerates overlie
the sandstones and shales farther south and east.
West of the exposures just described, from Coles Station as far as the
mill pond, halfwa}^ between Luthers Corner and Swansea, the conglomer-
ates dip toward the east, showing a synclinal structure over this area. The
easterly and northeasterly dips along the railroad, half a mile west of Coles
Station, have already been mentioned. A little west of north of Coles
Station, directly west of the first strong bend of the road already described,
conglomerate is exposed at the margin of the woods, with a strike of about
N. 65° W., dip about 30° NE. The conglomerate is here overlain by
sandstone merging into a fine-grained shaly rock. Northeastward, in the
fields, the conglomerate strikes N. 15° W., and dips east. West of Luthers
Corner, for a rather long distance west of the road leading north from
Coles Station, are a considerable number of exposures, most abundant
north and northwest of the corner. Their strike is in general north-south,
dip eastward, often very low. Half a mile north of the bridge across Coles
266 GEOLOGY OF THE NAERAGANSETT BASIN.
River, west of the road, and uortli of tlie 20-foot-contour valley already
noted, are a number of exj)osures showing in general a strike of about
N. 20° E., dij) 45° E. Overlying some of the more southeastern of these
exposures, on the west side of the road, is a bluish shale. The conglomerate
is also exposed east of the road. A third of a mile west of the mill pond a
long exposure beside the road west of the bend shows a strike of N. 25° E.,
dip 30° SE. Overlying the conglomerate is a greenish shale. Just west
of the mill pond the strike is N. 70° E., and the dip almost veiiical.
Northeast of the mill pond the conglomerate exposures northwest of Levins
Brook do not vary far from the horizontal, and the synclinal structure can
no longer be followed.
The detection of the synclinal structure between Coles Station and
the mill pond, and the more horizontal position of the rocks to the north-
ward, is of some assistance in establishing the continuity of this more
eastern conglomerate, whose stratigrapliical equivalents with the conglom-
erates in Warren, north of Bristol Neck, and in adjacent parts of Swansea,
can be easily determined. Indirectly also it is serviceable in determining
the position of the bluish-green shale series of Bristol Neck, as the following-
notes may show :
The wide distribution of the bluish-green shale series in Bristol Neck
has already been noted. From Warren, eastward along the first road lead-
ing north, passing east of Belchers Cove and Warren River, bluish shale
occurs east of the road a third of a mile south of Kings Rock. Sandstone
occurs Avest of the road, and is also exposed in the northeast angle of the
first road leading toward the east. At the latter locality a few stray peb-
bles of large size are embedded in the sandstone. At Kings Rock, west
of the road, on the Massachusetts-Rhode Island boundary line, and also
northeastward, east of the road, are large exposures of the bluish shale.
The strike of these rocks is about N. 15° E. A mile south of Kings
Rock a road leads off eastward to Luthers Corner. Less than half a mile
along this road another branches off northward. South of this point a
considerable area is covered by bluish and greenish shales, frequently
exposed. These shales are also exposed on the eastern side of the hill, east
of the road, at several points from a quarter of a mile north of the road
corner to half a mile northward, and they are found again a mile north of
the road corner, a quarter of a mile east of the road, near the State boundary
GAEDENBRS NECK. 267
line. This. set of exposures indicates a strike of N. 15° E. East of the
last exposure is coarse sandstone. Toward the northwest and north extend
several ridges of sandstone and conglomerate, the most eastern of which
can be followed for a mile, as far as the next east-west road. The strike
is N. 15° E., dip always eastward, often as low as 20°. Conglomerate
and sandstone also occur north of a house some distance east of the road, a
quarter of a mile south of the State boundar}^ line. A mile northeast of
Kings Rock numerous exposures border the roads eastward and northward.
They consist chiefly of sandstone and some conglomerate, dipping eastward,
but they also contain greenish shaly laj^ers toward the north end of the
series of exposures, where the strike seems to be more nearly east-west and
the dip southward.
A third range of bluish shales forms a ridge bearing N. 15° E., both
north and south of the road to Luthers Corner, already mentioned. East-
ward from this ridge, three-quarters of a mile northward along the first
road on the east side, conglomerate is exposed; strike N.-S., dip 70° E.
Greenish shale miderlies it on the west.
The various exposures north of Bristol Neck, just described, seem to
indicate that the bluish-green shales underlie the great mass of conglom-
erates. These conglomerates are the coarse conglomerates on Aquidneck
Island and occur at a considerable distance above the lowest beds of the
Carboniferous exposed along the eastern shore line of the basin, from
Steep Brook to Tiverton.
GARDENERS NECK,
The eastern line of outcrops of the coarse conglomerate runs through
Swansea village, in a northeasterly direction. Beneath these conglomerates,
on the east, occurs a series of shales and sandstones. South of the pond
southwest of Swansea village, in the bed of the creek which forms its
outlet, and in the field between the creek and the road, there are several
exposures, chiefly sandstone, but also some more shaly courses, dark
blue in color. Southward rather more than a mile, on the road to South
Swansea, an exposure of coaly shale occurs south of the road leading
eastward to Fall River. This exposure occurs in a digging- on the eastern
side of the Neck, near the top of the hill. Half a mile farther south, near
the base of the hill, toward Lees River, a shaly sandstone or slaty rock
268 GEOLOGY OF THE NAERAGAlSrSETT BASIN.
occiTi'S. Its strike is probably N. 40° to 45° E.; this at least is the direction
of the line of outcrop. The color is bluish black, or quite black where
shaly. This more southern set of exposures occurs stratig-raphically
beneath the coaly shale lying farther north.
BRAYTONS POIISTT AND NORTHWARD.
On the northwestern side of the point black coaly shales are exposed.
These continue southward as far as the middle of the west shore, where
sandstone is frequentl}^ interbedded. The strike farther north seems to be
N. 50° E., but southward it varies to N. 70° E., and becomes N. 30° E., dip
70° W., near the middle of the west shore. The black shales here con-
tain Annularia longifolia and fern impressions. Farther southward black
coaly shales continue to be exposed as far as the southern end of the point
and its southeastern side. These more southern exposures show, a strike of
N. 50° E., dip 80° W., or other variable lower angles. The bedding here is
not often well shown.
SEWAMMOCK KECK.
A mile and a quarter west of Brayton, on the road from Fall River,
crossing the neck, on the western side of the hill, a rather coarse sandstone
is well exposed. Its real strike and dip could not be determined, the
apparent bedding being probably only cleavage. Similar gra}^ sandstone is
exposed half a mile west of Pottersville, north of the road. This sandstone
probably underlies the coaly shales of Braytons Point.
CHAPTER V.
THE EASTERN SHORE OF THE BAY.
STEEP BROOK.
Pre-Carboniferous granite forms the steep slopes of the hilly country-
bordering Taunton River on the east. The western line of outcrop of tlie
granite extends from Steep Brook northward as far as the point where the
Myrick branch of the railroad leaves the main line. The line of outcrop
of the granite then turns abruptly eastward and follows the southern side of
the railroad as far as Washington Mountain. At Steep Brook the granite
is well exposed along the sides and in tlie bed of the brook. The contact
with the Carboniferous rocks is not exposed. The lowest exposure of clastic
rock consists of conglomerate, strike N. 45° E., dip 30° W. Toward the
north, overlying the conglomerate, is sandstone, with a dip of 40° W.
Thirty feet west of the conglomerate there was not long ago exposed a
narrow coal seam, with coaly slate containing fern impressions. Its strike
was N. 15° E., dip 20° W. West of the coaly layer occurs a considerable
thickness of arkose, in some places scarcely showing bedding, in others
indicating the planes of bedding by color banding caused by more carbo-
naceous material in certain thin layers. A little of the arkose material
exists beneath the coaly layer. The arkose consists chiefly of quartz,
derived from decayed granite. The quartz grains as a rule are not rounded.
The granite which furnished the constituents of the arkose must have been
reduced to a mass of loose material by aerial decomposition, so that the
quartz grains were readily washed away in order to form the arkose, while
the feldspathic material formed interbedded layers of the impure kaolin,
which was once quarried by the owner of the premises for shipment to
pottery works. The absence of the arkose and clay material near the base
of the series here is noteworthy. Still more important is the conglomerate
layer near the base, for the conglomerate, although so near the granite
area, does not consist of granite pebbles, but of quartzitic pebbles, often 3
269
270 GEOLOGY OF THE NARRAGANSETT BASIN.
iuches long, similar in character to the pebbles in the Dighton conglomerate.
The granite from which the arkose and kaolin were derived was too decayed
to furnish pebbles, but the quartzitic rocks withstood weathering sufficiently
to furnish good pebbles to the basal conglomerates, in spite of probably
long transportation.
FALL RIVER.
A still more interesting exposure occurs in Fall River, in Annawan
street, halfway down the hillside, behind some mills. The eastern border
of the present Carboniferous area extends from Steep Brook along the
escarpment bordering Taunton River to this locality in Fall River, with a
trend of about N. 32° E.; southward to Townsend Hill its trend is N, 40° E.'
In the angle a considerable exposure of the overlying Carboniferous rocks
is preserved. Behind the mill on Annawan street the arkose rests directly
upon the granite or is separated from it only by a thin course of coaly
shale. The contact is well shown. Arkose layers, composed chiefly of
angular quartz grains derived from the granite, alternate with coaly shale
layers. Northward toward the railway tunnel under the next street, the
alternation of arkose and coaly shale layers continues, the arkose changing
to a gritty sandstone; the coaly slate then forms a considerable exposure,
overlying the arkoses, and constituting the steep wall of the hillside as far
as the railway track; strike N. 50° E., dip 40° W.; farther south, strike
N. 30° E. Fern impressions occur in the shales. West of the railway track
occurs a gritty sandstone.
TOWNSEND HILL.
Two and three-fourths miles southwest of the exposure in Fall River
occurs the exposure on the west side of Townsend Hill. Granite forms
the hillside down to the 100-foot contour. Below, where a small bench
occurs, forming a northerly projection on the hillside, the arkose is exposed.
The actual contact with the underlying granite is not seen, the stratigraphic
interval being about 5 feet.
' The existing escarpment seems to me to be due to tlie deformation of tlie granite formation of
the basin and the subsequent removal of the softer stratified beds. If the Carboniferous shore lay
along this line, it was there but for a short time during the progressive overlapping of the accumu-
lating basal sediment. — N. S. S.
EASTERN SHOEE OF THE BAY. 271
TI^TERTOiS^.
The granite escarpment trends N. 30° E. as far as the western side of
Pocasset Hill, changing thence to N. 13° E. as far as the exposures north-
east of the railroad bridge. The lowest exposures of the Carboniferous
series occur in the quarry on the hillside. Here the prevailing rock is
arkose. The lowest part of this arkose, stratigraphically, occurs very near
the granite. Nearer the lower end of the quarry blackish shale occurs.
Tracing the exposures northward, a whitish, fine-grained, quartzitic rock,
very much like the rock exposed west of East Greenwich, occurs between
the Carboniferous rock and the granite, and is evidently pre-Carboniferous.
Along the railroad tracks, overlying the grits, occur abundant exposures of
conglomerate, composed chiefly of quartzose pebbles, some of them 8
inches long. No granite pebbles were seen. Coarse sandstones are inter-
bedded. The abundance of quartzose pebbles and the absence of granite
pebbles here is paralleled at Steep Brook. The more northern exposures
along the railroad have a strike N.-S. and dip 30° W. At the quarry the
strike becomes N. 35° E., the dip 40° W.
The next exposure of Carboniferous rocks occurs a mile and tliree-
quarters farther south, east of the northern end of Nannaquacket Pond.
At the northern end of -the pond the granite appears at the shore. But a
short distance farther south, on the hillside, the arkose is seen resting upon
the granite. A little coaly shale is interbedded with the arkose. Strike
N. 20° W., dip 45° W. Farther south the granite comes down to the road-
side. It is evident that the contact line between the Carboniferous rocks
and the granite must turn westward where Sin and Flesh Bi-ook enters the
pond. Granite occurs also along the northern side of Sin and Flesh Brook
near the pond, and also directly north of the pond, on the north side of the
road skirting the same. This would require a still farther westward trend
of the shore line.
Returning to the arkose exposure, the granite comes down to the road
near the fork of the way. North of the road, after passing the turn toward
the east, the arkose occurs again high up on the hillside, but associated with
considerable coaly shale. The strike here is N. 85° W., dip 65° to 70° S.
If the observer crosses the road at its bend, he will find an excellent exposure
in the open area on the hillside, southwest of the wooded summit. Here the
272 GEOLOGY OF THE >f AEEAGANSETT BASI^.
contact between tlie granite and the overlying Carboniferous rocks is again
well shown. The clastic rocks consist of a series of interbedded arkoses and
coaly shales, soraetimes one, sometimes the other kind of rock forming the
contact with the granite. The contact line is usually very distinct. The
same strike of N. 85° W., dip 60° S., is shown. The arkose and granite con-
tact can be followed as far as the creek entering Nannaquacket Pond from the
east. From the pond southward it evidently takes a more southerly course,
following the eastern side of the low land west of the granite hill, and then
following the valley of a small brook as far as Tiverton Four Corners.
North of Nannaquacket Pond normal granite occurs, as already de-
scribed. Still farther north a white fine-grained micaceous schist is
exposed over a considerable area, until farther northward the granite
appears again. The whitish micaceous schist may be followed eastward
across the north-south road. It forms the southern end of the hill north
of Sin and Flesh Brook and occurs along the northern branch of the
stream. It also occurs south of the brook, the line of contact with the
granite crossing south of the ice-house pond. West of this pond, along
the road, the schist has been brecciated so as to resemble at first sight a
cong'lomerate. In places this rock looks very much like a very fine-grained
aplite made schistose by shearing. East of the ice house, between the
branches of the brook and also south of the south branch, a greenish schist,
often containing a dark-greenish hornblendic-looking mineral, is common.
The granite nortli of this schist area not uncommonly also shows the effect
of shearing and has a sort of gneissoid structure. The schist area has not
been thoroughly studied. This will later, however, be desirable in order
to learn whether the present eastern border of the Carboniferous area north
of Nannaquacket Pond is due to the topography of the early Carboniferous
sea bottom or is a result of subsequent sliding of the more northern pre-
Carboniferous granite to the westward.
GOULD ISLAND.
The main mass of the island consists of a very fine-grained rock, vary-
ing in color. In some places it is white, with minute black specks, prob-
ably biotite; in others it is light bluish gray or dark blue; in still others it
is gray, but contains many light-colored blotches. This rock has been
extensively brecciated by a shearing action which took place in a direction
GRANITE OP NORTHEEN AQUIDNECK. 273
about N.-S., or a little west of north. In consequence of the breccia-
tion the rock often has a decidedly conglomeratic appearance. Where
shearing has taken place the pebble-like fragments usually remain light in
color and the cementing material is darker. In other places the fragments
are very dark in color and seem macroscopically to be full of hornblende
and black mica. These dark fragments resemble closely the so-called dark
or hornblendic schists of the Sin and Flesh Brook section, while the light-
colored rocks resemble the lighter so-called quartzitic schists of that section.
A pinkish aplite cuts the rock near the southeast end of Gould Island in
the form of narrow dikes.
GRAKITE AREA OF THE KORTHEAST EKD OF AQUIDNECK
ISLANB.
Whitish granite occurs along the southern margin of Hummock Point,
and reddish granite is found along the east shore farther north. A pinkish
aplite cuts the same. Whitish granite forms a hill extending north of
Hummock Point as far as the railroad. The granite is frequently sheared
in a north-south direction, the result varying from a gneissoid granite
to a black mica-schist. Half a mile north of the railroad another set of
ridges begins, extending northward. It consists of whitish granite, sheared
in a direction west of north, often N. 20° W. One result of the shearing
is again a gneissoid structure, varying to a black mica-schist. Associated
with the granite toward the middle and northward is the fine-grained
quartzitic rock already described as occurring with the granite northeast
of the railroad bridge at Tiverton, and also as occurring in the Sin and
Flesh Brook exposures. Some of the Gould Island rock is also very
similar in character to the whitish rock at the northeast end of Aquidneck
Island, the whiter rock being probably identical in the two places. At
Common Fence Point occurs a reddish granite, not gneissoid.
The rocks exposed from Gould Island to Common Fence Point are
evidently pre-Carboniferous, and belong to the same series as the Sin and
Flesh Brook exposures, and that northeast of the Tiverton railroad bridge
on the hillside. The Carboniferous exposures on the hillside northeast of
Tiverton are noteworthy, suggesting that the eastern border of the Carbon-
iferous area extends southward toward the stone bridge. Possibly this
MON XXXIII 18
274 GEOLOGY OF THE NAEEAGANSETT BASIN.
border passes southward from the stone bridg-e, rounds the granites and
schists north of Nannaquacket Point, and then continues southward, east of
the pond. In that case the pre-Carboniferous range of exposures between
Gould Island and Common Fence Point miist have been brought to their
present position hj means of a fault bringing up these rocks from below.
At least there is no evidence that the Gould Island-Common Fence Point
range of exposures formed an island in the Carboniferous seas.
This explanation makes it unnecessary to hypothesize any connection
between the Common Fence Point range of granites and the Bristol Neck
granite area above the water surface in Cai'boniferous times.
EASTEKK BORDER OF THE CARBOXIEEROITS BASI?^ SOUTH OF
TIVERTOX FOUR CORKERS.
Half a mile south <_^f Tiverton Four Corners granite is exposed on the
northwest side of the hill, south of the brook entering Nonquit Pond from
the east. The granite continues to be exposed southward for a short dis-
tance, when greenish rock, having the appearance of a very fine-grained
sandstone, occurs. Its schistosity is N. 40° E., dip 45° SE., and there is a
probability that this should be taken as the strike and dip of the bedding.
This rock is exposed along the apparent strike at a number of places on the
northwest side of the hill. A quarter of a mile southeast, along the road-
side, the granite is abundantly exposed. The granite has been sheared so
as to present a pseudo-gneissoid structure with a northeasterly strike. The
granite and the fine-grained rock are pre-Carboniferous. The eastern border
of the Carboniferous area probably extends from Tiverton Four Corners
east of Nonquit Pond and Avest of the granite hill southward.
The granite is well exposed along the southern end of the hill north-
east of Tiverton Four Corners, almost east of the church north of Tiverton.
On the east side of Borden Brook the granite has been considerably sheared
in a direction about N. 30° E. The granite of this region contains in
places abundant phenocrysts of feldspar from 1 to 2 inches in diameter, and
these have been sheared to a lenticular form, producing a sort of augen-
gneiss. Where the shearing was more marked the black mica increased in
quantity. Extreme shearing reduced the granite in places to a biotitic
schist, whose real character it is not possible to recognize in the case of
every exposure. Gradations from one into the other can, however, be found.
JSrONQUIT POND TO WINDMILL HILL. 275
The hill east and north of Pachet Brook also shows abundant granite
exposures along the southern and eastern sides of the elevation. On the
southeastern side it includes, in several places, large fragments of rock,
ha\ang in some places the structure of a biotitic fine-grained schist
of blackish color, in others that of a ver}^ fine-grained whitish rock,
mottled, when broken across the schistosity, with blackish specks caused
hj biotite flakes. These included schist masses are distributed along a
line N. 30° E. in an irregular manner. They present the same strike in
their schistosity, and dip about 60° to 70° E. It would seem, therefore,
that they once formed a connected series in this region. It would be
interesting to learn whether these schists bear any close relation to the
Little Compton shales farther south, but the}' probably preceded them.
The granite near these schists is often porphyritic with large phenocrj'sts
of feldspar. This is also true of the nearest exposure of granite east of the '
north branch of the brook. Farther eastward the granite is of the ordinary
type. Southward, west of the south branch of the brook, at various points
near the road, a whitish granite is exposed. Farther westward there is no
exposure of any kind for almost half a mile, imtil the Little Compton
shale outcrops are reached. The line of western outcrop of the granite
must therefore pass somewhere between these regions in a southeasterly
direction. It probably extends west of the road leading north from Little
Compton; 1^ miles south of Little Compton post-office it is known to turn
toward the southwest, reaching Sakonnet River, south of Churchs Cove,
about a mile north of the breakwater. The granites from here south to the
point are often coarsely porphyritic.
SAlSTDSTOlSrE SERIES BETWEEN WINDMILE HIEE AISTD THE COVE
NORTH OF BROWNS POINT.
South of the mouth of the outlet of Nonquit Pond coaly shales are
exposed along the shore, bordering the same for about 700 feet. Then
sandstone occurs on the west of the shales, showing fine cross bedding, made
distinct by thin layers containing more carbonaceous material. The general
strike is parallel to tlie shore, or N. 20° E., dip 45° to 65° W. Farther south
an inward bend of the shore exposes the coaly shale again. These shales
contain indistinct leaf impressions of unknown affinities, and traces of ferns
can still be found. Farther south there is more sandstone, but here east of
276 GEOLOGY OF THE NARRAGANSETT BASIX.
the coaly shale, and dipping 45° E. If this indicates an anticline, it is
evidently a sharp one, and the folding has been obscured in the shales by
abundant cleavage in several directions. It is also a long fold, extending
from the most northern shale exposure for at least half a mile southward.
The sandstone, dipjDing east, at the north has a strike of about N. 5° E.,
following the shore for a considerable distance, and at the south end the
strike changes to N. 30° E., the dip being 50° SE. Beyond this is a fault
having' the same trend of N. 30° E.
In some places the sandstone is very coarse and contains a great
number of small pebbles. Toward the fault the sandstone is often very
quartzitic, somewhat resembling the arkose along the shore, but the quartz
grains are as a rule much smaller in size. South of the fault line the shore
is bordered by sandstone, often coarse, or filled with small pebbles; less
frequently it is decidedly conglomeratic, with much stretched pebbles. Just
south of the fault a fine conglomerate bed was once overlain by black shale,
small patches of which are still scattered over its surface, indicating a
general southerly dip of about 20°. ' Farther south the strike is N. 70° W.,
dip 25° S., but there is also evidence of cross beddi'ng, suggesting shallower
water eastward. Near the most western extension of the shore a long
plant stem is exposed for several feet in the coarse sandstone, but shearing
makes it impossible to identify it. Small plant stems occur near by, resem-
bling the Silver Spring plant stems. Farther south, at the western termina-
tion of the Alray Farm road to the shore, the coarse sandstone, containing
numerous fine pebbles, shows a strike of N. 60° W., dip 20° SW., indicated
by numerous patches of coaly shale, which cover its surface and which
once were connected and formed a continuous layer.
Southward from this region the bedding is often difficult to follow for
anv considerable distance. Not infrequently the stiike is nearly east- west,
and the dip is then southerly, usually about 20°. But at many points along
the shore there is bedding striking more nearly parallel to the shore and
dipping westward, often very steeply. In some cases, especially where the
dip is very steep, this west dip seems to be partly due to folding caused by
pressure transverse to the trend of the border of the basin. Frequently,
however, it is accompanied by distinct evidences of cross bedding. In such
cases a steep westward dip not infrequentl}^ curves westward so as to reach
SANDSTONES NORTH OF BROWNS POINT. 277
an almost horizontal position. At some localities a general study of the
rock indicates that more or less horizontal beds wei'e repeatedly attacked
on the west side by waves. The westward-sloping cut-out margins of these
beds were later covered by similar sand beds, which were themselves nearly
horizontal. This whole series at present dips in a general way southward
at an angle of about 20°. Toward the south the strike seems to be more
nearly N. 60° E., dip 45° E., the dip decreasing rapidly southward until it
becomes only about 10°. Tt is difficult to determine the real strike of the
more southern shore outcrops.
North of the fault line mentioned above, the sandstone rarely contains
pebbles over an inch long. Southward for some distance there are distinct
conglomerate layers. The pebbles usually do net exceed 3 inches in
length, although some beds show pebbles somewhat longer, considerably
stretched. Granite pebbles are not infrequent, but are hardly recognizable
on account of the extreme shearing.
A very coarse conglomerate, some of the pebbles a foot in length,
occurs along the farm road west of the house on the west side of Windmill
Hill. Many of these pebbles are composed of quartzite and are of much
larger size than the pebbles in the exposures along the bank farther south.
They occur between the 60-foot and 80-foot levels.
Nothing is known of the stratigraphic position of these rocks. The
following remarks, however, may be pertinent. The present eastern mar-
gin of the Carboniferous basin, as a rule, shows arkose and coaly shales as
the basal beds. Overlying these is sandstone, often with conglomerate
layers. If the mass of coaly shale, sandstone, and mostly fine conglom-
erate so far described be conceded to re^^resent the basal beds of the
Carboniferous series in this region, then the very coarse conglomerate so
abundantly exposed in the bed of the farm road on the west side of Wind-
mill Hill may be considered as representing a higher horizon and as over-
lying at least the great mass of the sandstones.
If this view be correct, the coarse conglomerate on the west side of
Windmill Hill could then be correlated with the coarse conglomerates
exposed at High Hill Point, Fogland Point, the northwest side of Nonquit
Pond, and thence northward.
278 GEOLOGY OF THE NAREAGANSETT BASIN.
COARSE COjSTGIjOMERATB SERIES ALOKG THE EAST SHORE OF
SAKONNET RIVER.
HIGH HILL POINT.
Southeast of High Hill Point, near the western end of the beach, is an
exposure of very coarse conglomerate, with pebbles often 15 inches long.
An included sandstone layer shows the dip to be about 10° E. At the
south end of High Hill Point the coarse congloiuerate is again exposed.
Near the east there is an included sandstone bed showing horizontal bedding.
Farther west, and higher up the cliff, another interbedded sandstone layer
shows a dip of 10° W. The same dip is shown at the north end of High
Hill, although here the sandstone layer abuts against conglomerate on the
east, and is itself cut off by conglomerate on the west, so abruptly as to
make the real bedding at first sight uncertain. The conglomerate is
exposed in a small indentation north of the hill, and continues along the
bank northward for a short distance. Toward the west of the most northern
exposure of the coarse conglomerate a fine conglomerate overlain by a little
sandstone comes in, having a dip of 30° E., and this is underlain by coarse
sandstone, which in certain layers is so full of very small pebbles, an inch
and less in size, that the rock may be termed a fine conglomerate. Occa-
sionally the rock contains coarser layers, with pebbles up to 1 ^ or 2 inches
in length.
The great mass of the rock, however, is sandstone or the very fine con-
glomerate. It continues to be exposed northward for a quarter of a mile,
the dip, however, soon diminishing to 10° E. The general strike of the
rocks seems to be about N. 10° E. The sandstone is very similar to the
sandstone bordering the shore southwest of Windmill Hill, southward
toward Browns Point, and with this it is correlated. The overl}ang coarse
conglomerate is correlated with the exposure on the west side of Windmill
Hill, just west of the farm house.
FOGLAND POINT.
A short distance north of the southern end of the headland terminat-
ing in Fogland Point, the very coarse conglomerate with large pebbles is
exposed, and from that place northward it borders the shore halfway to
the point. The strike is about N. 10° E., dip 10° E., becoming a little less
WEST OF NONQUIT POND. 279
to the northward. North of the conglomerate, ahnost as far as the point,
the shore hes on a greenish shale, interbedded with a schistose rock which
is evidently a sheared sandstone without pebbles. The strike of this rock
is about N. 10° to 20° E., dip 10° E., and it certainly underlies the con-
glomerate. Its greenish color and shaly character resemble that of the
rock underlying the coarse conglomerate at Eastons Point. At the southern
end of the headland a similar greenish shale is exposed, also striking
N 10° E., and dipping 10° E. This would make this exposure overlie the
coarse conglomerate. If a fault be supposed to intervene, only a slight
displacement would be necessarj^ to bring up the lower shales to this
position. This green shale beneath the conglomerate is believed to be
stratigraphically related to the sandstone and fine conglomerate series below
the conglomerate at High Hill Point.
EXPOSURES WEST OF NONQUIT POND.
A barrier beach connects the headland of Fogland Point with the
mainland. East of the beach lies a broad hill, crossed by an east-
west road. On the western side of the hill the road is crossed by a long
set of very coarse conglomerate exposures, the strike of an interbedded
sandstone being about north-south. This exposure lies not far west of
the line of strike of the exposure on the west side of Windmill Hill, with
which these various conglomerates are correlated.
A quarter of a mile south of Coreys Wharf a bluish-gray to black shale
or fine-grained sandstone is exposed, some of the layers being very black
and shaly. A short distance south of Coreys Wharf the rock is a bluish
sandstone. No trustworthy strikes and dips could be followed for any dis-
tance; but these exposixres are believed to underlie the coarse conglomerate.
Lithologically they are somewhat similar to the more northern rocks
exposed along the shore west of Windmill Hill.
The very coarse conglomerate is exposed at various points alono- the
80-foot hill west of the north end of Nonquit Pond. North of the east-
west road one interbedded layer of sandstone shows a westward dip of
10°. The strike is probably about N. 10° E.
280 GEOLOGY OF THE NAR HAG AN SETT BASIN.
EXPOSURES BETWEEN TIVERTON FOUR CORNERS AND THE NORTHEAST SIDE
OF NANNAQUACKET POND.
Northwest of Tiverton Four Corners a tract of meadow land and marsh
runs toward the bay North of this, a Httle east of north from the last
exposure described, the coarse conglomerate is exposed in several places.
The more northern exposure shows a strike of N. 32° E., dip 50° W.
Eastward, on the western side of the hill, west of the road, are several
exposures of coarse conglomerate not showing a marked strike or dip.
The line of strike of the exposure described above, if extended, would reach
a hill showing steep cliffs on the western face, where interbedded sandstones
show successively, northward: strike N. 50° W., dip 60° W.; strike N. 75°
W., dip nearly vertical, and strike N. 30° W., dip 70° W. Northward a
small exposure shows a strike N. 5° E., dip about 70° W. A large steep expo-
sure northward has the same northerly strike. The next has a strike N. 45°
W., dip 60° W. Northeastward, nearer the road, are several exposures, the
most western of which has a strike north-south, dip steep west. Then,
after a rather long interval, in the southeast angle of the crossing of the
Tiverton with the Sapowet Point road, the coarse conglomerate is exposed
again with a strike of N. 70° W., dip 35° SW. The most westerly exposure
north of the Sapowet Point road shows a strike also N. 65° W., dip 60° W.
Nearer the crossroads the dip seems very low southwest. At an inter-
mediate point northward the strike is N. 15° W., dip 30° W. No satis-
factory bedding is shown by the exposures in the little creek which runs
west about a quarter of a mile from the crossroads. In the valley of this
brook, however, a little east of the line of outcrop of the conglomerate, occurs
a sandstone and shale exposure, in places of a rather dark color, which
may represent the sandstone series underlying the coarse conglomerate.
Unfortunately, the exposure is not large enough to determine the matter.
North of this little stream, on the western side of the summit of the
hill, a series of exposures continues northward. One of these shows a
strike N. 40° E., dip steep, perhaps 60° W. (uncertain). The most northern
exposure, on the north side of a circular embankment, shows strike N. 80°
E., dip 85° N. Northeast of the private road, on the slope toward Naniia-
quacket Pond, an exposure has a strike N. 85° E., dip 75° N. After that
the exposures continue to trend northward east of Nannaquacket Pond.
Coarse conglomerate is exposed along the Tiverton road not far north of
LITTLE COMPTON SHALES. 281
the southern end of the pond; strike N. 85° W., dip 60° S. Northwest,
near the end of a point projecting into Nannaquacket Pond, is dark, ahnost
black, sandstone, which seems to strike N. 75° W., dip almost vertical.
It may be sandstone belonging beneath the coarse conglomerate series. In
that case a fault or sharp anticlinal fold must be imagined along its north-
east side. At the bend of the road, nearly east, the conglomerate strikes
N. 75° W., dip 70° S. Near the north end of the hill forming this exposure
unsatisfactory exposures indicate a strike of N. 35° W., dip 70° E. North
of a small stream a small hill occurs west of the road. Near its southern
end coarse conglomerate is exposed. Northwest, at the shore, an inter-
bedded sandstone layer shows strike N. 3° E., dip apparently 50° W.
South of the creek and east of the road numerous bowlders of dark-blue
to black sandstone, sometimes shaly, occur toward the northern end of a
hill. The trend of the hill is N. 10° E. These sandstones are of the kind
which underlie the coarse conglomerate series and which are found eastward
in the series resting upon the granite associated with and over the arkoses.
The greatly varying strike and dip of the coarse conglomerate series
here described may be partly due to cross bedding. In still larger meas-
ure, however, it is the result of the breaking up of the conglomerate series
by a system of faults into numerous large masses or blocks, with frequent
and variable tilting, but not enough to disguise the essential unity of the
series. In general these blocks show a northward strike and westward dip.
At Fogland and High Hill Points, however, there are low eastward dips
showing a shallow syncline between this and Windmill Hill. Southward
this syncline probably became strongly accentuated, giving rise to the steep
eastward dips of the coarse conglomerates on the west side of Sakonnet
River from Black Point to Smiths Beach.
On the west side of the neck west of Nannaquacket Pond, about two-
thirds of its length from its north end, occur several exposures of grayish
sandstone and of conglomerate with medium-sized pebbles, of which the
stratigraphic position can not be determined.
LITTLE COMPTOK SHALES.
From Browns Point to the south side of Pachet Brook southward,
within half a mile of the road running north from Little Compton, thence
westward and along the shore as far as the granite area, extends a series of
slates and shales which evidently constitute a geological unit. The most
282 GEOLOGY OF THE NAEEAGANSETT BASIN.
northern exposure of these shales along the shore is at Browns Point, along
the northerly trend of the shore line. A second similar exposure occurs
where the shore turns toward the southeast. The strike of the more
northern exposure is N. 32° E., dip 45° E. The more southerly exposure
has a strike N. 20° E., dip 4.5° E. The rock is of a greenish color, and
has been cleaved like the rocks east of the brook.
The next exposure of the series occurs almost east of the mouth of the
brook, a little south, near the 20-foot level on the hillside. A quarter of a
mile northward exposures occur along a road leading eastward up the hill.
From this point there is a succession of exposm-es extending northeastward
up the hillside. This line of outcrops crosses the road at one of its more
marked bends on the summit, continuing in the northeasterly direction
alono- the hilltop and down the northeastern slope to a point a short distance
north of the first road leading east.
The series evidently underlies the whole of the hill east of Browns
Point. The ordinary appearance of the rock is that of a very fine-grained
whitish quartzite traversed by cleavage planes, usually a fifth of an inch
apart, along which black mica is abundantly developed. The result is a
general stratified appearance of the rock, the strike of the cleavage being
on the average N. 40° E., dip very steep, almost vertical. Behind the barn,
east of the angle of the road mentioned above, the rock is fine grained,
greenish, slightly banded with darker material. Southeast of this hill occurs
another elevation, not marked upon the United States Geological Survey
map, occupying the middle area of the quadrangle formed b}- the roads
northwest of Little Compton. The whole of this hill is also underlain by
the cleaved fine-grained whitish quartzitic rock. The exposures are most
frequent on the western and southern slopes. The more northern outcrops
on the western sides show a cleavage running about east- west; farther south
and southeast it runs about N. 25° E. The rocks are here evidently much
contorted and wrinkled. The stratification in places is clearly not in
ao-reement with the cleavage. It is very desirable carefully to work out
the real plane of bedding of this quartzitic rock and to determine its dip
and strike. The shore exposures farther southwest, however, suggest that
the general dip is southeasterly.
South of Browns Point is a cove. At the headland forming its south-
ern extremity the rock is shaly. Exposures occur southward along the
BEOWNS POmT TO CHUECHS COVE. 283
shore at low tide. A third of a mile south of the cove, along the shore, the
fissile green shale shows purplish coloring along certain beds, and in places
there seem to be fine bands of a dolomitic limestone showing a pinkish
coloring. The strike here is N. 8° E., dip 15° E. A quarter of a mile
southward the sti-ike is N. 20° E., dip 35° E. At Churchs Point the shales
strike N. 15° E., dip 40° E. A third of a mile southeast, south of the
mouth of a small stream, there is an exposure too massive to indicate the
attitude of the beds. Farther south close observation shows a fine-grained
rock cleaved very much like that of the two hills toward the north, first
described; strike N. 30° E., dip 40° E. Massive rock occurs again a
quarter of a mile south of the stream last mentioned, in a small indentation
of the shore line; also at the projecting outline farther south, and at the
next two similar projections of the shore. The strike is apparently N. 10°
E., dip 60° to 70° E. North of the angle in Churchs Cove the rock has
again a more whitish quartzitic appearance; strike N. 10° E., dip 25° E.
A short distance south of the point where the shore line takes a southerly
trend the greenish shale is again exposed. Certain layers are tinged with
purple, and pinkish or light-red very thin dolomitic bands are again seen;
strike N. 15° E., dip 15° E. The greenish shales continue to be exposed
all along the shore as far as the granite area. Just north of the granite area
they are again frequently tinged with purple and also show the very thin
dolomitic bands. Their strike is N. 3° E., dip 20° E. The tingeing of
purple with the thin banding of dolomitic material suggests that these shales
are identical with the shales forming the western third of Newport Neck.
A distance of about 50 feet intervenes between the above-described
shales and the next exposure of rock. This is a rather dark rock, con-
taining abundant brecciated fragments of a dark-greenish stone, and appar-
ently also fragments derived from a granitic mass. It strikes in a direction
about N. 40° E., and evidently follows the northern line of the granite mass.
It is believed to be a breccia formed during the faulting which brought the
shales and the granite into juxtaposition here.
The green Little Compton shales are believed to be of pre-Carbonifer-
.ous age. The granites on the south are also considered pre-Carboniferous.
The granites may, however, be more recent than the Little Compton shales.
In that case the shales near the contact would appear more massive and
more like hornstone, resembling the Dumpling rock south of Jamestown on
Conanicut.
CHAPTER VI.
AQUIDNECK, OR THE ISLAND OF RHODE ISLAND, WITH THE
ISLANDS OF NEWPORT HARBOR.
ARKOSE AND PRE-CARBOIiriFEROUS ROCKS ON 8ACHUEST NECK.
At the promontory almost half a mile south of Flint Point, greenish
shaly rocks are exposed along the immediate shore, but farther out the
promontory is composed of arkose. Interbedded layers of coaly shale show
that the arkose occurs in the form of a low anticline, whose axis pitches
northward at a low angle and trends parallel to the general coast line, about
N. 20° E. It is evidently a great block of grit which once lay above the
level of the green shale series, but was dropped by faulting down to its
present position in the green shale area.
Along the shore the green shales occur as far northward as a point a
quarter of a mile south of Flint Point. Here they change from their former
trend of N. 20° E., dip 60° W., to N. 45° E., dip 35° W. A short distance
north the arkose series comes in with a similar strike and a nearly vertical
or steep western dip. The strike changes rapidly to N.-S., dip 45° to
60° W., and continues as far as the quartz-veined promontory southeast
of Flint Point. Between this and Flint Point interbedded coaly shales
show that the arkose series dips about 70° W. West of the point the dip
becomes almost vertical, then 70° to 60° E., then 75° E., 60° E., 35° E.,
and 80° E., the exposures of the arkose series terminating on the shore
about 600 feet southwest of the point. A closer examination of the line
of exposure between this more western point and Flint Point shows that
the arkose is here several times closely folded, the western sides of the
folds being sometimes a little overturned, in consequence of which there
appears to be a fairly general steep eastward dip. Coaly shale layers
are frequently interbedded with the arkoses, the latter, however, predomi-
nating. These coaly shale layers are very numerous elsewhere in the series,
284
ARKOSE ON SAGHUEST NECK. 285
and are frequently present on the west and southeast sides of Sachuest
Neck. On these sides at least 300 feet of arkose matei'ial is exposed.
On the western side of Sachuest Neck the exposures begin not far from,
the beach. A coaly shale bed belonging in the arkose series lines the shore
at its upper margin, against the hillside, for a long distance. Fern-leaf
impressions and species of Annularia occur in this layer just northwest
of some old farm buildings. The dip is about vertical or at times very-
steep eastward at the north end, but southward it is more regularly and
decidedly west. Westward, near low-tide levels, the arkoses show a lower
western dip, and this low westward dip becomes more marked and more
general southward. At very low tide the arkose series is seen to change
from its ordinary strike of N. 15° E. to N.-S., and then to N. 20° W. north-
ward at one point near the northern end of these western exposures. These
features probably indicate a secondary synclinal structure west of the neck.
The westward dips continue as far as the point. Near the point the strike
is about N. 23° E., dip 45° W. Along the east side of the point there is a
well-marked fold whose axis trends N. 8° E. This can be followed north-
eastward along the shore, and 250 feet north from its most southern expo-
sure the axis of the fold turns quite abruptly eastward, so as to trend
N. 50° E. Then it changes again to a more northerly direction, showing
synclinal structure on the northwest side, and on a larger scale on the
southeast, the trend northward seeming to be N. 16° E. Not far from the
most northeastern exposures of the arkose series a small fold is shown, its
axis trending N. 8° E., its anticlinal nature being not &,t first sight very
noticeable, owing to a slight overturn of the fold in part of the exposure.
The most eastern arkose exposures show a strike about north-south ; the dip
is about 20° to 30° W. Along this most eastern exposure the arkose at
low water shows on the east of the normal arkose a very granitic-looking
rock in which the feldspar can be easily recognized. Farther up the beach,
near high-water mark, the arkose shows at its base a mass of unquestioned
coarse porphyritic granite, about 3 feet long, with phenocrysts of feldspar,
like those at the Cormorant Rock, over a mile southward, and elsewhere.
It can not be determined whether this is only an included bowlder or the
upper part of the granitic mass which once furnished the material for the
arkose. From the well-preserved feldspars in the granitic rock toward
the sea, it is evident that if this lower rock be not itself g-ranite the original
286 GEOLOGY OF THE NAERAGANSETT BASIN.
granite mass could not have been far away. It seems probably that the
porph3a'itic granite near high-tide level niay be a part of the original
granite mass and not a bowlder derived from the same. The existence of
this granite with large feldspar phenociysts at Little Compton, and south-
east of Almys Pond, south of Newport, as well as at the Cormorant Rock,
makes such a supposition not impossible.
PRE-CARBONIFEROUS ROCKS.
The Island Rocks and other associated rocks off the northeast coast of
Sachuest Neck are all composed of a greenish rock, varying between a
slate and a shale, striking about N. 24° E. and dipping westward. The
Island Rocks resemble very much the more quartzitic rock in the hill
exposures east of Browns Point. The green shales are also exposed along
the east shore of Sachuest Neck, from a point a quai'ter of a mile south ot
Flint Point to the arkose promontory a quarter of a mile farther south.
Near its northern end the shale contains a little conglomerate, striking N.
43° E., dip 35° W. This changes soon to strike N. 33° E., dip 60° W.,
this strike and dip being' maintained as far as the arkose promontory. At
the north end of the cove, southwest of the promontory, the rocks strike
N. 35° E., dip 35° W. ; southward in the cove the strike changes to N. 40°
E., then N. 45° E. toward the southern side of the cove, changing to N.
30° E., dip 60° W., near the south end of the cove. The more southern
exposures along the cove show considerable conglomerate with angular
fragments, and from this point southward most of the rock is conglomeratic-
A whitish sandy band makes its appearance in the cong-lomeratic greenish
rock. It is similar to some of the more quartzitic rock in the Little Comp-
ton shale series on the hill east of Browns Point. This can be followed for
a considerable distance, having strike N. 30° E., dip 60° W. at the north
end, becoming steeper southward. The shore here makes a convex curve.
Toward the southern end of this the strike is still N. 33° E,, dip 80° W.,
but immediatelv beyond the strike becomes N. 58° E., dip 70° E., chang-
ing soiithward to N. 53° E., dip 60° E., and then, at another convex curve
in the shore line, to N. 35° E., dip 45° E. Southward there is a small
promontory halfway between the arkose promontory and Sachuest Point
The strike here is N. 63° E., dip 60° E. West of the cove formed by this
promontory the strike is N. 22° E., dip 80° E., becoming N. 30° E., dip
PEE CARBONIFEROUS ROCKS OF SACHUEST NECK. 287
80° E., at the line of faulting- separating this rock from the arkose series.^
A short distance east of this fault line the rock contains a diabase dike.
It will be noticed that about halfway between the southern termina-
tion of the greenish conglomeratic rock and the arkose promontory the dip
changes from steep east to steep west. North of the point the exposures
seem to be successively lower. Southward toward the fault line appai--
ently higher horizons are reached. Close observation, however, shows no
signs of a fold there, where the steep dips change du-ection. A strong
flexure in the rock previous to the faulting which exists farther westward
seems to be the explanation, the flexure being of such a character that at a
certain point the conglomeratic strata are nearly vertical. North of this
point they dip westward; south of this point, eastward.
Exposures of the greenish congdomerate also occur on the hillside
toward the southern part of the hne of shore exposures. A line connect-
ing the extreme shore exposures west and south would trend N. 22° E.,
and would pass just west of the most western of the hill exposures.
The position of the conglomerate with reference to the greenish shales
is luicertain, but after detailed work on this question it was supposed to
overlie the same, owing to the westward dip of the series northward
toward the Island Rocks.
While the shales have the ordinary clastic appearance the conglomeratic
beds present certain peculiar features. In the first place, the pebbles are
usually decidedly angular in appearance, presenting, commonly, the aspect
of fragments in a breccia. In the second place, there seems to be no marked
tendency to arrange the fragments in layers according to size, as is commonly
the case when fragments are transported by water action. In the third place,
a lai'ge part of the fragmental material is lighter or darker in color than the
cementing material when seen on the weathered surface of the rock. When
broken, however, this distinctness to a great extent disappears, and the whole
mass looks greenish, varying chiefly in fineness of grain. This is a feature
more commonly observed in breccias than in genuine conglomerates. In
the fourth place, the variety of material occurring in the form of fragments
varies sufficiently to include four or five types. Some of these fragments
seem to be certainly from some clastic rock. Others ms,j be of igneous
' Prof. T. Nelson Dale raises the very pertinent question wliether the facts may not be explained
by assuming an unconformity, since Carboniferous arkose would probably rest in an unconformable
manner upon Cambrian shale.
288 GEOLOG^Y OF THE NAERAGANSETT BASIN.
origin, but they do not resemble any known rock in the Carboniferous basin.
Fragments of a reddish rock, often resembhng jasper, occur here and there.
In the fifth place, the absence of granite in the form of pebbles is very
noticeable.
In several of these particulars the greenish Sachuest conglomeratic rock
resembles the more northern exposures of the Dumpling rock on the eastern
shore of Conanicut, south of Jamestown. There seems to be no question
of the pre-Carboniferous character of the greeriish rock, both shale and
conglomerate. The absence of all granite fragments from the green series
suggests that the granite is intrusive and therefore of later origin. The
nearest granite exposures of any size are now at Cormorant Rock, but the
ex^Dosure just beneath the arkose series suggests that it once reached as far as
Sachuest Neck. The arkose series probably once rested upon the green
series, a relation now obscured by faulting. It derived its materials, at least
the coarser part, from the granite, which is therefore pre-Carboniferous. The
grit is Carboniferous, as is shown by the interbedded coaly shale layers
containing fossils. The interbedding of coaly fossiliferous shales with the
grit seems to be characteristic of exposures along the eastern margin of the
Narragansett Basin, several such occurrences being known at Steep Brook,
Fall River, and Tiverton. The relative age of this eastern arkose as com-
pared with that of the Aquidneck shale series can not be determined at
present.
EASTERN SHORE OF AQUIDTSTECK ISLAND AS FAR SOUTH AS THE
SECOND COV3 NORTHWEST OF BLACK POINT.
The most northern exposure of Carboniferous rock on Aquidneck
Island on the east shore occurs southwest of the cove, near the eastern
base of Butts Hill. Coaly shale and sandstone are interbedded, being
several times repeated southward for half a mile, as far as the wharf east
of Portsmouth village. North of the wharf a short distance there is evidence
of a low anticline, pitching southward, the dip being low on both sides.
The exposures at the wharf and southward belong to the western side of
this anticline, and therefore all dip westward. At the wharf there is sand-
stone on the north side, showing a cleavage dipping 60° W. Overlying
the sandstone on the south side is a thin \fijer of conglomerate dipping
about 10° E. But south along the shore exposures of conglomerate
and dark coaly shales strike N. 3° E., dip 45° W. Southward sandstone
EASTERN SHORE OF AQUIDNECK ISi^AJSTD. 289
borders the shore, interbedded with a few coaly shale layers and a few
thin conglomerate beds with small pebbles and flakes of carbonaceous
shale; strike N.-S., dip 20° W. Yet farther south gray sandstone is
abundant. Interbedded with this, south of a small stream, a third of a
mile from the wharf, is black coaly shale; strike N.-S., dip 30° W.
Half a mile south of the wharf the coaly shale contains impressions
of fern leaves; strike N. 3° E., dip 40° W. Southward occurs sandstone,
overlain by several feet of fine conglomerate, the pebbles not exceeding
1 inch in length; dip 30° W. PYom the wharf southward rocks con-
tinually higher in the series are exposed, but owing to the fact that the
strike is almost parallel to the shore, only a small thickness of strata is
traversed.
From this fine conglomerate exposure southward the strike seems to
be a little east of south, while the shore line curves inward in such a way
as to expose, a, third of a mile southward, gray sandstone in the form of
large loose blocks. Then, two-fifths of a mile southward, large blocks of
coaly shale occur, representing the highest rocks so far described. A third
of a mile southward the gray sandstone seems to be repeated, descending
in the series; strike N. 7° W., dip 10° W. ; and only a short distance
beyond, southward, the almost horizontal sandstone contains thin con-
glomerate layers with pebbles up to 1 inch in length. The more southerly
of these exposures dip 10° W. The thin conglomerate layers continue to
occur in the sandstone southward, and at several places they contain the
fragments or flakes of coaly shales noted above.
In the Glen almost half a mile of exposure is seen. The rock is
evidently the shale series, very much blacker and more coaly than the
corresponding rocks on the west side of the island. East, toward the bay,
about 25 feet above the water level, a Cordaites leaf was found in the
shale. About 40 feet above the water level there is sandstone interbedded.
A comparison of the Glen section with the shore exposures from McCurrys
Point southward beyond Sandy Point shows that the shore exposures also
belong to the shale series. As far as can be determined the shale series at
the Glen di^DS low, 5° or 10° E. It certainly is nearly horizontal
Between the Glen and the beach of Sandy Point there is exposed
sandstone sheared into a shaly rock, the shearing planes dipping east of
south. No bedding could be recognized. South of the beach of Sandy
MON XXXIII 19
290 GEOLOGY OF THE NARRAGANSETT BASIN.
Point coaly shale comes in again. A quarter of a mile soiithward this has
evidently been violently squeezed in an east-west direction.
South of McCurrys Point a small stream entering the bay from the
west exposes from the shore to a considerable distance up the hill westward
nothing but bluish-black shale of the type found so abundant on the west-
ern side of the island over the coal regions. These bluish-black shales
evidently overlie the coaly shales, sandstones, and fine conglomerates so
far described, and a small fault has probably thrown them a little eastward
near the point. The cleavage obscures the stratification. The cleavage
dips 15° to 20° W., and there seems to be a southward dip of perhaps no
more than 5°. Southward the shale becomes blacker and more coaly and
seems to be nearly horizontal. A quarter of a mile north of the mouth of
the creek traversing the Glen it contains impressions of fern leaves. The
coaly shale continues as far as the Glen.
A mile south of Sandy Point, or a little over half a mile from the
southern extremity of the beach, dark-gray sandstone makes its appearance
again. Over it occurs, southward, coaly shale, apparently dipping eastward,
but this dip is of little moment, since southward there is abundant evidence
of violent crumpling and folding of the rock by a force acting in an east-
west direction. Southward more sandstone is seen sheared into a shale.
The absence of clear indications of the bedding at this locality and as
far northward as McCurrys Point, and the violent crumpling at the last-
described locality as well as south of Sandy Point, afi"ord serious difficulties
in attempting to determine the stratigraphic position of the coarse conglom-
erates in the southeastern part of Aquidneck.
The great Aquidneck shale series exposed at the Glen and along the
shore is believed, however, to be overlain north of Black Point by the
coaly Sakonnet sandstone with fine conglomerate, representing a section of
much smaller thickness, 110 feet being exposed at the point, and this in
turn is overlain by the coarse Purgatory conglomerate, whose maximum
thickness as exposed along the shore apparently does not exceed 380 feet.
COARSE CONGLOMERATES AND UNDERLYING SANDSTONE SERIES
FROM BLACK POINT TO THE NORTH END OF SMITHS BEACH.
About a quarter of a mile northwest of Black Point is a second promon-
tory. In a cove immediately toward the west of the latter is bhiish sand-
BLACK POINT TO TAGGARTS FERRY. 291
stone. A thin conglomerate layer with small pebbles shows a strike of
N. 53° E., dip at first lower, then 30° SE. Eastward along the strike
the sandstone becomes decidedly darker and more carbonaceous, the strike
changing to N. 35° E. On the east side of the promontory the strike is
N. 32° E., dip 45° SE. The dark carbonaceous sandstone series is con-
tinued on the east side of the promontory along the northern side of the
cove north of Black Point. About 110 feet of the sandstone series are
exposed. The lower 90 feet consist of the carbonaceous sandstones already
described, with which are intercalated thin conglomerate beds with pebbles
not exceeding 1 inch in size. Then occurs a layer of coaly shale 1 foot
thick, above which are 7 feet more of the dark sandstone. Above are 8 feet
of conglomerate with small pebbles, and, finally, 4 feet of the dark sand-
stone. On the north side of the cove north of Black Point the strike is
N. 68° E., dip about 45° SE. Southward there is no exposure until the
middle of the cove is reached, when the very coarse conglomerate comes
to view.
The general strike of this conglomerate is about N. 22° E. At the
northern end of the shore exposures, however, there is marked variation in
strike. Near the middle of the cove the conglomerate includes a sandstone
layer apparently striking N. 3° E., dip 80° E. Nearer the south end of the
cove the strike is N. 48° E., dip about 60° E. South of Black Point the
strike is N. 28° E., dip 60° E., the strike becoming about N. 22° E. farther
south.
Notwithstanding this irregularity in the strike of the sandstone and
conglomerate series, and especially the discordance between the average
strike of the two series, the sandstone is believed to underlie the coarse
conglomerate, the dips certainly favoring this view.
That part of the exposure from Black Point two-thirds of a mile
southward is serviceable in estimating the thickness of the conglomerate
series. About 380 feet of the coarse conglomerate series are exposed. The
lowest part of the section is found near the northern end of the line of
exposures. The upper beds are exposed along the shore, farther south.
Beginning with the lowest part of the section, four beds of conglomerate
maybe distinguished, 19, 20, 11, and 32 feet thick. Above these He 35
feet of sandstone, separated by a thin conglomerate layer from 29 feet more
of sandstone; next, a thin black shale layer, then 23 feet of conglomerate,
292 GEOLOGY OF THE NAREAGANSETT BASIN.
at the top including fragments of coaly shale, followed by a 4-foot layer of
conglomerate, also including fragments of coaly shale at the top. Above
the conglomerate are 2 feet of coaly shale, 12 feet of conglomerate, 6 feet
of coaly sandstone, 15 feet of grayish-black sandstone, 5 feet of grayish
sandstone, 2 feet of black coaly shale, 14 feet of dark-gray sandstone, two
layers of conglomerate 15 and 7 feet thick, 13 feet of sandstone, and, at the
top of the section, three layers of conglomerate, 33, 23, and 27 feet thick.
A generalized statement of the chief characteristics of this section would
be 82 feet of coarse conglomerate at the base, followed by 99 feet of sand-
stone, 41 feet of coarse conglomerate, 42 feet of sandstone, and 118 feet of
conglomerate. The thickness of the great interbedded sandstone layers
should be especially emphasized when the attempt is made to determine
the relative horizon of isolated small sandstone and coarse conglomerate
outcrops.
Along the line of outcrop described above, the dip varies, southward,
from 60° E. to 45° and 40° E., becoming again 60° E. toward the southern
end of the section described. Southward along the shore, at a promontory
a mile south of Black Point, the dip increases to 80° E. The steep east-
ward dip continues southward, becoming 80° W. at Taggarts Ferry Cove,
bnt returning to 75° E. again on the south side of the cove.
The very coarse conglomerate borders the eastern shore of Aquidneck
Island as far southward as the north end of Smiths Beach, except in tlie
cove two-fifths of a mile north of Woods Castle, known as Taggarts Fen-}-,
where rocks occur varying between coaly sandstone and coaly shale.
On the shore west of the southern end of the cove, and along the
creek south of these exposures, dark carbonaceous shale and sandstone are
exposed for 30 or 40 feet. The shale series is believed to merge gradually
upward into this peculiar coaly, carbonaceous shale and sandstone. East-
ward along the shore overlying these land exposures is more sandy rock of
the same character. Overlying this is found a coarser sandstone, overlain
in turn by carbonaceous shaly rock, the dip varying from vertical to 85°
W. Then comes, eastward, a coarser sandstone, with small pebbles, dipping
80° W. Toward the north, along the shore, a sudden twist causes the con-
tact between this rock and the overlying carbonaceous shale to dip due
east. Farther east, coarser sandstone, with fine conglomerate overlying it,
TAGGARTS FEERY TO SMITHS COVE. 293
dips more steeply, 55° E Overlying this, conglomerate with medium-
sized pebbles dips 70° to 80° E. Then comes a comparatively thin layer
of coaly sandstone and a conglomerate with pebbles of medium size, both
dipping 80° E. Then a considerable thickness of dark-gray, more car-
bonaceous shaly rock is exposed, and an equall}^ thick bed, perhaps 40
feet, of rather coarse conglomerate, dipping 80° E. Overlying this occurs
carbonaceous sandstone, with coarse conglomerate farther east; dip vertical
or 80° E. along the promontory which they form at the north end of the
cove; but farther north, along the shore, the same beds dip 80° W. This
same dip, varying to vertical, is shown for some distance northward, until
the beds gradually incline more and more eastward, as already noted.
South of the cove the dip is 75° E. It is evident that the same beds of
coarse conglomerate, with the underlying sandstone series, have been
folded in such a way as to dip more steeply in coming southward along the
strike toward Taggarts Ferry; at the ferry there is a slight overturn, the
dip being 80° to 70° W., and immediately south of the ferry the dip returns
to 75° E. with sufficient suddenness to denote a stronger flexure at the
southern end of the cove
The Sakonnet sandstones in the cove and westward correspond strati-
graphically to the sandstone north of Black Point.
From the cove southward to Woods Castle we pass from lower to
higher rocks in the conglomerate series. The dip is steeply eastward —
usually about 70° E. At Woods Castle a bed of coaly shale occurs, over-
lying that part of the conglomerate series forming the shore. It contains
abundant fern remains. Eastward, after an interval of perhaps 30 feet,
probably also underlain by shaly rock, the great isolated mass forming the
conspicuous feature of this coast line is exposed. It is composed, at least
on the west side, chiefly of coarse sandstone. The stratigraphy was not
carefully followed, but the coaly shale bed seems to correspond to a more
sandy, coaly shale exposed about a quarter of a mile north of the cove at
Taggarts Ferry, and the sandstone overlying it replaces a coarse conglom-
erate. In other words, the fern locality at Woods Castle occurs well within
the coarse conglomerate series, and not overlying the same. Southward,
toward Smiths Cove, the dip is less steep, becoming, near the southern end,
as low as 50° or even 45° E.
294 GEOLOGY OF THE NAKKAGANSETT BASIN.
COARSE COIVGLOMERATES AND UNDERLYING ROCKS ON THE NECK
AT EASTONS POINT.
Ou the eastern side of the neck, at the west end of Sachuest Beach,
the very coarse conglomerate series is well exposed along the shore for a
length of almost half a mile, terminating southward in a long narrow
promontory projecting into the sea. The strike of this conglomerate is
about N. 20° E., dip 60° E., southward becoming only 45° E. "West-
ward, beneath the conglomerate is greenish sandstone, often shaly. Inter-
bedded with this is conglomerate, but not equaling the sandstone in
quantity, and the pebbles are also much smaller than those in the very
coarse conglomerate. The dip is still 45° E. Southwestward along the
shore, still lower rocks are exposed — greenish shaly sandstone and shale,
with conglomerate of rather small pebbles. The dip is 45° E., and the
strike is still N. 20° E. Thence to Eastons Point there is a series of
underlying greenish shaly sandstone and fissile shales, having an eastward
dip. So far the exposures beneath the coarse conglomerate are so little
divergent from the strike of the shore line that the section as far as the
point does not represent any great thickness. Going northwestward from
the point, we meet still lower rocks. At first greenish shaly rock continues
the descending section, containing a little conglomerate a short distance
west of the point. At one point west of the southern end of the neck ripple
marks are seen in the shales. Nine hundred feet northwest from the point
intercalated sandstones indicate a local increase of dip to 70° E., and then
toward the axis the dip is lower eastward. The axis of the anticlinal fold
is about a third of a mile northwest of Eastons Point. The dip on both
sides is low. The pitch of the fold is about 10° S.
West of the anticline the dip is at first low W, 20°. This continues
for some time until, about half a mile from the point, the dip increases to
45° W., the strike being still N. 13° E. Here are intei'calated gray sandstone
and conglomerate composed of small pebbles corresponding to the con-
glomerate just west of Eastons Point. Farther northwest the conglomerate
layers become I'ather frequent, the dip being 45° W.; and this continues for
some distance along the shore. The pebbles are only of medium size.
Locally the dip becomes steeper west, at one point 80° W., but it soon returns
to very low west, and then 45° W. again; near this point the very coarse
conglomerate makes its appearance once more, about three-fifths of a mile
PARADISE ROCKS. 295
from Eastons Point, and a fifth of a mile southeast of the first exposures
east of Eastons Beach. Northwestwai-d the coarse conglomerate continues,
with interbedded sandstone and a little carbonaceous shale. The dip
decreases from 45° W. to 15° W. Westward along the shore the very
coarse conglomerate with interbedded sandstone continues, the most
western exposui-es becoming nearly horizontal, dipping at a low angle east-
ward, from 5° to 10° perhaps. At the extreme western end of the exposures
the conglomerate shows an interbedded layer of dark carbonaceous sand-
stone, so disjointed by small faults along joints as to obscure at first sight
the evidences of its former continuity. This layer, when reconstructed,
indicates an eastward dip of 10° to 15°.
Comparing the two sides of the anticlinal fold,- the western side is seen
to have a lower dip. This feature is especially well shown near the extreme
ends of the shore exposures, the dip at the Purgatory rocks being at least
60° E., while on the west side the dips for a long distance along the shore
are low west, and then east, being in places practically horizontal. The
shales on the western side of the fold are perhaps a little more carbonaceous,
but in general the rocks show only a dark-gray color. In comparison with
this the shale and sandstone series at Taggarts Ferry are very much darker,
often black, and show a similar intercalation of medium-sized conglomer-
erates just below the coarse conglomerate series. Near Black Point the
series contains chiefly sandstone, which, although carbonaceous, is not so
dark as the Taggarts Ferry exposure. Moreover, the change from fine
conglomerate to very coarse conglomerate seems to be here more sudden.
PARADISE COARSE CONGLOMERATES.
PARADISE ROCKS.
The continuous exposures of the coarse conglomerates forming the
eastern side of Eastons Point terminate northward at Sachuest Beach.
The same series farther northward forms the Paradise Rocks. The lower
beds of the conglomerate series are exposed a third of a mile north of the
beach, west of the road, near a stream. They are chiefly sandstone, with
a few conglomerate layers; strike N. 12° E., dip 70° E. Farther east,
just west of the road, there are, almost in situ, very large conglomerate
bowlders, with large pebbles, forming the base of the coarse conglomerates.
296 GEOLOGY OF THE NARRAGANSETT BASIN,
The sandstone beneath the conglomerates is again exposed five-sixths of a
mile north of the beach, an eighth of a mile east of the road, north of
a farmhouse. Here it is a bluish sandstone and dips about 40° E. The
basal conglomerate not far eastward dips 60° E.
Almost the entire thickness of the coarse conglomerates exposed at the
western Paradise Rocks belongs unquestionably to a single eastward-dipping
series, combining northward to form the higli ridge Avhich is the conspicu-
ous element of the landscape. At the more southern exposures west of the
reservoir the conglomerate beds form a series of parallel ridges in the fields;
strike N. 18° E,, dip east. Noi'thward, the second field containing exposures
shows a dip of 60° E. in one of the middle ridges; this dip is better
shown southeast of a house. The most eastern ridge, forming a steep cliff"
bordering the reservoir, has coarse conglomerate dipping 40° to 46° E.
Passing northward out of the grounds immediately surrounding the Bel-
mont House, the naore western conglomerates form the southern end of the
high conglomerate ridge, to which reference has already been made, dipping
50° E. on the west side and 60° E. on the east side, while the contin-
uation of the conglomerate bed, bordering the reservoir, still dips 45°
E. Farther north the bluish sandstone beneath the conglomerate series,
already described, dips 40° E. The most western conglomerate exposures
dip 60° E. Farther uj) the conglomerate ridge the dip becomes 80° E.,
diminishing on the east side to about 40° E. on the northward continua-
tion of the conglomerate which farther southward borders the reservoir.
Northward, at the quarry on the west side of the main ridge, the dip has
diminished to 45° or 50° E., and as the strike swings eastward so as to
become N. 30° E., the dip on the eastern side diminishes for a long distance
to 30° E.
These exposures, with easily recognized eastward dip, terminate at
an east-west field wall about a third of a mile south of the east-west
road bordering the Paradise tract on the north side. East of the last
exposure with marked eastward dip, and east of its line of strike, the
exjjosure north of the fence shows an almost vertical dip, or 80° W.
Eastward, in the field, a dip of 50° E. was noticed. A short distance to
the southeast of these exposures, and east of their line of strike, the second
and more eastern ridge of the Paradise Rocks begins. At its north end the
dip is 70° to 80° E. This continues southward, as well as can be deter-
PARADISE ROOKS. 297
mined, notwithstanding evidence of some degree of folding. A subsidiary
ridge west of the main line of outcrop shows almost vertical dips — 80° E.
on the east side, 80° W. on the west side — owing to a moderate diver-
gence of the bedding planes of the two extreme layers. Southeastward
the main line of outcrop begins again, with a dip of 85° W., and this
nearly vertical dip is maintained for some distance south, becoming 70°
W. at the most southern exposure, between the middle and western streams
entering the reservoir.
A very important point should here be noted. While the mass of con-
glomerates forming the western and higher eastward-dipping Paradise
Ridge is of considerable thickness, that forming the lower and practically
vertical-dipping eastern ridge is only one-third or one-fourth as thick.
So that, although a synclinal structure might be imagined between these
two ridges, there is not as much conglomerate exposed on the east side
of the supposed syncline as would be expected in the case of such a
structure. Another equally important point is this: A continuation of the
line of strike of the more eastern Paradise Ridge would reach a solitary
coarse conglomerate exposure at the west end of Sachuest Beach, with
strike N. 14° E., which has a dip of 40° E., but in order to agree with
the synclinal structure demanded northward its dip ought to be west. Less
important, because the exposures are not equally satisfactory, is the vertical
dip shown by the exposure east of the north end of the continuous eastward-
dipping line of exposures already described, where the dip is 50° E. The
dip of the more eastern exposure should be westward to agree with synclinal
structure in this region. The second, more eastern, ridge shows in places
evidences of local folding.
In view of all the facts observed it seems reasonable to suppose that the
Paradise ridges form a great eastward-dipping series of conglomerates on
the western side of a syncline. The eastern of the two ridges dips east-
ward only at the southern end. North of the reservoir the conglomerate
beds of this eastern ridge are affected by a local flexure traversing the
series a little diagonally, which has bent these beds downward and moder-
ately overturned them northward, so that the almost vertical but somewhat
westward dip of the eastern ridge along its southern end is changed to an
almost vertical but slightly eastward dip near its northern end, the dip of
50° E. in the field a considerable distance north of the second ridge, and
298 GEOLOGY OF THE NARRAGANSETT BASIN.
another of 40° E. on Sachuest Beacli, south of the ridge, remaining to show
the real structure of the series of which this eastern ridge forms a part.
At the north end of the western or principal ridge the lower eastward
dips show that the syncline is more shallow northward. The low dips
seem to continue northward, since the remaining conglomerate exposures
as far as the east-west road fail to bring up on end the interbedded sand-
stones, and so their dip can not be determined. North of the road, how-
ever, in a field a fifth of a mile west of the road corners, conglomerate is
exposed with a strike N. 30° E., dip 20° E., lower eastward. North of the
road corners above mentioned blue sandstone with a little conglomerate
dips low eastward, and seems to pitch southward. A sixth of a mile south-
ward, west of the angle of the road, similar sandstone is exposed in a field.
HANGI^TG KOCKS.
The Hanging Rocks, along the western side of Grardners Pond, form
the southern end of another great ridge of coarse conglomerate. The strike
of the conglomerate in the ridge is N. 16° E., dip 70° W., in some places
almost vertical. Overlying it on the western side, noi'thward, is a bluish, in
places shaly, sandstone. This Hanging Rock ridge of conglomerate is
about half a mile long. It seems to form the eastern side of a great
southward-pitching syncline, of which the Paradise Rocks form the western
side. Seen from one of the g-reat trap ridges in the central area of this
synclinal district, the topography favors such an interpretation of the series.
Immediately east of Hanging Rock, north of the bend at which the road
skirting it turns eastward, a low ridge of conglomerate is found, west of
the brook. Its dip seems to be steep eastward, nearly vertical. Other
exposures are found farther northward, west of the brook. East of the
brook is another low conglomerate ridge extending southward into Gardners
Pond and forming the eastern border of the narrow division of the pond
into which the brook empties. The strike of the main exposure here on
the west side is N. 16° E., dip from 80° W. to vertical. The fact that
this exposure lies east of the line of strike of the exposures farther north,
on the west side of the brook, which sometimes show eastward dips, should
be noted. Along the eastern side of this promontory, near its southern
end, the dip is about 60° E. This eastward dip continues to be shown
by the continuation of the eastern side of this line of exposure northward,
being 40° E. in the fields north of the road, the strike being N. 20° K.
HANGING EOOKS. 299
East of the strike of this line of outcrops, at its northern end, west of a farm-
house, is another exposure of conglomerate stx-iking N, 10° E., but dipping
80° E., and insignificant exposures are found southward from this last
exposure.
If now the series of exposures east of the main Hanging Rock ridge
be taken, and their dips be compared, it will be seen that there is a succes-
sion of steep, practically vertical, and of less inclined, eastward dips. This
might at first sight be taken as evidence of a series of anticlines and syn-
clines. But the ridge occuiTing immediately east of the brook which
empties southward into the pond, changes from a steep, practically vertical
dip near its southern end to a lower eastward dip on going northward, and
also to a lower eastward dip on going southeast to the edge of the promon-
tory on the pond. East of the northeast end of this ridge east of the brook
the steep eastward, nearly vertical dip comes in again. It is believed that
these conglomerates are not folded in anticlines and synclines, but that all
form parts of a steeply west-dipping series affected by flexures varying as
regards the dip along the strikes of the same beds, and apparently also vary-
ing in this regard in closely contiguous beds. This is a condition of things
not infrequently seen when a general synclinal structure has been brought
about in a series of harder rock separated by layers of softer material^
which permit of more or less sliding. Structures of this kind may be seen
on a smaller scale in connection with the folding at the north end of
Sachuest Neck.^
The Hanging Rocks and more eastern exposures are believed to be
the eastern side of a great syncline, of which the Paradise Rocks form the
western side. The folding of the Easton Point anticline on the west side
of this syncline is quite regular, and hence the eastern side of this syncline,
which forms the western side of the Paradise-Hanging Rock syncline, pre-
sents quite regularly only the eastward dips, except along the eastern ridge,
where very steep westward dips occur in places, as described. The anti-
cline on the eastern side of the Pai'adise-Hanging Rock syncline is
evidently the result of stronger folding, the dips from Smiths Beach to
Taggarts Ferry being often 70° E., and at the ferry vertical or 80° W.
' Dale, Crosby, and Barton regard the structure of the Hanging Rocks district as an anticline.
The conglomerate east of tbe Hanging Eoclis dips east, while the Hanging Rocks dip west. This
interpretation would demand the assumption that but a small part of the conglomerate on the western
side of tlie anticline is actually exposed.
300 GEOLOGY OF THE NAREAGANSETT BASIN.
On the west side of the Woods Castle-Black Point anticline the series in
the Hanging Rocks Valley is evidently somewhat overturned in places,
although the chief ridge, that of the Hanging Rocks, dips 80° W. The
result of the more accentuated folding, as indicated by the steeper dips, is
a violent contortion of the rocks, shown by the local rapid variation of dip,
due to local folding subsidiary to the more general synclinal folding which
determined the great structural features of the Carboniferous area along
the Hanging Rock Valley and Avestward. This syncline is believed to
pitch strongly southward.
The most northern outcrops of coarse conglomerate occur a little over
a mile from both Black Point and Taggarts Ferry, about three-quarters of
a mile west of the Sakonnet River, along the west and east sides of the
road. Here the strike is N. 3° E., dip 46° W., on the east side of the
road southward, changing to strike N. 15° E., dip 40° E., on the west side
of the road near the middle exposure, and dipping the same amount east at a
continuation of the middle exposure northward on the east side of the
road. This seems to represent the northern end of the syncline in the
coarse conglomerate bed, and lies about 60 to 80 feet above sea level.
Southward the base of the syncline pitches far beneath sea level.
PRB-CARBONIFEROUS AREA.
Between the eastern ridge of the Paradise conglomerates and the
Hanging Rock ridge of conglomerate lies an area of igneous rock and of
quartzite-schists which seems to be pre-Carboniferous. The most south-
western exposure of the hornblendic rock, possibly at the time of its injection
a coarse diabase, is found along the southern embankment of the reservoir,
at an angle near its middle line. The next exposure occurs at the northern
end of the reservoir, between the middle and the eastern creeks entering the
reservoir from that side. It there forms a ridge which can be traced north-
ward for about half a mile, and is evidently in line with the exposure south
of the reservoir. Bordering the east side of the reservoir is another, much
loftier and broader range of the igneous rock, almost half a mile long.
East of this lies a somewhat narrower ridge, at one point broken down and
permitting the formation of a glen between the main range of igneous rocks
westward and another high ridge lying to the eastward. This eastern ridge
lies directly west of the Hanging Rock coarse conglomerate with its over-
Ivino- bluish sandstone and more arreenish shalr varietv.
PKE OAliBO^IFEEOUS EOCKS OF PARADISE. 301
The igneous rock has evidently penetrated a great mass of quartzitic
schists similar to those foxind west of East Greenwich, north of Tiverton,
south of Common Fence Point, and elsewhere, and to a somewhat less
degree like the quartzitic schists or shales east of Browns Point. These
schists may be found well exposed in the area between the two main ranges
of the igneous rock east of the pond and on the promontory between the
middle and east creeks north of the reservoir. They were formerly also
well exposed on an island in the southeastern corner, now covered by the
reservoir. They occur also as fragments inclosed in the larger ridges of the
igneous rock and in the smaller exposures of the same material. Curiously
the strike and dip of the included fragments and of the larger masses of
the quartzitic schist penetrated by the trap dikes are so constant that a gen-
eral strike of N. 20° E. and a dip of 50° to 60°, sometimes 70°, W. will
sufficiently explain their general relations to one another. On the promon-
tory of trap rock north of the pond, however, it may be seen that this strike
is chiefly the direction of the plane of schistosity, the bedding being appar-
ently, at least in places, at variance with the same.
The igneous rock above referred to as cutting the pre-Carboniferous
whitish quartzitic rocks in the Paradise-Hanging Rock region shows, even
macroscopically, the presence of a crystalline structure. The rock is
composed chiefly of plagioclase and hornblende, both in a very advanced
state of decomposition. This combination would place the rock under the
heading of diorite, and here it is placed by Mr. George P. Merrill, who
first made a microscopical examination of these dike rocks. He makes,
however, the qualification that "it is, of course, possible that this horn-
blende may itself be secondary and that the perfectly fresh rock would
show augite; but this does not seem probable." If hornblende replaced
original augite, the trap rock would then be an altered diabase.
With this determination of the igneous character of the trap rocks of
the Paradise-Hanging Rock region in hand, Professors Crosby and Barton^
were the first to make a careful study of these dikes, and they state that in
no instance did the}^ " discover the slightest indication of a passage from
the dike rock to the [quartzitic] slate, but the two are always separated by
a perfectly sharp and definite line."
The trap occurs in parallel ridges running in the same direction as the
1 Proc. Boston Soc. Nat. Hist., Vol. XXIII, 1886, p. 32.5 et seq.
302 GEOLOGY OF THE NARRAGANSETT BASIN.
coarse conglomerate ridges. The largest of these are on the eastern side of
the region here described. The great ridge west of the Hanging Rock
ridge is composed almost entirely of trap, but shows toward the north, on
its eastern face, toward the upper portion of the ridge, a number of long
inclusions of the quartzitic slate which it in general intersects. This
quartzitic rock is also shown on the western side of the same trap ridge,
near its highest elevation; it also is exposed on the eastern side of the next
ridge westward, and probably once occupied the valley separating the
two ridges. This western ridge is also composed almost entirely of trap
rock, the dike rock forming the top and the entire western face of the
ridge. Toward the north a lower ridge of trap is found between the
other two. West of the western of the lofty trap ridges is the reservoir.
At a very low stage of the water in the reservon an island is exposed
which is composed chiefly of the quartzitic sandstone, but which also
shows trap on the western side. Crossing the eastern brook entering the
reservoir from the north, a trap dike is encountered, then quartzitic slate,
then more trap. Northward these trap exposures increase in elevation
and form the eastern side of a low ridge lying approximately along the
middle of the reservoir valley. Near the northern end of this region
inclusions of the quartzitic slate can be seen in the trap. The slate is found
also west of this trap ridge.
The Paradise-Hanging Rock valley is undoubtedly occupied alto-
gether b}^ the quartzitic slate, intersected by coarse trap, the quartzitic slate
forming the valleys and the trap the ridges. .
In the present state of knowledge on the subject, no place for these
quartzitic schists can be found in the Carboniferous series. They either
overlie or underlie these rocks, and owing to their resemblance to rocks else-
where with confidence adjudged pre-Carboniferous, they are also considered
older than Carboniferous, and are believed to have been left as a great
triangular mass, bounded east and west by fault planes along which the
Carboniferous strata dropped down. Whether the diabasic rock preceded
or anteceded the period of deposition of Carboniferous rocks is not known.
Attention should, however, be drawn in this connection to the frequency of
dike action in the pre-Carboniferous shales of the Newport Neck region,
and to a less degree in the green pre-Carboniferous rocks of Sachuest Neck
and in the Conanicut Carboniferous shale series.
All of these interpretations of the geological structure of the exposures
EASTONS POND. 303
of the Paradise and Hanging Rock series may seem rather forced, but they
appear to be the only ones consistent with knowledge obtained elsewhere
in the field, which rests on a more secure foundation. No eff'ort has been
spared to secure a more ready and simple explanation, but the exposures
are not sufficiently numerous and conclusive, and the interpreter is di-iven
to theorizing where more exposures would make this unnecessary.^
ISOLATED CONGLOMERATE EXPOSURES NEAR EASTONS POND AND
NORTHWARD.
On the west side of the Eastons Point anticline it will be remembered
that there is evidence of synclinal structure, and that at the east end of
Eastons Beach the dip is about 15° to 20° E
West of the northern half of Eastons Pond, below the greenhouses,
bluish sandstone, darker shaly rock, and some conglomeratic layers com-
posed of pebbles, not recalling the coarse conglomerate series, are found.
They do not seem to vary far from a horizontal position.
Three-quarters of a mile northward, in the field, north of a farmhouse
north of the east-west road, much coarser conglomerate is exposed, with
quartzitic pebbles of the Paradise Rock type up to 8 inches in length, but
usually only 3 to 4 inches long. It seems to be part of an anticlinal fold
pitching northward about 10° and trending N. 16° E. On the western
side the dip is about 15° W.
A somewhat similar conglomerate is exposed a mile northeastward,
west of the western road corners of a triangular plat of land formed by the
public ways. The pitch here seems to be also low northerly, the strike
being apparently N. 7° W., dip very low west, but the exposure is not
suitable for the exact determination of these features.
The precise relation of these exposures to the general shale series
northward and westward is not known.
According to the interpretation given by Professor Dale (loc. cit.), the
great Purgatory conglomerates overlie the Aquidneck shale series, but dip
under the Newport Cliff exposures. To the writer the cliff exposures appear
to belong to the horizon of the Sakonnet sandstones and the lower half of
the Purgatory conglomerates, though he does not know of any very con-
clusive evidence for either view.
' Consult, on the same area, T. Nelson Dale, Boston See. Nat. Hist., Vol. XXII, 1883, and Proc. New-
port Soc. Nat. Hist., 1885.
304 GEOLOGY OP THE NAKRAGANSETT BASIN.
MIANTONOMY HILL AND COASTERS HARBOR ISLAND CONGLOM-
ERATES.
MIANTONOMY HILL.
A little over a quarter of a mile south of the top of Miantonomy Hill
coarse conglomerate is exposed, south of a house along the edge of a field.
It is again exposed northwest of the house, trending northward. Northward
it forms the entire structure of Miantonomy Hill. Interbedded sandstone
along the entire northern margin of the hill shows the conglomerate to be
apparently horizontal from east to west, but in fact dipping southward at an
angle of about 15°. There is apparently a low eastward dip at the
northeast angle of the hill.
The pebbles of this conglomerate are of the largest size, at times more
than 2 feet long, and they have not been elongated. They are evidently of
the Purgatory type.
Northward, between Miantonomy and Beacon hills, there is exposed
considerable dark-blue sandstone, shaly in places, dipping low southward.
BEACON HILL.
On the summit of Beacon Hill more conglomerate is exposed. The
pebbles on the average are of much smaller size and usually do not exceed
8 inches in diameter. The series has evidently been slightly folded by
an east-west thrust, as may readily be detected by following the line
between the conglomerate and the overlying interbedded sandstone at the
north end of the hill summit. The pitch is again about 15° S., and the
westward dip on the northwest side of the hill suggests that the conglomer-
ate is here descending into the valley. The conglomerate of Beacon Hill
evidently underlies the much coarser conglomerate of Miantonomy Hill.
FIELD EXPOSURES.
In a field west of Miantonomy Hill and just east of the railroad is a
series of coarse conglomerate exposures, striking N. 8° W. and dipping
45° E. The most western exposure has smaller pebbles, the more eastern
ones larger pebbles, some of these attaining a length of IJ to 2 feet.
Fossil oboli were found in one of the pebbles. Interbedded sandstones
disclose the dip. This dip indicates a synclinal structure between these
CODD]NGT0:tT iSTECK. 305
exposures and those of Miantonomy and Beacon hills. The southward
pitch, so well shown on the hills named, indicates how it is possible to have
the regular dark-blue and black shale along the railroad cut north and
south of Coddington Cove along with a total disappearance of the conglom-
erate series. Anyone standing on the top of Beacon Hill, and knowing
the distribution of the shale series northward, can not fail to be convinced
that the coarse conglomerates overlie that series.
CODDINGTON NECK.
The bluish-black shale series underlies Coddington Neck. Almost
continuous exposures occur along the western side of Coddington Cove, and
form the two main hills of the neck. At tlie north end of the neck these
shales strike N.-S. and dip 70° .to 80° W. Farther west these dips are
less steep. About 225 feet southwest of the most northern point of the
neck fern-leaf impressions Avere found in the bluish-black shale. At the
northwestern angle of the neck coarse conglomerate appears, still dipping
westward, overlying conglomerate with medium-sized pebbles. Farther
along the coast southwestward, more conglomerate with medium-sized
pebbles is seen; then brownish sandstone, again the former conglomerate,
and then coarse conglomerate appear in succession, the second exposure of
coarse conglomerate appearing at the western angle of the shore where it
begins to turn southward. The dip of the coarse conglomerate here is very
steep eastward. In other words, a very compressed syncline has brought
down the base of the coarse conglomerate series. Southward from the
more southern conglomerate exposure, the bluish-black shale series is seen
to contain frequent narrow intercalations of a whitish sandy rock.
BISHOP ROCK.
The same series of blue-black and coaly black shales, with bands of
whiter rock, is exposed on the northwest side of Bishop Rock, striking N.
40° E. on the north side, toward Coddington Neck, and curving westward
and then southward so as to strike about N. 25° E. on the west side of the
rock. The series dips westward about 60°. Underlying it, southeastward,
is medium.-sized quartzitic conglomerate, and beneath that is coaly shale,
evidently much folded and contorted. Fragments of arkose and other
rocks appear in the coaly shale as though they were pebbles, but the
MON XXXIII 20
306 GEOLOGY OF THE NAEEAGAXSETT BASIN.
appearance of some of the larger fragments suggests that they once formed
continuous beds intercahxted in the coaly shale. In that case the occur-
rence of arkose in this shale is of interest. It will be remembered that
arkose is associated with coaly shales on Sachuest Neck. It is beheved
there to overlie a greenish shale and conglomerate, possibly comparable
with the Little Compton green shales. It derived the materials for the
arkose in part from the coarse-grained granites on the south and east.
The granite nearest to Bishop Rock is 2^ miles distant, at the southern
end of Jamestown, on Conanicut, and at the southern end of Newport Cliffs
and on the adjacent part of the neck. The nearest exposures of green
shales are on Goat Island, Rose Island, and Freebody Hill. Nowhere
can these rocks be brought in close relation with one another so that their
relative age may be determined. The arkose on Bishop Rock seems to
belong to a horizon not far from the coarse conglomerate on the western
side of Coddington Neck, and probably occur just beneath the same. Simi-
lar arkose occurs near the southern end of Coasters Harbor Island.
COASTERS HARBOR ISLAND.
The very coarse conglomerates, with pebbles often 1 foot and at times
2 feet long, so well shown on Miantonomy Hill, are again well shown on
Coasters Harbor Island. No elongation of the pebbles is observable here.
The strikes and dips are variable. The most southern exposure of conglom-
erate on the east side of the island has a strike N. 65° E., dip 40° to 50°
NW. North of a small indentation of the coast the strike remains N. 65°
E., but the dip becomes only 20° NW. Within a short distance north-
ward the strike changes to N. 80° W. and the dip becomes 60° NE., and
along the northeast coast the strike is N. 30° W. and at various locah-
ties the dip is 80° to 85° E. West of a small embayment the rocks of the
northern promontory of the island seem to be in part folded, and elsewhere
dip 80° W., striking N. 10° E. In an embayment west of this promon-
tory sandstone is exposed, the apparent dip, which may be cleavage, strik-
ing N. 35° E., dip southward. At the northwest angle of the island the
strike is N. 30° E., curving southward to N. 10° E. and N.-S., while
the dip is constantly eastward, about 40° E. northward, becoming less
southward. Southward carbonaceous sandstone and fine conglomerate are
faulted against the coarse conglomerate, which is almost horizontal, and
NEWPORT HARBOR ISLANDS. 307
then the strike suddenly becomes N. 80° W., dip 40° S., changing to N. 20°
W., dip irregularly south, after which carbonaceous shales and sandstones
make their appearance, occasionally showing conglomerate, the strike being
approximately N.-S., and the dip 45° E. Southward, along the southwestern
border of the main body of the island, coarse conglomerate is seen again,
striking at first N. 40° E., dip 40° to 20° E.; then, as the shore turns southeast,
the strike becomes N. 45° W., then N. 10° W., dip low east, the conglom-
erate becoming less coarse. Farther southward dips of 30° E. are noticed,
and then, as the shore turns southward, green fissile shales, similar to the
Conanicut shales, make their appearance.
At the southwest angle of this tongue of the island, arkose with thin
layers of carbonaceous shale outcrop, with strike E.-W., dip 40° N. The
rock south of the arkose and forming the southern end of the island is
a greenish rock, which provisional^ is here placed with the Newport Neck
series of shales. Near the arkose it strikes N. 30° W., dip 40° E., and east-
ward N. 50° W., dip 25° E. Similar arkose is found on Bishop Rock and
on Rose Island.
The coarse conglomerates of Coasters Harbor Island are evidently to
be associated with the Miantonomy Hill conglomerate. The occurrence of
almost constant eastward dips along the western side of the island is to be
emphasized. The discussion as to the relationship of these conglomerates
to the green shales at the south end of the island is deferred until the
Harbor Islands are taken up.
NEWPORT HARBOR ISLANDS.
In this connection the description of the occurrence of the green shales
at the southern end of Coasters Harbor Island should be again noted. Off
the shore to the south of the island additional exposures of the green shales
occur. They are considered to be of pre-Carboniferous age.
GULL ROCKS.
The main rock is occupied by a light-house. The pre-Carboniferous
green shale here includes a more sandy, coarser variety of that rock, dipping
about 20° N. A short distance southward is another exposure of similar
nature, also dipping northward.
308 GEOLOGY OF THE iS^ARRAGANSBTT BASIK
ROSE ISLAND.
The main body of Rose Island, all except the narrow tongue projecting
northward, is composed of the greenish rock already mentioned as occurring
on the Gull Rocks anc" at the south end of Coasters Harbor Island. The
strike, as heretofore, is approximately E.-W., the dip 15° to 20° N.
Some of the layers are coarser and resemble sandstone, while others are
tinted purplish, as at Gull Island light-house. They are considered to be
of pre-Carboniferous age.
North of the green series of rocks on the eastern side of Rose Island
arkose appears. It seems to strike north-south and dips almost vertically.
Farther north, forming the lunate extension of the tongue, are (ioaly sand-
stone and shale, with strike N. 25° E. and very steep dip, perhaps 70° W.
On the western side arkose layers occur also southward toward the contact
with the green shales, green shales coming in contact with the arkose as
though brought together by a fault.^ Reference has already been made to
the arkose on Bishop Rock and Coasters Harbor Island.
CONANICUT ISLAND.
The arkose northwest of the granite area east of Mackerel Cove has
already been described. Farther eastward, also north of the granite,
occurs a pre-Carboniferous greenish rock, here called the Diunpling rock.
LINE OF SEPARATION BETWEEN CARBONIFEROUS AND PRE-CARBONIFEROUS
ROCKS.
If now the northern line of outcrop of the western part of the granite
and the pre-Carboniferous greenish Dumpling rock farther eastward on
Conanicut be connected with the northern exposures of the green shales on
Rose Island, the most northern exposures of green shales on Gull Rock
Island, and the most northern of the green shales exposed along the southern
end of Coasters Harbor Island, east of the arkose exposure, then it will be
noticed that arkose occurs immediately north of this line at Mackerel Cove,
Conanicut, on the southern end of the tongue of land extending north from
Rose Island, and at the southwest corner of the tongue of land at the south-
' Prof. T. Nelson Dale suggests that uncoil form ities betvreeu tbe Cambrian and Carboniferous are
quite natural. There may be an uuconforniity here, but the abrupt linear contact between the arkose
and the green shale, with the very marked variance between their dips and strikes, seems to exceed
that of ordinary uuconformities. There is no direct evidence that the Carboniferous arkose is resting
upon the eroded surface of the Cambrian shale.
GOAT ISLAND AND LITTLE LIME ROCK. 309
ern end of Coasters Harbor Island. The arkose is of Carboniferous age.
The greenish rocks south of this hne are supposed to be of pre-Carbon-
iferous age.
In the hght of this interpretation attention may be called to the facts
that a north-south line along the middle of Mackerel Cove probably
separates the pre-Carboniferous granite from the. Carboniferous Conani-
cut shales on the westward, and also that a line extending along the
western margin of the land, just offshore from Coasters Harbor Island, to
the end of Long Wharf, and thence more east of south, east of the Spindle
or Little Lime Rock to the southeast corner of Newport Harbor, then
southeast, east of the granite exposures in Morton Park, south of Newport,
and along the middle of Almys Pond, represents the dividing line between
the pre-Carboniferous rocks on the west and the Carboniferous series on
the east of this line. Thence the line extends eastward north of Sheep
Point. All of these lines are believed to be due to faulting.
GOAT ISLAND AND LITTLE LIME ROCK.
The pre-Carboniferous green shales^ have been reached in deep wells
on Goat Island, and they occur on Spindle or Little Lime Rock, and they
occur again as a series of rocks following each other in a north-south direc-
tion which are exposed at low tide sotitheast of Lime Rock. The dip and
strike of these exposures were not carefully investigated, there being no
means at hand of distinguishing cleavage from real stratification.
FORT GREENE.
South of Fort Greene Park carbonaceous black shales are well exposed
along the shore. They are banded here with thin layers of a whiter,
sandy rock, recalling the thicker interbedded white rock on Bishop Rock
and on the west side of Coddington Neck. Thin seams of coal, or at least
of very coaly shale, are said to have been struck at various times in the
cemetery a quarter of a mile east of Fort Greene Park.
MORTON PARK AND SOUTHWARD.
Granite is well exposed in the western half of Morton Park. Toward
the southeastern end of the grounds sandstone and blue-black slialy rock
are seen striking east of north and dipping steeply westward. A better set
' The author does not distingtiish between shales and slates or phyllites in this part of the report.
310 GEOLOGY OF THE NARRAGANSETT BASIN.
of exposures occurs half a mile southward, east of Almys Pond. Here
sandstone, shaly sandstone, and conglomerate are interbedded. The con-
glomerate contains medium-sized pebbles of a quartzitic rock. Here also
the strike is a little east of north and the dip very steep westward.
NORTHEAST LINES OF POSSIBLE FAULTING.
It may be noticed that a line connecting the most northern exposure
of the greenish Sheep Point rock, along the eastern end of Bailey Beach, with
its most northern exposure on the east side of Newport, north of Sheep
Point, takes a northeast direction, and north of this line lie the Carbonifer-
ous rocks of the Newport Cliffs, evidently faulted against the older
series. Moreover, along the northeasterly trend of the coast forming the
southern border of Newport Harbor, the pre-Carboniferous green shale
series, elsewhere called the pre-Carboniferous green shale of Newport Neck,
occurs at several localities. Little Lime Rock and the series of green shales
southeast of that locality have already been mentioned. Lime Rock itself
belongs to this shale series, although itself composed of limestone.
The promontory a quarter of a mile southwest of Lime Rock, con-
sisting of green shale and limestone, and the similar exposure northeast of
the stables on the southwest side of Brentons Cove belong to the same
shale series.
On the other hand, the rocks immediately south of the exposures just
mentioned, which form the neck proper, are granite eastward, and a green-
ish and purplish fine-grained rock of uncertain character, looking like
argillite, westward, as will be seen from the map, or from the description of
the rocks forming the neck.
CARBO]^fIFEROUS KOCKS ALOIffG THE NEAVPORT CLIFFS.
The discussion of the series of rocks forming the cliffs at Newport has
been left to the last, since least is known about them. It was intended to
prepare a careful detailed section of these beds, but considering the small
amount of time at the writer's disposal and the inaccessibility of these
rocks except at low tide, it was decided that the time required could be
more profitably employed elsewhere. This was especially the case since
the cliff exposures could not be definitely brought into relation with others
of known stratigraphic position.
NEWPORT CLIFFS. 311
The section along the chffs at Newport, from Easton's Beach to the
Forty Steps, mclucles about 175 feet of rock, the strike being, in general,
north-south, and the dip variable westward, but averaging 45° W. The fol-
lowino- notes will give an idea of the section disclosed: Southward from
Eastons Beach, going upward in the section, 3 feet of coaly shale, 29 feet
of sandstone with shaly layers, dip 20° W.; 4 feet of conglomerate with
pebbles up to 4 inches, dip 45° W., and 32 feet of sandstone. Thence,
going down in the series, the conglomerate and the sandstone, containing
some conglomerate layers, and dipping 50° W., are passed again. Beneath
occur 19 feet of coaly black shale, containing impressions of fern leaves,
15 feet of conglomerate with pebbles up to 4 inches in diameter, 22 feet of
sandstone, and an unknown thickness of carbonaceous shaly sandstone,
disappearing seaward, these last being the lowest rocks exposed along the
cliff. Southward, in ascending order, the cliffs expose 20 feet of con-
glomerate and 23 feet of shaly or fine-grained sandstone, dipping 80° W.
Southward, in descending order, the conglomerate occurs again. Then in
ascending order are found again the coaly shale and sandstone; then 7 feet
of conglomerate, 11 feet of shaly sandstone and coaly shale, 11 feet of
cono-lomerate, 40 feet of carbonaceous sandstone and coaly shale, 8 feet
of conglomerate, 27 feet of dark carbonaceous shaly sandstone, and high in
the bank, just before reaching the Forty Steps, and again on the south side
of the steps, a layer of conglomerate. At the steps the dip has become
very low eastward, the pitch being plainly southward, about 15°.
The total thickness of Carboniferous rocks south of Forty Steps does
not exceed 225 feet.
The conglomerate at the Forty Steps is 11 feet thick. Overlying it
are, in ascending order: 11 feet of black shale and gray sandstone, almost
horizontal; 11 feet of conglomerate, west of a fault, dip 40° W.; 11 feet of
sandstone and shale, 5 feet of conglomerate, dip steep west; 24 feet of
brownish shaly rock; more faulting; 9 feet of conglomerate, some of the
pebbles being a foot long; more faulting; 13 feet of coaly shale, having a
steep west dip.
After the coarse conglomerate with large pebbles comes in, a short
distance south of the Forty Steps, layers of very coarse conglomerate are
seen all along the shore as far as Oclu-e Point. It is probable that a care-
ful study of the section along this part of the coast would show that there
312 GEOLOGY OF THE NAERAGANSETT BASIN.
are only a few layers of very coarse conglomerate present, but that these
extend for a long distance along the shore, their continuit}' being inter-
rupted by small faults. A detailed description of the southern part of this
section, containing the coarse conglomerate layers, is of little value until
the effect of the faulting has been clearly determined. In a. general way
it may be stated that the lower coarse conglomerate layers alternate with
coaly shale and sandstone beds, as do the lower conglomerate layers
containing relatively smaller pebbles north of the Forty Steps. The
upper coarse conglomerate beds are associated with a series of greenish or
brownish-green sandstones and shales, which are best exposed farther
west and up the cliffs in the recesses of the shore north of Ochre Point.
At the promontory south of the Forty Steps the rocks dip low east.
In the recess of the shore southward the dip is 40° W. At the next
promontory southward the dip is again very low west, and in the recess
southward the dip is steeper west again. Southward the faults become
more frequent and the steep western dips are more common.
The coarse conglomerates and the associated greenish shales and sand-
stones which occur higher in the series, and which are exposed in the
recesses of the shore northeast of the Cornelius Vanderbilt mansion, are
exposed all along the northern shore of the cove west of Ochre Point. If
the rocks be here carefully examined at low tide, the conglomerate layers
will be found to be usually not thick, but they can at times be followed for
considerable distances along the shore. They show the presence of vari-
ous small anticlines and synclines, especially near Ochre Point, and also
east of an observation hoiise upon the sea wall farther westward. The
series in general, however, is evidently almost horizontal dipping as a
whole very low westward.
Along the northern side of this cove a few of the shale layers asso-
ciated with the coarse conglomerate are in places black rather than green,
especially near the western side of this shore of the cove.
The total thickness of the formation south of the Fort}^ Steps does
not seem to exceed 225 feet, due allowance being made for faulting, so that
the total section of the chff series so far seems to be about 400 feet. The
most striking geological feature of the series is the southward pitch of the
folds. This is often very low, but at times becomes very steep southward,
especially at the Forty Steps, and at another promontory exposing coaly
GEOLOGICAL POSITION OF NEWPORT CLIFF EOCKS. 313
sandstone and shale farther southward, where the ^^itch must be at least
15° S. This southward pitch is again well seen along the northern margin
of the cove, west of Oclu"e Point, where, however, it is very low south. It
continues to be shown at the northwestern angle of the cove.
The southward pitch of the folded series last described would certainly
carry it beneath the black coaly shale series exposed along the western
side of the cove almost as far south as Sheep Point. This series of coaly
shales and black carbonaceous sandstones contains abundant fern leaves.
It strikes approximately north-south and dips steeply westward, but near
its northern end it looks very much as though it overlies the green
coarse conglomerate series forming the north side of the cove. Arkose is
found in the northwestern angle of the cove. Its association with coaly
shale recalls similar exposures on Sachuest Neck. There may be faulting
here.
When the very marked southward pitch of the cliff series of conglom-
erates is considered in connection with the marked southward pitch of the
Eastons Point anticline and the similar pitch of the rocks on Miantonomy
and Beacon hills, it seems as though the cliff conglomerates mig-ht repre-
sent a southern extension of the coarse conglomerates of the last-named
localities and a westward continuation of the Purgatory conglomerate.
The failure of the coarse conglomerate to crop out along the western hill
slopes of Newport and at points southeast of the Miantonomy exposures is,
however, difficult to explain if this be the structure. The conglomerate
layers in the sandstone east of Almys Pond are hardly satisfactory evidence
of the former continuity of the coarse conglomerates between Eastons
Point, the Newport Cliff's, and Miantonomy Hill. In any event the New-
port Cliffs would represent only the basal part of the coarse conglomerate
section. The Fort Grreene and the Newport Cemetery coslj shales seem to
belong beneath the coarse conglomerate stratigraphically.
Newport itself seems to be underlain by strata belonging to the Aqtiid-
neck series (see footnote on page 372). If this be true the Newport Cliffs
may represent a section formed by the sharp synclinal infolding of rocks
along the trend of the cliffs. This synclinal structure was accompanied by
considerable subsidiary folding, and involved the lower part of the conglom-
erate series. A similar strong axis of folding seems to have been present
off the western side of Codding'ton Point and Coasters Harbor Island.
314 GEOLOGY OF THE NARRAGANSETT BASIN.
Southward it seems to have ended in a fault, and both systems of infolding
seem to have been accompanied by much subsidiarj- folding and faulting.
Fossil ferns are found in the carbonaceous shales north of Sheep Point,
especially at the promontories a little over a quarter of a mile north of that
point. Fossil oboli occur in pebbles at various points a short distance
north of Ochre Point.
XBWPOKT jV^ECK AND SOUTHEEX CLIFF ROCKS.
GREENISH ROCK IN THE CLIFFS SOUTHWEST OF SHEEP POINT.
From the western side of the cove west of Ochre Point, along the
shore almost as far as Sheep Point, extends a series of black coaly shales,
having a general strike parallel to the shore and dipping westward at vari-
ous angles averaging about 50°. A short distance north of Sheep Point
a greenish rock occurs, whose nearest outcrops are within a few feet of the
coaly shale; but while the general trend of the black shales is about N. 20°
E , the hne of contact between the shales and the green rock runs about
N. 45° E., as near as can be determined, and nearest the line of contact the
shales are much crumpled and the green rock has been so much sheared
that it slightly resembles a shale. At the southern end of the point the
shearing has ceased and the rock is seen to be in reality massive. Several
hundi-ed feet south of Sheep Point, at one of the projecting angles of the
shore, the greenish rock has included a rather large mass of a rock which is
bluish and very fine grained when fractured, but which has a whiter and a
more stratified appearance where subjected to weathering. Macroscopically
it therefore has the appearance of a stratified rock much contorted and cleft,
the crevices being penetrated by the greenish rock. Fragments of a similar
rock occur farther southward and present at times an appearance very much
like that of a stratified rock. Their nature can be determined only by micro-
scopic examination. Dikes of a whitish or faintly pinkish aplite are also not
uncommon, althougli occurring more commonly in the granite area farther
southward. In places the greenish rock presents the appearance of flow
structure. About three-eighths of a mile south of Sheep Point the greenish
rock is abruptly terminated by contact with a coarse-grained granite with
large phenocrysts of feldspar. The greenish rock here has a more evident
granular structure than usual and has the appearance of having once con-
GRANITE OF jSTEWPOET CLIFFS. 315
tained numerous cavities toward the contact, the cavities having later been
filled with a greenish mineral. This occurrence of apparently amygdalar
structure is itself suggestive of the igneous origin of the greenish rock.
But it may result from replacement of contact minerals originally due to
the intrusion of the great granite mass into the greenish rock.
GRANITE AREA AT THE SOUTH END OF THE CLIFFS.
The granite nearer low-tide mark is in actual contact with the greenish
rock, maintaining its coarse grain and the large size of its phenocrysts to
the contact. Farther from low tide, somewhat nearer the cliff walk, a
band of the pinkish fine-grained aplitic rock already mentioned intervenes,
the granite terminating abruptly against this rock, preserving the coarseness
of its grain and the large phenocrysts as far as the actual contact with the
pink aplite. The pink aplite at this point begins with a much finer
grain, and preserves this to its actual contact with the green rock. The
width of this band of pink aplite is 6 to 8 inches. Toward the sea it
partly includes fragments of the greenish rock between its mass and the
granite. Nearer shore it enters the granite mass at one point with a less
sharp contact, allowing the granite to come in contact with the green rock.
The pinkish aplite penetrates the greenish rock in dikes along the shore,
one of these dikes being much coarser in grain and showing more granitic
character, ha^dng apparently possessed both macroscopic feldspar and horn-
blende, but no phenocrysts, and not attaining the coarseness of grain of the
main granite mass. Some of these facts suggest that the granite is more
recent than the greenish rock. Nothing definite can be stated. In many
places the granite is itself frequently cut by the pinkish aplite. The
most northern exposure of the granite on the east shore is a little north of
the great bend where the southerly trend of the shore from Sheep Point
changes to the more rugged southwestern trend of the shore toward Cog-
geshalls Point. Thence it occupies the entire line of the shore as far as
Baileys Beach, south of Almys Pond.
A greenish rock, appearing like a dike, occurs in the most northern
exposure of the granite just before reaching the beach. Another greenish
rock, parallel to this, contains brecciated fragments — probably of the
same general mass, but looking whiter in consequence of weathering —
and also one pebble of undoubted quartzite. At the eastern end of the
316 GEOLOGY OF THE IS^ARKAGANSETT BASlIy\
beach there occurs an additional jnass of the greenish igneous rock, trav-
ersed in all directions by whitish streaks. This is probably a continuation
of the greenish rock from the eastern shore, near Sheep Point.
GRANITE AREA ON EASTERN NEWPORT NECK.
At the western end of the beach, south of Almys Pond, is found a
reddish granite, to a certain extent resembling the groundmass of the por-
phyritic granite already described, but lacking phenocrysts. Toward Lily
Pond the granite has changed from bright red to a much darker red, due to
the presence of an abundance of some darker mineral. These granites are
frequently cut by the pinkish fine-grained aplite, whose character as a dike
rock is unquestionable in all of the more western exposures. This second
granite area includes all of the rock between Almy's and Lily ponds, the
hill immediately west of Lily Pond, and tlience northward as far as the
southern margin of the harbor at Newport, excepting perhaps a narrow
border along the shore, which seems to be made up of greenish shales similar
to those found elsewhere about the harbor. It occurs also as a medium-
coarse granite north of Almys Pond, in the western part of Morton Park.
GREENISH AND PURPLISH ARGILLITIC ROCK OF MIDDLE NEWPORT NECK.
West of the granite area, as far as Brentons Cove, the western side of
Rocky Farm, and Prices Neck, occurs a fine-grained rock, varying in color
from green to dark purjjle, in places epidotic, which has usually been called
an argillite. It contains traces of banding very similar to stratification, but
which might be interpreted as flow structure. In the northwestern part of
this area Prof T. Nelson Dale found a fragment of undoubted quartz-
porphyry embedded apparently in a cement composed of clastic material.
This would indicate that at least a part of the area was of sedimentary
origin. This rock is closely related to the Dumpling Rock and the greenish
rock southwest of Sheep Point.
PRE-CARBONIFEROUS GREEN AND PURPLE SHALES OF WESTERN NEWPORT
NECK.
The western part of Newport Neck, including all the area west of a
line drawn through the marshes from the western side of Prices Neck to
the southern end of Brentons Cove, is occupied bj^ a series of shales.
WESTERN END OF NEWPORT NECK. 317
Their usual color is greenish, and very frequently whitish; more sandy, thin
layers are interbedded, giving the rock a banded appearance. This banded
character is well seen at various points on the east side of Brentons Point.
Sometimes the rock is rather quartzitic and is cleaved like the rock on the
hill east of Browns Point, east of Sakonnet River; one locality of this
kind is found along the east side of the road leading northward- into the
Fort Adams grounds and southwest of Brentons Cove. Not infrequently
the shales are purphsh in color, and where this is the case thin layers of
limestone are often intercalated in the shales. The same feature was noted
in the Little Compton shales, and suggests the identity of these shales.
Calcitic layers not being known from undoubted Carboniferous rocks, nor
having been found elsewhere in the field, suggests that the Brenton Point
shales are of pre-Carboniferous age.
Layers of calcite are especially numerous around the vicinity of Pirates
Cave and the shore just south of the irregular headland a quarter of a mile
southeast of Castle Hill. Along the summit of Castle Hill some masses of
limestone occur, but it is not certain whether the material is in situ. Around
Brentons Cove, however, these interbedded calcitic layers are thicker and
apparently more common.
The average strike of the above-described shales is N.-S., and the dip
30° to 40° E. However, on the southern and western shores of Brentons
Point the strike is frequently N. 30° W., varying at times to N. 70° W.,
and the dip occasionally becomes almost horizontal, and near the southwest
end of Brentons Point and north of Pirates Cave becomes locally even
westward. The most northern exposure of the green shales on the neck
is south of the wharves on the east side of Fort Adams. A sixth of a
mile south of the wharves, at a prominent angle of the shore, the green
shale contains thick limestone layers.
The existence of these limestone beds in tlie green shale series is of
importance, since nothing similar occurs in the undoubted Carboniferous
rocks. A hmestone bed is found northeast of the stables on the prominent
angle of the shore at the southwest side of Brentons Cove. It strikes about
N. 10° E. and dips steeply eastward. A quarter of a mile northward, near
Fort Adams, the hmestone occurs again, as already mentioned. Here it is
much crumpled, but seems in general to strike N. 70° E., dip southward.
318 GEOLOGY OF THE NARRAGANSETT BASIN.
A much thicker bed forms the two exposm-es at the Lime Rock hght-house,
whose strike seems to be approximately east-west, dip steep southward.
A bed of hmestone more nearly agreeing in thickness with the two occur-
rences above described is found on the promontory a quarter of a mile
southwest of Lime Rock. Here again it is prominently associated with the
green shale series, and strikes N. 50° to 60° E. and dips steeply northward.
Limestone beds are also said to have been struck in penetrating the green
shales which underlie Goat Island. These thicker calcite beds, which occur
along the southern border of Newport Harbor, are in places coarsely
crystalline in consequence of metamorphism, but usually show a fine grain,
and, though white within, weather to a peculiar light-brown color. The
thinner beds of calcite, however, south of Pirates Cave and in the Little
Compton shales are usually tinted with pink or reddish purple.
So far, in all eastern Massachusetts and Rhode Island, only two forma-
tions of Paleozoic age have been discovered, the Cambrian and the Car-
boniferous. The Carboniferous is nowhere known to contain true limestone
beds of sedimentary origin.^ The Olenellus Cambrian at almost all of the
localities where it is known to occur in these States contains limestone inter-
bedded with shales, resembling especially the thinner limestone beds of the
green and purple shale series in the southern Narragansett Bay region. In
view of these facts search for fossils was made in these southern localities,
but without success. The determination of the age of these shales as pre-
Carboniferous therefore rests upon two facts — the presence of limestone
layers and the entire absence of carbonaceous material in any of these beds.
If, in addition, the relations of the arkose to the green shale series at
Sachuest Neck be taken into account, and the occurrence of the arkoses at
the line of contact between the green shale series of supposed pre-Car-
boniferous age and the Carboniferous rocks on Conanicut, Rose Island, and
Coasters Harbor Island be considered, an assumption of the pre-Carbonif-
erous character of the green shale series affords a more ready explanation of
the cause of its present distribution, faults having thrown pre-Carboniferous
rocks upward on the south side of the faults, against higher-lying Carbonif-
erous rocks.
' As will be seen from Mr. Woodworth's part of this monograph, there are limestone deposits in
the Wamsutta series, but these are probably of secondary origin, owing their formation to the injec-
tion of igneous rooks in the area in which they are found. — N. S. S.
CODDINGTON COVE TO LAWTONS VALLEY. 319
SHALE SERIES FROM CODDINGTON COVE TO LAWTOKS VALLEY.
In the railway cut southeast of Coddington Cove the bluish-black shale
is exposed for a quarter of a mile. The cleavage dips 15° to 20° W.
In the most eastern part of the indentation at Coddington Cove black shale
is exposed again, the cleavage dipping 10° to 20° E. Three-quarters of a
mile northward, south of the angle of the shore directly east of Gould
Island light-house, the dark carbonaceous, often black, shale is seen in the
bank. It is much cleaved, the dip of the cleavage being low eastward.
Northward, in the concave curve of the shore, gray-blue sandstone is
interbedded with the coaly shale. The cleavage still dips only 5° to 10°
E., but the real stratification shows strike N. 21° E., dip 25° to 30° E. At
the north end of this cove the most western part of the shore line shows
more of the carbonaceous sandstone interbedded with coaly shale; strike
N. 12° W., dip about 60° E. A few fern-leaf impressions occur in the
shale here. Over the sandstone lies more of the coaly shale. The sand-
stone and shale continue to be exposed for half a mile northward, the strike
changing at the north end to N.-S., dip 50° E. The cleavage is low
west. Along the railroad southward, near the north end of the cut, greenish
shale and sandstone occur, the latter including thin layers of fine conglom-
erate. These greenish rocks evidently belong in the blue shale series,
but overlie the shore exposures. Along the east- west road northward,
nearly half a mile from shore, black shale is exposed. Where the next
creek northward crosses the road from Newport to Bristol Ferry, the
greenish-blue shale series is exposed in the creek bed west of the road. A
little south of the mouth of this creek coaly shale and sandstone are found
in numerous fragments in the banks, as though occurring in situ farther
back from the face.
East of Carrs Point and south of Lawtons Valley the north end of
the railway cut shows coaly shale and carbonaceous sandstone; strike
N. 15° E., dip 15° E., as far as could be determined; the exposure is not
satisfactory. The blue shale series is exposed along Lawtons Valley,
about half a mile south of the point where this valley crosses the Newport
raod, and where the east-west road leaves the Newport road eastward
for the Glen region on the east side of Aquidneck. Up the road eastward
the blue-black shales are exposed as far as the brow of the hill. A little
320 GEOLOGY OF THE NAREAGANSETT BASIN.
nortliward from this road, along- the Newport road, the bkie-black ' shale
fragments, apparently almost in sitn, show freqnent fern-leaf impressions.
Farther northward, in the roadside, greenish shale occurs. These green
shales are seen again east of the road on the northwestern side and along
the summit of tlie hill, and are overlain on the eastern side of the hill by
fine-grained grayish-green sandstone striking about N.-S. and dipping 30°
to 40" E. This sandstone is exposed again northward along the strike on
the west side of the road. This exposure serves to confirm the exadence
of the general eastward dip of the rocks along the western side of the
island, a feature so much better shown to the northward. The dark green-
ish-blue shales are also well exposed where Lawtons Valley crosses the
east-west road leading toward the Glen.
GREEXISH-BIjUE SHAIjES of SLATE HILL AND SOUTIIAVARD.
Along the East Newport road, east of the highest part of Slate Hill,
bluish shale tinged with green is exposed west of the road. A quarter of
a mile southward the shale, here colored dark blue, at one point verging
to black, occurs interstratified with sandstone. The strike is N. 15° E., dip
apparently low E., about 10°. Half a mile southwest along the road,
where it begins to descend the hill more rapidly, the greenish-blue shale is
exposed, and tlii-ee-eighths of a mile farther on it is seen for the last time
on the west side of the road. The isolated conglomerate exposm-e thi-ee-
quarters of a mile farther southwest has already been mentioned.
SHALE SERIES NORTH OF LAWTONS VALLEY.
SHORE EXPOSURES NORTH OF COGGESHALL POINT.
Coaly shale is exposed along the shore tlii-ee-quarters of a mile north
of Portsmouth Grove Station and continues northward. Near Corys Lane
fine-grained sandstone overlies the shale and contains plant impressions.
North of Corys Lane the shore offers material for a detailed partial section
as follows, in descending order, going northward :
Section north of Corys Lane.
Feet.
Fine sandstone 13
Black coaly shale, containing Sphenophyllum equisetiformis, Annularia longifolia,
and large fern- frond impressions 9
Sandstones, in j)laces somewhat coarse 7
PORTSMOUTH MINE, 321
Section north of Corys Lane — Continued.
Feet-
Black coaly shale 4=
Sandstone ■ 10
Coaly bed, with low eastward dip 20
Black coaly shale 4
Black shale and very tine-grained sandstone, Tfith low eastward dip (about 10°),
showing abundant traces of plant remains 9
Fine-grained sandstone 4
Coaly shale and fine-grained sandy rock, striking about parallel to the shore and
dipping 20° B 8
Coaly shale 17
Black shale, dipping 10° to 15° E 15
Not exposed 5
Shaly sandy rock 1
Coaly shale 9
The section terminates a little over half a mile south of Portsmouth
Mine Station, south of the mouth of the creek.
PORTSMOUTH MINE AND NORTHEASTWARD.
At the Portsmouth mine (see footnote on page 381) three beds of
coal were formerly mined. The dip was about 35° SE., the strike having
changed here considerably toward the east. The old dump shows coal,
black shaly slate, and black sandstone, sheared until a part of this is also
schistose. Calamites, Anmdaria longifolia, and many fern-leaf impressions
occur here.
Three-quarters of a mile northeastward, on the hillside east of the
railroad, a coal seam was also once opened, and the dump shows the same
kind of rocks as at the Portsmouth mine.
A quarter of a mile south of the Bristol Ferry hotel the roadside shows
coaly shale, striking apparently N. 35° E., dip 50° E.; not satisfactory.
A little south of the last exposure a road turns off eastward, toward
the south end of Town Pond. Here carbonaceous sandstone, some of the
layers coarse, contains fragments of carbonaceous shale, much crumpled,
apparently by a force acting east-west.
A boring in Portsmouth, Rhode Island, examined by Mr. Collier Cobb,
gave the following record as regards succession and thickness, but no
account is taken of possible reduplication by faulting or folding. In this
table argillaceous strata in superposition and variously denominated argil-
MON XXXIII 21
322 GEOLOGY OF THE NAEEAGANSETT BASIN".
lite, slate, and shale fire clay in tlie original record have been grouped
together as a single bed under the name argillite:
Record of boring in Portsmouth^ Rhode Island.
Feet. Inches.
1. Below casing, fire clay 13 1
2. Argillite, dark colored, growing lighter aud becomiug friable downward . 9 4
3. Argillite, in upjier part slaty, banded and light gray, crossed by seams
of epidote and magnetite 8 7
4. Gray sandstone 8
5. Drab slate 1 0
6. Gray sandstone, containing calcite 3 11
7. Brecciated slate 1 0
8. Carbonaceous argillite 2 1
9. Goal, with quartz impurities, brecciated 3 0
10. Carbonaceous argillite 2 6
11. Coal, some quartz in uppermost part 3 9
12. Slate 6
13. Goal, considered good up to 49 feet 10 inches 2 9
14. Quartz aud slate breccia 2
15. Goal, filled with fine particles of calcite 3 0
16. Argillite 8 1
17. Argillaceous slate 2 4
IS. Brecciated carbonaceous matter, containing quartz and some magnetite . 4
19. Argillaceous shale 2 2
20. Coal, with quartz and iron pyrite 3
21. Argillaceous shale 4 7
22. Highly carbonaceous shale 6 2
23. Quartz, with fire clay 5 8
24. Fire clay, like top of hole 1 3
25. Argillaceous shale 2 8
26. Fine sandstone 4
27. Quartz ; probably chlorite gives the green color to a part of the quartz. 3
28. Argillite, dip 24° 5
29. Sandstone, showing feldspar and chloritic development 6 0
30. Goal, containing magnetite 1
31. Quartz, containing chlorite and pyrite 1
32. Sandstone 9 3
33. Argillite, brecciated 3 6
34. Sandstone 13 7
35. Quartz vein 1
36. Sandstone, discolored by iron oxide, with quartz veins, feldspar, and
chlorite 16 5
37. Carbonaceous shale 4 1
38. Slate, drab in color, with iron pyrite 4 6
39. Carbonaceous shale, with quartz veins 2
40. Black shale, with small quartz veins and iron pyrite 4 7
EEGOED OF BOEING IN POETSMOUTH. 323
Feet. Inches.
41. Argillite 6
42. Sbale 7 0
43. Sbale, black and carbonaceous, contaius some quartz 2 0
44. Sandstone 4 8
45. Sandstone, more compact and modern than above 1 1
46. Sandstone 6
47. Sandstone 1 0
48. Slate, with crystals of iron pyrite 3 0
49. Quartz vein -_ - 1
50. Slate, crossed by small veins of quartz, calcite, and iron pyrite 9 4
51. Sandstone, dark and tine grained 4 11
52. Slate, very hard and fine grained 8 6
53. Sandstone, hard and fine grained 1 3
54. Shale, hard and black 7 4
55. Coal, a highly carbonaceous graphitic bed 2 1
56. Slate, hard - 7 11
57. Quartz vein 1
58. Slate, hard 3 8
59. Shale, carbonaceous 5 8
60. Shale, sandy 4 6
01. Slate, hard and black, carbonaceous 5
62. Slate, hard, black, and sandy 7 11
63. Slate, hard and black ,
64. Quartz vein 1
65. Slate, hard, black, and carbonaceous 3 6
66. Coal, full of quartz impurities 2
67. Slate . 1 0
68. Sandstone, fine grained and hard 2 1
69. Quartz vein : . . 1
70. Sandstone, fine grained 4 0
71. Sandstone, fine grained 2 1
72. Shale, hard, passing into a hard fine-grained sandstone 10 1
73. Shale, carbonaceous 2 2
74. Shale, arenaceous, passing into a fine sandstone 3 0
75. Sandstone, fine grained 2 0
76. Shale, carbonaceous 4 9
77. Shale, fine grained 1 2
78. Shale, sandy 3 7
79. Sandstone, gray, hard, and fine 3 9
80. Shale, black, fine grained 2
81. Shale, arenaceous, with bands of graphite 3 7
82. Shale, black 1 8
83. Sandstone, fine grained 2 3
84. Shale, black, with quartz 2
85. Sandstone, with quartz veins 3 3
86. Sandstone 6 0
324 GEOLOGY OF THE NAERAGANSETT BASIN.
87. Graphite, impure 1 6
88. Sandstone 2 10
89. Shale, black and highly carbonaceous 1 C
90. Coal li
91. Sandstone 3 9
92. Quartz vein 3
93. Sandstone 1 4
94. Quartz vein 1
95. Sandstone, gray 3 9
96. Slate, drab arid hard 2 3
97. Slate, same as above 3 2
98. Sandstone 8
99. Shale, carbonaceous 1 0
100. Sandstone, fine grained 1 4
101. Shale, carbonaceous 4
102. Sandstone, gray 10
103. Sandstone, dark gray '... 3
104. Sandstone, lighter gray 5 0
105. Sandstone, dark gray 1 4
106. Shale, carbonaceous 9 8
107. 3 1
108. Sandstone, fine, filled with carbonaceous matter 1 6
109. Sandstone 1 8
110. Sandstoue, coarser than above 1 3
111. Sandstone, with thin seams of carbonaceous matter 4 0
112. Shale, black and carbonaceous, dip 43° 1 9
113. Sandstone, dark gray 4
114. Shale, arenaceous, filled with carbonaceous matter 2 0
115. Slate, black 1 8
116. Sandstoue, like that at 120 feet down 8
117. Shale, carbonaceous 1 10
118. Shale, arenaceous, with carbonaceous matter 1 2
119. Sandstone 4
120. Shale, arenaceous, with thin seams of carbonaceous matter 6 4
121. Shale, highly carbonaceous 2 0
122. Sandstone, hard and fine grained 1 0
123. Argillite - 4 9
124. Sandstone 1 0
125. Argillite 10
126. Sandstone, hard and tine, with small calcite veins 1 3
127. Argillite, carbonaceous 2 0
128. Shale, arenaceous, containing, from one-eighth to one-fourth inch apart,
very thin layers of granite 3 0
129. Sandstone, gray 3 3
130. Coal, filled with quartz, iron pyrite, and chlorite 1
EBCOED OF BOEma IN POETSMOUTH. 325
Feet. Inches.
131. Argillite 1 5
132. Saudstoue, with calcite veins and iron pyrite 1 0
133. Shale, carbonaceous 4 n
134. Sandstone, tine to coarse grained, with calcite veins 3 9
135. Sandstone, hard and darker than above 1 lo
136. Sandstone, like above, with carbonaceous matter 3 5
137. Sandstone, fine grained, gray, entirely free from carbonaceous matter. . G
138. Shale, carbonaceous 22 C
139. Sandstone, fine grained 1 (i
140. Shale, carbonaceous y
141. Sandstone, fine grained 1
142. Slate, hard, black, becoming carbonaceous toward end, dip 28° at top. . 4 0
143. Sandstone, bard, flue grained 1 1
144. Goal, broken and filled with calcite covered with iron ijyrite, dip 63°. . 5
145. Sandstone, fine grained 3 2
146. Shale, carbonaceous 1 0
147. Sandstone, fine grained and indurated 10
148. Coal, brecciated and filled with calcite 2
149. Shale, hard black 6
150. Argillite 8 4
151. Shale, black, becoming carbonaceous toward middle and arenaceous at
the bottom 7 4
152. Coal (carbonaceous breccia) 3
153. Sandstone 9
154. Sandstone, with small veins of calcite 1 0
155. Shale, carbonaceous 1
156. Shale, arenaceous 1 0
157. Shale, highly carbonaceous, dip 36° 2
158. Sandstone 1 3
159. Sandstone, gray 1 3
160. Argillite 3 8
161. Shale, carbonaceous - 1 4
162. Shale, hard, fine, and arenaceous 2 6
163. Shale, arenaceous 11
164. Shale, arenaceous and carbonaceous between 440 and 442 feet down 22 1
165. Shale, carbonaceous 4 5
166. Coal, with veins of quartz near bottom 6 5
167. Sandstone, gray 1 0
168. Shale, carbonaceous 3 1
169. Sandstone, gray 3 10
170. Sandstone, dark gray and fine grained 2 3
To bottom of hole, 475 feet 11 inches, reached February 23, 1887, at 5.30 p. m.
326 GEOLOGY OF THE NAEEAGANSETT BASIN.
LINE OF EXPOSURES THREE-EIGHTHS OF A MILE WEST OF THE NEWPORT
ROAD.
Almost half a mile north of Lawtons Valley a much smaller stream
gully is seen extending down the hillside. On the south side, near the
railroad, carbonaceous black shale containing occasional fern-leaf impres-
sions is exposed. The dip is apparently very low eastward. Farther up,
the shale turns to bluish black. At the brow of the hill, south of the gtilly,
there occurs a small conglomeratic layer. Toward the top of the gully
sandy layers come in.
The creek entering the marshy pond south of Coggeshall Pond also
shows dark blue-black shales, with interbedded sandy layers, in the banks
south of the valley and near the railroad. The dip is at first 40° E.,
but becomes steeper eastward. The same series continues to be exposed
farther up along the valley, the strike at one point being N. 30° E., dip
very steep east. The rock contains sandy layers and in places also becomes
very carbonaceous. At the brow of the hill north of the creek a coarse,
thick, whitish sandstone layer shows a strike of N. 30° E., the dip appar-
ently 60° E. Southward this sandstone terminates siiddenly, but north-
ward it continues for a long distance. To the eastward the shale series
overlies this sandstone again. The sandstone contains in places a few small
pebbles. It forms only a layer in the shale series.
The coarse sandstone is exposed again three-eighths of a mile east of
north of the creek. Here again a few pebbles occur. Strike N. 12° E.,
dip E. Northeast of this locality the same coarse sandstone is overlain by
carbonaceous shale; strike N. 20° E., dip 40° to 45° E. Southeastward,
halfway between the last two exposures and the Newport road, bluish-dark
shale is exposed at several localities, evidently overlying the coarse sand-
stone, and apparently dipping steep to the east. Northwest of the last
sandstone outcrop dark-bluish shale is exposed. It belongs beneath the
sandstone bed, but contains itself more sandy layers, and the dip is
eastward, although apparently only 20°. The last exposure extends as
far as an east-west road running to the beach. A quarter of a mile
northward a projection at the northwestern angle of the hill shows a more
greenish shale; strike N. 16° E., dip 60° E. Another exposure of the
shale occurs a quarter of a mile northward, south of the brook. The shale,
BUTTS HILL. 327
more bluish in color, is seen again north of the brook, along the south side
of an east- west road; strike N. 20° E., dip very steep eastward. In the fields
north of this road the shale continues to be exposed, and just before reach-
ing the road which crosses the 140-foot hill (see map, PI. XXXI) southwest
of a house the bluish shale is exposed, and contains a more sandy layer
just south of the building; dip not certain, strike apparently N. 35° E.
SHALE SERIES AT BUTTS HILL.
Three-quarters of a mile northeast of Butts Hill, along the eastern
Newport road, cai'bonaceous shale with fern leaves and other plant remains
occurs. Strike N. 6° E., curving to N. 20° W at the north end of the
exposure; dip 15° to 20° W. Northeast of Butts Hill, along the same
I'oad, just noi'th of Chas C. Hazard's house, a coal mine was formerly worked.
The strike of the beds is N. 15° E., dip 15° to 20° W. The structure of
the northern third of Aquidneck Island is evidently that of a syncline.
All around the top of Butts Hill, especially in the neighborhood of
the old fort, the bluish-black and coaly shale is frequently exposed. North
of the old fort and just south of the road crossing the hill is an old quarry.
Near the top of this exposure the blackish shale contains fern-leaf impres-
sions. The dip of the shale is low, 5° to 10° S. In places there is evidence
of much crumpling here by a force acting east and west, and the result is a
series of narrow folds trending north-south and giving rise to variable east-
west dips, generally to the westward along the east side of the hill. Butts
Hill evidently lies in the trough of the syncline.
GREEN SHALES AND CONGLOMERATES OF THE NORTHERN SYNCLINE.
GREEN SHALES ALONG THE WESTERN NE\A?PORT ROAD.
Half a mile north of the point where the Newport road crosses Lawton
Valley greenish-blue and bluish shales occur along the road and imme-
diately westward. The strike is about N. 10° E., dip probably 20° E. A
mile northward, on the east side of the road, greenish-blue slate and sand-
stone strikes N.-S., dip 20° to 40° E., as well as could be determined. A
quarter of a mile northward, at an angle of the road, more greenish shale
occurs. Three-eighths of a mile northward the green shale is seen exposed,
east of the road corners, on the south side of the road. Green shales occur
328 GEOLOGY OF THE NARKAGANSETT BASIN.
also oil tne southwest and northeast sides of the hill immediately northward,
and again, for the last time, a quarter of a mile northward, west of the road.
The green shales therefore form a series overlying the bluish-black
shales, although evidently a part of the same and representing only the
upper courses of the series.
PORTSMOUTH CONGLOMERATES.
A road leads from Portsmouth Grove Station eastward to the Newport
road. An eightli of a mile southeast of the road corners conglomerate
with quartzitic pebbles up to 10 inches in diameter is found. The trend of
the exposures is about N. 10° to 15° E., but the strike and dip could
not be satisfactorily determined. Northward, the same distance northeast
of the road corners, bluish sandstone, varying to green, in places coarse,
and with some layers of fine conglomerate, is seen. The trend of the
exposures is N. 12° E. A quarter of a mile northeast of the crossroads
the greenish slate is seen on the hillside nearer the Newport road, becom-
ing moi'B bluish eastward and merging into a more sandy rock toward the
northeast, where it is more nearly in line with the pre\nous exposure.
Three-quarters of a mile from the crossroads, along the top of the hill,
considerable sandstone occurs. It includes a narrow greenish shale layer,
and at the southwest end a few thin conglomeratic beds, with pebbles not
exceeding half an inch in diameter. An eighth of a mile northeastward,
and the same distance from the next east-west road, greenish-blQC shale
again occurs westward, with gray sandstone eastward. A few layers
are coarse, almost conglomeratic. North of the east-west road loose
pebbles, similar to those usually found in conglomerates, occur with con-
siderable frequency on the east side of the hill, east of the regular green
shale exposures of the hill. Over three-fourths of a mile northward, an
eighth of a mile northeast of the crossroads, begins a ridge extending
N. 80° E., across the next road leading northward. This ridge is formed in
the main of conglomerate, composed of quartzitic pebbles often 8 inches
or longer in diameter, and containing fossil oboli. The conglomerate
strikes N. 20° E.; the dips are difficult to determine, but seem to be in some
places nearly vertical, in others less steep. A greenish-blue shale bed is
apparently interbedded in places. This ridge of conglomerate lies half a
mile a little west of south of Butts Hill, and, like the shales of that hill, is
POSITION OF SLATE HTLL SHALES. 329
believed to occupy the axis of the synchne. If that be true, the following
exposures may be of interest, since they lie east of the sandstones and
conglomerates which are nearer the western Newport road.
A number of exposures of coarse quartzitic conglomerate lie a
quarter of a mile directly south of the ridge, and south of an east-west
road. Their strike seems to be north-south.
Three-quarters of a mile southward, in the Portsmouth camp-meeting
grounds, coarse conglomerate is exposed, interbedded with sandstone. Stiike
N. 7° W., dip 70° W. This exposure seems to lie on the eastern side of the
syncline.
Southward no inore coarse conglomerate is exposed. The next exposure
lies a mile southward, south of the next east-west road, on the west side
of the hill. Near the base of the hill occurs bluish-green sandstone with
narrow streaks of pebble layers, the pebbles being of very small size.
Farther east bluish-green shale is exposed at several points. This shale
resembles the greenish shales described as occurring beneath the sandstones
and conglomerates on the west side of the syncline. Their occurrence in
the same position on the east side is significant. Strike north-south, dip low
westward.
RELATIONS TO SLATE HILL SHALES.
It will be seen that the structure of the northern tliird of Aquidneck
Island is that of a syncline, the great mass of the rocks being dark carbona-
ceous shales, and to a less degree sandstones. Overlying these, near the
top, is a thin series of greenish shales, and a remnant of a conglomerate
series overlying the green shales is still preserved in places near the
middle of the syncline. A little over two miles south of the green shales
above described, from the east and west sides of the syncline, the green
shales of Slate Hill begin. The synclinal structure is no longer apparent
so far southward. Instead of the single syncline of the northern third of
Aquidneck the soLithern third shows at least three synclines — one east along
the Sakonnet shore; a second, the southward-plunging syncline in the
Paradise Rock series and west of Eastous Point; a third, just west of
Miantonomy Hill and in the Coasters Harbor Island region.
Possibly the green shales near the top of Slate Hill represent the
place where the marked southward pitch of these more southern synclines
330 GEOLOGY OF THE NARRAGAlSrSETT BASIN.
begins. It is in the latitude of the Slate Hill sections, and thence east-
ward and westward to the shore on either side of Aquidneck Island, that it
is most difficult to secure evidence of marked strikes and dips, a character
often attending shaly rocks not steeply inclined, since the cleavage then
most readily obscures the stratification, not departing far from its plane.
CHAPTER VII.
THE KINGSTOWN SERIES.
Unity and lithological character of the Kingstown sandstone series. At tllG preSOllt StagB
of investigation it does not seem feasible to separate the Carboniferous
strata lying along the western border of Narragansett Bay, between East
Greenwich and Narragansett Pier, into divisions of geological value. No
fossils have so far been discovered in them. Lithologically they consist of
frequent alternations of the following rocks:
First. A coarse quartzitic sandstone, almost an arkose, evidently derived
in large part from some earlier granite area. This sandstone frequently
contains flakes of white mica, or of biotite and some other dark mineral.
The color of the sandstone in general is white, the quartzitic elements very
much predominating.
Second. As this sandstone becomes coarser it contains, at first, scattered
quartzite pebbles, and then thin layers of a conglomeratic nature, merging
into triie conglomerates a few feet in thickness, the pebbles of which usually
consist of quartzite, occasionally of granite, and, except in a few localities,
do not exceed an inch or one inch and a half in diameter.
Third. As this sandstone becomes finer it also turns darker, the varia-
tion in color being usually due to an increase in the amount of carbonaceous
material. In some of the more northern localities, however, the coarser and
medium-grained sandstones are of a bluish color, which appears to be due
to a decrease in the quantity of carbonaceous matter, making more evident
the dissemination of iron in some form throughout the rock. The blue
color is usually, in the case of the less carbonaceous sandstones, a sign of
less metamorphism. During metamorphism the feiTuginous matter seems to
have collected partly in the form of magnetite and partly as a constituent of
black mica, leaving- the general mass of the rock whitish, but flecked with
black specks.
Fourth. The medium-grained sandstones merge into a very fine-grained
331
332 GEOLOGY OF THE KARRAGANSETT BASIif.
and always very dark or black rock, the color being due to its carbon-
aceous character. It is difficult to determine whether to call this rock a
fine-grained sandstone or a gritty shale, since it is sometimes massive and
without cleavage and sometimes shaly.
Fifth. This merges into shale, the structure being due to cleavage.
The micaceous elements of the sandstones here become yerj abundant-
Sericite is a common constituent; the color at a distance often appears rather
dark, almost black, especially where moistened by water; but at closer range
it usually shows a dark-blue color, the dark tint being evidently due to the
presence of ferruginous and carbonaceous matter.
Sixth. Occasionally the dark-blue shale becomes black, contains much
carbonaceous matter, and is comparable with the coaly shales of the less
metamorphosed part of the basin.
The types of rocks described above alternate in an irregular manner,
making it imjDOSsible at the present to treat of them otherwise than as a
geological unit. From Hazzard's quarry, a mile north of Sauuderstown, to
the angle of the shore a third of a mile south of Watsons Pier, the expo-
sures are almost continuous. Here it is seen that the shales are an important
part of the Carboniferous section on the western side of the bay, forming
from a third to a half of the total thickness of the rocks exposed. The fine-
grained sandstones are another important element. The coarse sandstones,
although a conspicuous feature farther inland, can here hardly form a fourth
of the total section.
Away from the coast, westward and northward, the exposures consist
chiefly of sandstone, often coarse and conglomeratic. Finer sandstones also
occur, but shales are rather infrequent, excepting in the regions (1) imme-
diately south of Wickford. (2) a mile south of Sandy Point, on Potowomut
Neck, and (3) a mile and a half directly south of tlie second locality.
This diminution in the relative amount of shale exposed toward the west
is striking, and would appear to indicate a corresponding lithological
distinction between the shore exposures and the more inland part of the
Carboniferous series toward the west and north were it not for the pi'ob-
ability that the more isolated iidand exposures represent chiefly the
harder, less eroded, and therefore at present more elevated beds of the
Carboniferous series, while the softer and less enduring rocks, including
the finer sandstones and especially the shales, exist in considerable thickness
KINGSTOWN^ SERIES AT THE BONNET. 333
in any fully exposed section, but suffered more from weathering and now
lie hidden nnder the more recent glacial and sand-plain deposits, leaving
the coarser sandstones to form almost the only exposures rising above the
sand-plain level. For this reason it is not safe to make any distinction
between a more shaly and a less shaly series on the western shore of the
bay. On the contrary, it is very likely that shales also form an important
element of the series northward and westward, away from the shore line,
but that, on accoimt of their more ready erosion, they do not frequently
appear above the soil.
On account of the far greater abundance of sandstones among the
rocks of this western area, so typically developed in South and North
Kingstown, than in the Aquidneck shales farther east, the name Kingstown
sandstones is suggested for this western complex of strata, as being of value
in designating them when it is desirable to distinguish the two formations
where they are typically develoned. The Kingstown sandstones underlie
the Aqiiidneck shales.
Section from the Bonnet to Boston Neck. At the Bomiet tllC KlugStOWU SerieS dipS
about 60° E., giving an exposed thickness of about 700 feet, with a possible
thickness of about 1,350 feet, if we include the area as far west as Wesquage
Pond, which area, although without exposures, may be presumed to be under-
lain by similar rocks. Judging by the strikes along the shore, the lowest
part of this section, consisting of the strata supposed to underlie the eastern
edge of Wesquage Pond, can lie only a short distance above the most
eastern exposures on Boston Neck and at the South Ferry. The most eastern
exposures on Boston Neck dip nearly vertically; southeast of Watsons
Pier the rocks dip 60° E.; west of the pier they dip 45° E.; three-quarters
of a mile northward, 15° E.; these exposures, with the intermediate terri-
tory, add approximately 800 feet to the section already given, and make
a total of 2,150 feet for the thickness of the Carboniferous section from the
Bonnet southward, assuming that no folding has taken place.
Section from the Bonnet to Hazzard's quarry and Indian Corner. TllC Strata CXpOScd aloUg
the shore of Boston Neck are probably repeated north of South Ferry,
but the dips here are low, between 20° and 40° E., at times nearly hori-
zontal, so that until much more accurate field work is done the strata north
and south of the Bonnet can not be strictly compared with one another.
The Bonnet section as far west as Wesquage Pond was estimated at 1,350
334 GEOLOGY OF THE NAEEAGANSETT BASIN.
feet. The sections from South Feny to the exposures nearest Saunders-
town can, on account of these low dips, be estimated at about 350 feet,
making a thickness of 1,700 feet from the eastern part of the Bonnet to
Saunderstown. As the strata along- the shore approach Saunderstown from
the south, the dip along the strike increases, until north of Saunderstown it
becomes nearly vertical. Then the di]3S, continuing along the strike, become
35° and 45° E., but in the section across Hazzard's quarry (PL XXI) and
westward to the top of Barbers Height the prevailing dip varies between 50°
and 65° E., adding about 2,200 feet to the 1,700 feet already accounted for,
making a total of 3,900 feet for the section between the eastern part of the
Bonnet and Barbers Height. To this must be added at least 1,600 feet
more, in order to include the exposures south of the road nearly half a
mile west from the top of Barbers Height, making a total section of 5,500
feet for the thickness of the Carboniferous from the Bonnet to the locality
just mentioned. Making allowance for the change in the strike of the rocks
toward the west of north, on going northward, a thickness of at least 3,600
feet must be added, in order to include both the exposures at Indian
Corner and those at the locality half a mile south of the corner, east of
the road, so that an estimate of 9,100 feet for that part of the Saunderstown
sandstone series exposed on the western shore of the bay would be A^ery
moderate if the strikes and dips of the scattered exposures were considered
as fairly representing the general structure of the strata beneath the soil.
This estimate seems excessive, and a series of close synclines and anticlines,
or of faults, may be imagined in order to reduce it to more moderate dimen-
sions. It should, however, be remembered that at present no facts are
known in this part of the field warranting such an interpretation of the
structures actually observed. For a continuation of the discussion of the
thickness of the Kingstown series in the southwestern part of the Narra-
gansett Bay area, see page 336.
Kingstown series in southwestern Cranston and western Warwick. At tlie preSeut Stage of
inquiry it does not appear safe to make many statements as regards the
equivalency of the Kingstown group north of East Greenwich to rocks
exposed in the southern part of the field. The coarse conglomeratic
sandstone at Hills Grove may belong to the Saunderstown series. The
mediiim-grained sandstone east of Hills Grove and southwest of Norwood,
with its bluish-gray color, is very similar to some of the sandstones exposed
KINGSTOWN SERIES IN CEANSTON AND WARWICK. 335
along the road 1 and 2 miles north of Wickford. If the escarpment
west of the railroad from Wickford Junction to East Greenwich, Coweset,
Apponaug, Natick, and northward, marks the western boundary of the
Carboniferous basin, south as well as north of East Grreenwich, the
equivalents of the Saunderstown sandstones must lie immediately east of
that escarpment in Cranston and Warwick, and would be expected to show
a considerable thickness and some lithological resemblance to the exposures
southward. As a matter of fact, however, the exposures in Warwick are
altogether insufl&cient to afford the basis for a judgment on this point. In
southwestern Cranston, north of Natick and Pontiac, sandstones occur
dipping at a low angle to the eastward, except along the Carboniferous
margin. Beginning, however, near the State almshouse and extending
thence northward along the east side of the hill occupied in part by the
Reform School is a series of black shales, becoming in places very coaly.
These coaly shales are the conspicuous feature of the Carboniferous section
in western Cranston, and appear in the mines east of the Sockanosset
Reservoir and on the east side of Rocky Hill. Beneath the coal-bearing
shales at Sockanosset Hill are others of dark-blue or black color, often
ottrelitic, which are exposed in the vicinity of Sockanosset Reservoir and
near Waylaud Station. Associated with these shales are sandstones, but
these more northern sandstones are usually bluish gray, or more or less
carbonaceous and medium grained, and, although not very different from
the sandstones farther southward, do not closely resemble them
While, therefore, it seems beyond qiiestion that the rocks of western
Warwick and Cranston form the northern extension of the Kingstown series,
they present somewhat different lithological features, the shales being much
more coaly, and at one horizon containing workable coal; moreover, the
sandstones are finer grained and apparently less quartzitic and less suggestive
of arkose. Still, while the more carbonaceous character of the shale north-
ward is recognized, the abundance of dark-blue shales, certainly containing
carbonaceous material, along the shore southward from Barbers Height
to the Bonnet should not be forgotten. The more northern exposures, in
Cranston, will therefore be regarded as simply a more carbonaceous phase
of the Saunderstown series, while they evidently correspond also to the
lowest part of the lower part of the Tenmile River beds or the Pawtucket
shales of Mr. Woodworth.
336 GEOLOGY OF THE NAERAGAlSrSETT BASIN.
Probable thickness of the Kingstown sandstone series in Cranston and Warwick. 1 lie clipS OI tllG
rocks exposed in southwestern Cranston are rather low, usually varying
from nearly horizontal to 25° NE. and E. The miners report a steeper dip
in the mine on the east side of Sockanosset Hill, the reported inclination
being about 50° E.; but this, judging from surface exposures, seems to be
but a local increase of dip.
On the eastern side of Warwick Neck, toward Rocky Point, the
sandstones forming the slopes of the hill dip about 45° E. The first
sandstones and shales met on the road to Rocky Point, and some of the
sandstone and conglomerate exposures at the point also, slope about 20° E.
Between Hills Grove and Norwood Station and Warwick Neck there are
no exposures. Under these circumstances it is not safe to make calcula-
tions as to total thickness of the series of strata underlying Warwick and
Cranston; but with an average inclination of 20° E., which is hardly war-
ranted, considering the often lower dips where the rocks are actually
exposed, the total thickness of the Carboniferous series from southwestern
Cranston to the conglomerates of Rocky Point would be about 11,200
feet. The actual exposures suggest that this estimated thickness is perhaps
extravagant. (See pp. 334, 337.)
If a series of close synclines and anticlines be imagined along the
western margin of the southern part of the bay, extending northward into
Warwick and Cranston, the preceding estimate can hardly be said to have
any value whatever. In that portion of the field investigated by the writer,
limited to the Narragansett Bay quadrangle, there is no actual field evidence
of such folding, either north or south, although the great east-west extension
of the Kingstown area of exposure is suggestive of such folding.
Warwick Neck exposures. — The lowest part of tlus thickuess of 11,200 feet of
Carboniferous strata in Warwick and Cranston is equivalent to the Kings-
town series as exposed farther southward. Whether the Warwick Neck
exposures belong to the Kingstown series can not be determined by the
evidence secured in the area in question. Near the southern end of Warwick
Neck carbonaceous shales occur along the shore, the contortion suggesting
local folding. Black shales are found in the railway cut at the lower end of
the neck Heavy sandstone beds, some medium conglomerate layers, and
dark-blue shales are seen on the eastern side of the neck, with more bluish
shale on the east before reaching the conglomerate series of Rocky Point.
KINGSTOWIJr SERIES EAST OF THE BONNET. 337
Lithologically the Warwick Neck exposures could be readily associated
with the northern extension of the Kingstown series as exposed in south-
western Cranston, and might therefore be considered as forming part of the
same series. They would constitute in that case the upper portion of the
Kingstown series in the northwestern part of the Narragansett Bay area.
This would make the Warwick Neck and Rocky Point exposures roughly
equivalent to the more eastern exposures mentioned in the following
paragraphs.
Exposures on the western islands of the bay. Tlie KiugStOWU SerieS appCarS tO be
not hmited to the western shores of the bay. The strata exposed on (1)
Dutch Island, at (2) Beaver Head on Conanicut Island, toward the south
of Dutch Island, (3) north of Round Swamp on the northern half of the
island, (4) on Hope Island, and (5) along the western shore of Prudence
Island, north of the wharves, all seem to belong to this series.
Thickness of strata between the Bonnet and Dutch Island. The UCarCSt poiut of apprOacll
of the island exposures with those on the west shore is between Dutch
Island and Saunderstown, where they are distant 4,200 feet. Beaver Head
is about 5,400 feet from Sonth Ferry, and the most western part of northern
Conanicut is 6,000 feet distant from the Hazzard quarry region north of
Saunderstown. While, therefore, it may appear rash to associate in one geo-
logical series strata so far disconnected, other facts make this relation more
than probable. Tracing the rocks of the Bonnet section northward on the
map, in accordance with the suggestions offered by the actual strikes of the
rocks exposed along the shore, it will be seen that the northward extension of
the Bonnet series must lie a considerable distance toward the east of Saun-
derstown, while the southern extension of the Dutch Island strata would
approach the western shore at the Bonnet. Traced in this way the Bonnet
section is found to approach the Dutch Island section within 1,350 to 1,750
feet. Assuming a dip of 60° for this unexposed part of the section, the
Bonnet section underlies the Dutch Island section from 1,200 to 1,500 feet.
The dips, however, on the Saunderstown shore opposite the island do not
exceed 40°, while the western shore dips of Dutch Island are also usually
less than 50°, so that the two sections may possibly approach each other
within 975 to 1,200 feet. Considering this moderate interval of unknown
strata, and the absence of any signs to the contrary, the lithological simi-
MON xxxiii ii2
338 GEOLOGY OF THE NAERAGANSETT BASIK
larity of the Dutch Island rocks and the Kingstown sandstone series may
be regarded as conclusive of their close geological relationship.
The Dutch Island exposures must therefoi'e be added to the sections
exposed on the mainland in order to form an estimate of the total thickness
of th Kingstown series in the southwestern part of the Narragansett Bay
region. This is discussed more fully in the third paragraph following.
Lithoiogy of the Dutch Island series. — lu general, tlic Strata of Dutch Island may
be described as consisting chiefly of sandstones with subsidiary conglom-
erate layers, underlain on the western side of the island by a series in
which black, often very cai'bonaceous, shales predominate. Considering
the black color of some of the Bonnet shales, the Carbonaceous character
of the fern-bearing shales on Dutch Island is not unexpected. The con-
glomerate layers evidently contain larger pebbles than most of the conglom-
erates found high up in the series on the western side of the bay, but it is
evident that their length is largely due to stretching. The pebbles are also
less qnartzitic than lower down. But it is the considerable abundance of
sandstones in the Dutch Island section that suggests relationship with the
Kingstown series.
Beaver Head section. — At Beavcr Head, couglomeratc is exposed only on the
western border of the hill, near low-water mark. The main mass of the
hill is evidently composed of black shales, with intercalated subsidiary
thin sandstone beds and some arkose. The shales are decidedly carbona-
ceous. The Beaver Head section is evidently an introduction to the Aquid-
neck shale series as exposed farther eastward on the island, and seems to
have its likeness in the carbonaceous shales at the base of the shale series
on the western side of Prudence Island.
Total thickness of the Kingstown series, including the conglomerate at Beaver Head. Taking 40*^
as an average of the eastward dips on Dutch Island, the thickness of the
Dutch Island section is about 1,050 feet; this, added to the unknown inter-
val of 975 to 1,200 feet occupied by the western passage (see bottom of pre-
ceding page) and the estimated thickness of 9,100 feet for the series as
exposed on the western shores of the bay from the Bonnet to Hazzard's
quarry, Indian Corner, and southward (see pp. 333 and 334), would give
a thickness of from 11,125 to 11,350 feet for the whole series of Kingstown
sandstones, including Dutch Island. An additional thickness of 225 feet
would probably include the conglomerate layers exposed at low tide on the
western margin of Beaver Head, so that 11,500 feet would express, in round
KINGSTOWN SERIES OF NORTHERN CONANICUT. 339
numbers, the total thickness of the Kingstown series in the southwestern
part of the Narragansett Bay area. It will be remembered that in the
northwestern part of this area, in Warwick and Cranston, the estimated
thickness was 11,200 feet (see p. 336).
Western shore of conanicut. — The rocks along the wcstem shore of Conanicut
also bear considerable resemblance to the Kingstown series as exposed on
the mainland, owing to the presence of abundant sandstones, but they are
still more similar to the strata exposed on Dutch Island, of which they are
probably the continuation. Along the shore opposite Slocum and Great
ledges there is considerable coaly shale, some of which, according to T. N.
Dale,^ contains fern impressions. There is also, an abundance of sandstone,
interbedded with which are subsidiary conglomerate layers with very much
elongated pebbles, bearing considerable resemblance lithologically to the
conglomerate of Dutch Island and the layer on the western margin of
Beaver Head. The strikes along these ledges practically follow the shore.
From Sand Point northward similar coaly shales and sandstones with
subsidiary conglomerate layers are exposed. The strike is nearly N. 3° E.
Along the entire Avestern shore the dips are eastward, usually, however,
quite low.
Eastern shore of Conanicut. — Wliilc tlic cxposures aloug thewestcm shore of
northern Conaniciit can be safely correlated with the strata on Dutch Island
and western Beaver Head, the position and geological structure of the strata
forming the middle and eastern parts of Conanicut remain, to say the least,
problematical. East of North Point occur coaly shales, apparently showing
lateral squeezing from east to west. Along the eastern shore are found
coaly shales, at one point with fern impressions; also gray sandstones. The
strikes average N. 10° E., and the dip is usually very steep, nearly vertical,
but shows in places sudden variations which can most readily be reconciled
with crumpling. The cleavage often obsciires the bedding. The absence
of conglomerate layers along the eastern shore is a conspicuous feature in
contrast with the more western line of exposures, including western
Conanicut, Dutch Island, and Beaver Head. The exposures along the east-
ern shore of noi-thern Conanicut may therefore belong to another horizon,
possibly a higher one corresponding to the strata overlying the conglom-
erates on the western margin of both Beaver Head and Prudence Island.
' On metamorphism iu the Rhode Island coal basin : Proc. Newport Nat. Hist. Soc, Doc. 3, 1885,
pp. 85-66.
340 GEOLOGY OF THE NAREAGANSETT BASIN.
Probablefoldingin the northern part of Conanicut Island. Tlie clifficultieS of tllG pi'Oblem
may be briefly stated as follows: The green sliales of the southern half of
Conanicut make their first appearance at the southern end of the lagoon
east of Beaver Head. From this point they extend in a direction N 37° E.
to the eastern shore of the island, being last seen at a point a mile north of
Freebodys Hill. The highest layer of conglomerate at Beaver Head occurs
a little above low-water mark on the extreme western shore of the head-
land. The next most eastern exposure of conglomerate northward lies
along the most western part of the shore of Conanicut, northwest of Round
Swamp. The second locality lies about N. 10° E. from the first. The
average strike of the sandstones, coaly shales, and conglomerate beds on
the western side of northern Conanicut is not more than N. 10° E., which
seems to suggest a connection between the Beaver Head conglomerate and
the conglomerates farther northward. In that '"ase, however, there is a
divergence of about 27° between the conglomerate layers on the west and
the green shales on the east, which suggests a thickening of the intervening
strata northward, an unconformity, a peculiar form of fan-shaped folding,
or a fault. There is, however, no good geological evidence for any one of
these suggestions.
Curiously enough, the strikes on the eastern side of Conanicut, north
of the latitude of southern Gould Island, are also N. 10° E. This makes it
difficult to imagine the precise nature of a system of folding which would
give such an increase of area in an east-west direction northward as
has been just described, and which nevertheless could escape detection in
the regions where actual exposures occur. The strata on the western shore
of northern Conanicut dip eastward at a low angle. On the eastern shore,
north of the latitude of southern Gould, Island, the dips appear very varia-
ble, being sometimes almost vertical. These steep dips may be an expres-
sion of that folding which must also obtain over the middle length of the
island, in order to reconcile the apparent divergence of the conglomerate
layers and the green shales as described above, without recognizing a
marked increase in the thickness of the strata involved or any possibility of
faulting or of an unconformity. The facts observed elsewhere in the field
do not warrant the assumption of a great unconformity here, but the possi-
bility of faulting must not be precluded.
If the possibility of a faiilt starting somewhere northeast of Beaver
KINGSTOWN SERIES ON HOPE ISLAND. 341
Head and increasing toward Round Swamp and beyond be excluded, a
low general eastward dip of a series of strata, subjected to abundant sub-
sidiary folding, pitching southeastward along their southern border, is the
only explanation that occurs to the writer, and very much more field work
is necessary to form anything like a safe opinion on this point. In the
absence of more accurate information an estimate of the maximum thick-
ness of the strata involved in the northern Conanicut complex seems unwar-
ranted. The thickness certainly amounts to as much as 1,735 feet, but it
may many times exceed this.
Hope Island. — Llthologically the rocks forming Hope Island resemble the
strata exposed on the western shore of the bay more closely than the more
northern exposures along the western side of northern Conanicut. This
may be due in part to the greater metamorphism of the Hope Island rocks.
The sandstone here is often quartzitic, of white color, and contains
biotitic mica. The interbedded fine-grained sandstones are usually very
black. Black shales are found only along the western and northern sides
of the island, and form evidently the lower beds of the small section here
involved. The quartzitic sandstones contain scattered pebbles and thin
conglomeratic layers. Conglomerates are present to a certain degree in
all the sandstone layers. On the western side of the island they are a minor
feature, while on the eastern side they form half the rock. The pebbles
are uniformly small, usually not over IJ inches in diameter. Many of
them are decidedly quartzitic or granitic. There has been little flattening
of the pebbles by shearing. The strike over the southern three-fourths of
the island averages N. 30° E., with an easterly dip of 60° to 80° on the
western side, and a dip of 30° to 45° E. on the eastern shore. These
strikes also suggest that the Hope Island section may underlie the exposures
on the western shore of northern Conanicut, notwithstanding the northerly
strikes of the latter. The section exposed on the island is estimated to have
a thickness of at least 800 feet.
At the northern end of Hope Island the dip of the strata is very low
to the northeastward. Were it not for this fact the more southern strikes
would carry these strata approximately toward Pine Hill and Gull points,
on northern Prudence Island. The outlines of the coast and the trends of
the main hills on northern Prudence Island and on Patience Island suggest
342 GEOLOGY OF THE NAEEAGA^J^SETT BASIN.
a strike toward the west of north for the underlying strata, which would
agree with the exposures at Rocky Point.
Kingstown series exposures on the western islands. FrOUl tllO BoUUet tllC KingStOWU
series has been traced iiorthward into western Warwick and southwestern
Cranston. The relationship of the overlying Dutch Island section has been
shown, and similar rocks have been traced along, the Avestern part of north-
ern Conanicut, and others form Hope Island. The exposures at Beaver
Head and along the eastern shore of northern Conanicut appear to be a
more coaly variation, intermediate between the sandstone series beneath and
the green and dark-blue shales above.
Prudence Island. — Litliologically somewliat similar features are presented
along the western side of Prudence Island, where sandstones and some con-
glomerate occur along the shore north of Prudence Park wharf, dipping-
eastward, on the average, about 25°. Overlying these are black carbona-
ceous shales and sandstones containing fern leaves. Higher, near the
wharf, are shown the dark-blue shales. If the dark-blue shales be corre-
lated with the green and dark-blue shales of Conanicut, and if the sand-
stones and conglomerates be associated with the Kingstown series as
shown on Dutch Island, then the coaly shales are equivalent to the black
shales forming the main mass of Beaver Head. Comparisons at so great
distances have, of course, little value. The real reason for considering the
sandstones and conglomerates of the western shore of Prudence Island as
equivalent to the top of the Saunderstown series is their situation beneath
a considerable thickness of shales. The thickness and lithological charac-
teristics of these shales seem to warrant their correlation with the great
body of shales on Aquidneck Island and the southern part of Conanicut
Island, the whole forming a geological group in the bay region of the Nar-
ragansett Basin, winch group is here called the Aquidneck series, and
which overlies the Kingstown series. The unity of the shale series will be
discussed further on. Correlating the conglomerates on the western shore
of Prudence Island with the conglomerate at Beaver Head, it may be sug-
gested that the sections at Rocky Point may not far underlie their horizon.
The actual exposure of sandstones and conglomerates north of the
wharf at Prudence Park can hardly exceed 50 feet. The overlying coaly
shales may possibly amoimt to 150 feet in thickness south of Prudence
Park wharf, but if that is the case they certainly thin out rapidly north-
KINGSTOWN SERIES OP WESTERN BRISTOL NEOK. 343
ward, since the more northern exposures on the island show that the sand-
stones and conglomerates are overlain l^y the dark-bluish shale, with only
a small interval of unknown rock. The most ready interpretation of this
fact is to suppose that the lower part of the Aquidneck shales is often coaly,
the thickness of this coaly section, however, being greatly variable.
Western Bristol Neck. — Bluisli aud grceuish Aquldueck shales form the main
mass of the Carboniferous rocks on Bristol Neck. Underlying them on
the southwest is a thick bed of sandstone, amounting to perhaps 50 feet
About 225 feet beneath this bed occurs more sandstone, of dark color, con-
taining coaly matter, and perhaps 150 feet beneath this level is coaly shale
with fern-leaf and Annularia impressions. If the eastward dip of 20° is
maintained, the conglomerate exposed at two localities above the main sand-
stone bed first mentioned lies about 250 feet above the latter. A short
distance above the conglomerate begin the greenish and dark-blue shales
of the Aquidneck series. The order of succession on the western side of
Bristol Neck is, therefore: coaly shale, gray or darker sandstone, bluish
sandstone, conglomerate with large pebbles, greenish and dark-blue shales.
If the great shale series of Bristol Neck be correlated with the shales of
Prudence Island and southern Conanicut, the underlying rocks may repre-
sent the upper part of the Kingstown series. Certain facts suggest a
relationship with at least the Prudence Island section. Pebbles containing
oboli are foimd in the conglomerate on the west side of Prudence
Island. While the pebbles of the conglomerate on the west side of Bristol
Neck are of much larger size, their lithological character agrees very well
with that of the Prudence Island pebbles, and oboli will no doubt be
eventually found there also. There is a considerable section of sandstone
on the west side of Bristol Neck. It is not interbedded with the con-
glomerate, but is found beneath it. The coaly shale on Bristol Neck, as
well as that on Prudence Island, contains plants, but the coal}^ shale on
Bristol Neck occurs, not at the base of the greenish and dark-blue shales,
but below the sandstones and conglomerates of that field. As a matter of
fact, however, these latter belong very high in the Kingstown series, and
strict parallelism of strata could hardly be expected at so great a dis-
tance as that from Prudence Park to western Bristol Neck, in a geological
field where lithological changes along the strike are frequent. Only a
general accordance could be demanded. For this reason the coaly shales,
344 GEOLOGY OF THE NAEEAGANSETT BASIN.
sandstones, and conglomerate of western Bristol Neck are considered as
belonging at the top of the Kingstown seiies. The sandstone exposures
on Popasquash Neck probably belong to the same horizon.
Rumstick Neck. — Tlic green shales of Rumstick Neck resemble the green
shales of western Bi-istol Neck and some of those of Prudence Island.
The sandstone underlying the same, offshore toward the southwest, contains
plant-stem impressions similar to those found in the sandstones beneath
the shales on the western side of Prudence Island The curve of the
strike of the sandstones suggests a shallow syucline pitching northward, and
a similar curve in the strike of the chief sandstone bed on the southwest
side of Bristol Neck suggests a similar structure there. The exposure on
Rumstick Neck is, however, too isolated to be safely correlated.
Kingstown sandstones equivalent to the lower part of the Coal Measures group, Jli the StnkeS Of
the coaly shales, the sandstones, and the conglomerates on the western
side of Bristol Neck be continued for any considerable distance northward,
rocks referred by Mr. Woodworth to the Seekonk section will be met. The
Kingstown series would therefore seem to correspond to the lower part of the
Coal Measures, including the Seekonk group, as limited by Mr. Woodworth
farther northward.
Triangular area of the Kingstown series in the Narragansett Basin, narrowing southward. PrOvided
that all the correlations so far made are correct, the following fact is brought
out. In the latitude of the Bonnet the Kingstown series occupies a width
of 3| miles. The eastern margin of the area occupied turns northeastward
at Beaver Head, with a direction of N. 38° E., as far as the eastern side
of Conanicut. At the latitude of Hammond Hill the series occupies a
width of at least 5 miles. At Hammond Hill the western margin of the
area turns northwestward, and in the neighborhood of Wickford Junction
the width of the area is about 8^ miles. According to this measurement
the eastern border of the area takes a more northerly course along the
east side of northern Conanicut. From Wickford Junction the western
border extends N. 23° E. to East Grreenwich, and the eastern border N.
24° E. along western Prudence Island to the eastern side of Popasquash
Neck. The width of the Kingstown area at East Greenwich, according to
this, is 8 miles. Nox'th of Coweset the western margin extends in a north-
western direction as far as southern Cranston, and thence N. 10° E. The
eastern margin may extend northward along the western side of Warren
THICKNESS AND POLDmG OP KINGSTOWN SERIES. 345
River. In that case the area invoh^ed has a width of at least 10 miles at
the northern limit of the Narragansett Bay map.
The increase in the width of the area occnpied by the Kingstown series
from 3 1 miles on the sonth to 10 miles on the north is of course striking
and demands some explanation.
Thickness of the series and evidence of folding. The tlllckneSS of tllC SeHeS Can be
measured with the greatest degree of certainty at its southern end, where
exposures are frequent and dips are steep. The total thickness of 11,500
feet there indicated may not equal that of the formation farther northward.
The steep dips in the area immediately north of a line connecting Quonset
Point, Wickford, and Wickford Junction, for instance, suggest a greater
thickness. So does the great east-west extension of the formation
northward. Unless in spite of the apparent uniformity of strikes and dips
over large areas there be in reality a system of repetition dufe to folding,
the thickness of the Kingstown sandstone group must in places greatly
exceed 11,500 feet. There is a little evidence in favor of such folding in
the portion of this region actually occupied by the Kingstown sandstones:
(1) Along the eastern side of Providence River, north of Riverside occurs
a synclinal fold, but this seems to disappear northward. (2) At Rumstick
Neck and on the southwestern side of the Aquidneck shale area on Bristol
Neck the trend of the underlying sandstones suggests synclinal folding.
(3) Prudence Island is a case of a well-marked synclinal fold. (4) The
steep dips, varying suddenly to lower inclinations, on the northwestern side
of Conanicut suggest crumpling of strata and possible folding. (5) The
shale area of southern Conanicut has evidently suffered folding, but the
character of this folding has not been well worked out. (6) Folds are
known in various parts of Aquidneck Island All of these facts suggest
folding also in the more western area occupied by the Kingstown sandstones,
but the direct evidence in favor of such folding is still wanting.
The view that the thickness of the sandstone series northward probably
does not greatly exceed 11,500 feet is also supported by the very low
general inclination of the strata over considerable areas, which tends to
reduce the estimates made in conformity with regions where the dip is
steeper. The very low general dips of most of southwestern Cranston and
Warwick have already been mentioned.
The dips on the western side of Bristol Neck are comparatively low.
346 GEOLOGY OF THE NA.REAGANSETT BASIN.
This is also true of the inclination of the strata on the westeni side of
Prudence Island and on the western side of Conanicut. The shale series
east of Mackerel Cove and on Freebodys Hill seems also to have low dips.
North of Barbers Height, toward Hamilton and northwestward, the dips
also become lower, indicating a greater horizontal extension of the series
for the same thickness of strata than exists farther southward. The evi-
dence on Potowomut Neck is in favor of low dips.
If these areas of low dips among those of higher dips can be con-
sidered as evidences in favor of a system of local folding, at present only
obscurely known, it will not be necessary to assign any extravagant thick-
ness to the more northern portion of the Saunderstown series.
Rocky Point conglomerate and its connection with the estimate of the thickness of the northern section.
Unfortunately, the estimate of 11,200 feet for the Kingstown series in south-
western Craftston and in Warwick does not offer a means of comparison
with the more southern section noted above, because (1) it does not include
the Rocky Point conglomerates, supposing that the latter lie at the top
of the Kingstown sandstone series, and (2) it is not determinable that the
rocks immediately beneath the Rocky Point conglomerates belong to the
sandstone series, for the reason that the age of the Rocky Point conglom-
erate is not known with certainty. In the field investigated by the writer
there is no evidence militating against the belief that these conglomerates
correspond to those which begin to occur near the top of the Aquidneck
shales as exposed northeast of Warren, and which are there an introduc-
tion to the Dighton conglomerates. In the area north of that investig'ated
by the writer, the Rocky Point conglomerates, or rather their supposed
equivalents, seem to occur at a horizon corresponding more nearly to the
top of the Kingstown sandstone series, similar to the conglomerate of
western Bristol Neck and western Prudence Island. This is equivalent to
placing them on the horizon of the Seekonk group of Mr. Woodworth,
which includes also the series of shales, sandstones, and medium conglom-
erates into which the Aquidneck shales merg-e north of Warren.
Chief features of the Kingstown series. TllC KiugStOWU SaudstOnC SCricS may bc
desci'ibed as a complex consisting of alternations of shale, sandstone, and
conglomerates. The conglomerates are usually made up of very small
pebbles. Near the base of the section, however, in the basal arkoses and
associated rocks there occur layers with large pebbles. Toward the top of
FOSSILS IN KINGSTOWN SEEIES. 347
the section conglomerates come in again. These are seen at the western
margin of Beaver Head, 0:1 Dutch Island, the western side of northern
Conanicut, the western side of Prudence Island, and the western side of
Bristol Neck; and apparently the conglomei-ates at Rocky Point and the
eastern side of Providence River belong at this horizon. (See the para-
graph on the equivalence of tlie Kingstown and Aquidneck series, on
p. 361.)
Fossil-plant localities, — Coaly slialcs witli fem impressions occur .as follows:
About 2,000 feet above the base of the series are the coaly shales of
Sockanosset Hill, inclosing fern leaves. At the top of the series and at
several points farther down are more carbonaceous shales, also containing
fern impressions. The highest beds with plant remains in the Kingstown
series are the conglomerate and sandstone beds exposed on the western
side of Prudence Island. The coaly shales just above belong to the base
of the Aquidneck bed. On Beaver Head the shales in the upper part of
the Kingstown series do not preserve the fern impressions. The fossil
locality on the eastern side of northern Conanicut probably belongs a little
above this horizon. A slightly lower horizon is occupied by the exposm'e
of fern-bearing coaly shales on the west side of Bi'istol Neck. A still lower
one includes the fossil-fern locality on the western side of Dutch Island and
the locality discovered by Prof T. Nelson Dale on the western side of
northern Conanicut. A comparison of the ferns from the upper and lower
horizons might show variations in the flora, giving suggestions as to means
of recognizing- the same horizons observed in the field.
Plant stems are found above the level of the lowest coal horizon at
Hills Grove and near the top of the section on the western side of Prudence
Island, and possibly the exposures off the end of Rumstick Neck and along
Providence River, in all cases consisting of sandstones belonging to the
same horizon. Indeed, the upper half of the Tenmile River section of
Mr. Woodworth appears to be in places rich in calamites.
Ferns occur again in the overlying Aquidneck shale series and in the
coaly shales interbedded with the coarse conglomerate series at the top of
the Narragansett Basin Carboniferous section at Castle Hill, as will be
described later, demonstrating that all of the exposures here described, from
the basal conglomerates and arkoses to the top of the Purgatory conglom-
erate, are Carboniferous.
OHAPTEKA^III.
THE AQUIDNECK SHALES.
AREA OCCUPIED BY THE AQUIDN^ECK SHAEE SERIES.
East of the complex of rocks called the Kingstown sandstones, owing to
the characteristic and frequent appearance of sandstone beds in the section,
lies an equally great area, in which shales form almost all of the exposures,
excepting where synclinal folding has allowed an overlying conglomerate to
be locally preserved. The shales of this eastern area contain isolated sand-
stones and thin conglomerate beds, but the latter are so rare that the term
"shale series" has peculiar force in designating the general lithological
character of the rocks in question. The shales occupy (1) the southern half
of Conanicut Island as far north as Round Swamp, excepting (a) the small
area included in Fox Hill, already described as the top of the Kingstown
section, and (b) a small area of arkose on the east side of Mackerel Bay,
north of the granite hills. They form (2) the southern and larger division
of Prudence Island (PI. XXIII), excepting the western margin of the island,
north of Prudence Park. They are frequently exposed (3) in almost all of
Bristol Neck, north of the granite area, only the most western exposures on
the neck belonging to the Kingstown series. The shales form also (4) almost
the whole of Aquidueck Island, excepting (a) at the top of the syncline south
of Butts Hill, and in those areas occurring along (b) the southeast shore of
the island at Woods Castle, (c) in the Paradise-Purgatory region, (rf) at the
Newport Cliffs, (e) on Miantonomy Hill, and (/) at Coddington Point, where
the overlying conglomerates prevail. The (g) pre-CarboniferoiTS rocks of
the Newport Neck region must also, of course, be excluded. Owing to the
abundant exposures of the shales on Aquidneck Island and the belief that
all these shales form one great series, the Aquidneck exposures are considered
typical, and the shale series wherever exposed is therefore called the
Aquidneck shale series.
348
THE AQUIDNEOK SHALES. 349
SOUTHERN CONANICUT.
The shales on Conanicut form a singularl}^ uniform series. Owing to
abundant cleavage, they are everywhere strongly fissile, splitting into thin
plates. The color is usually dark blue, appearing nearly black where
moistened by water, and more brownish or greenish brown where very dry.
But variations from greenish to nearly black occur also, entirely aside from
any question of moisture, the darkening of color being due to the amount
of carbonaceous material present. This gives rise to an alternation of
darker and lighter color bands, which is very characteristic of the shales in
many parts of Conanicut, and without which it would rarely be possible to
determine the plane of stratification of the rock. Not a trace of conglomerate
or of coarse sandstone has so far been found in the shale series of Conanicut.
Thin layers of a very fine-grained whitish sandstone occur along the
southern margin of Dutch Island Harbor, along the shore east of Fox Hill,
and on the eastern shore along Freebodys Hill. Where there is no color-
banding or whitish sandstone there is no means of learning the real dip
and strike of the shales, the cleavage obscuring all traces of stratification.
The dips on the western side of Conanicut are certainly, in places, very
steep to the westward, practically vertical, but at the first exposure south of
Fox Hill the dip is between 45° and 60° E., and this, in connection with
tlie general eastward dip of the strata on Fox Hill, is one of the main
reasons for believing that the Aquidneck shales overlie the Saunderstown
sandstones.
On the eastern side of the western division of the island — i. e., along
the western side of Mackerel Cove and thence southward — the dips are
usually eastward at angles which are frequently as low as 45°, and some-
times much lower. On the eastern side of Mackerel Cove the dip is low to
the east. On Freebodys Hill some of the dips are nearly horizontal, others
are low to the east, and in places the dip is very variable. So little being
known of the geological structure of the island, it is impossible to form a
close estimate of the thickness of the shale series exposed there. A mini-
mum estimate would be 2,000 feet, while 4,200 feet can not be called a
maximum for the entire series, considering the steep dips on the western
side of the island. The coaly shales on Fox Hill, at Beaver Head, may be
considered as forming a transition series between the Kingstown sandstones
beneath and the Aquidneck shales above.
350 GEOLOGY OF THE NAERAGANSETT BASIN.
PRUDENCE ISLAND.
In the case of the coaly shales on the western side of Prudence Island,
it is equally probable that these shales indicate the beginning of the great
Aquidneck shale series immediately overlying them. On the western side
of Prudence Island the Aquidneck shales proper are of a dark-blue color,
like those on Conanicut and Aquidneck islands. The few exposures above
the sandstone series a mile north of Prudence Park suggest that sandstone
layers are, however, a more common element in the shale series here than on
Conanicut. The same observation also applies to the exposures south and
southeast of Potters Hotel (which is located on the highest point of the
island), where sandstones and even some thin conglomerate layers occur.
Color banding is not seen on the western side of Prudence Island, but on the
eastern side, about two-thirds of a mile north of the light-house on Sand Point,
color-banded shales like those on Conanicut are well exposed (PL XXII).
South of the light-house the shales are sericitic, and not so fissile, or at least
usually not partially separated along the cleavage into thin plates, as they are
elsewhere, yet it is evident that these shales of eastern Prudence Island could
also be readily split parallel to the cleavage prodviced by the abundant pres-
ence of this micaceous mineral. An unusual feature is the frequent presence
south of the light-house of sandy courses, from 8 to 12 and even 20 inches
in thickness, some of which merge into thin conglomerate beds. One or two
of the pebbly beds attain a thickness of 2 or 3 feet and constitute a genuine
conglomerate. The color of the shale on this eastern side of Prudence Island
is more inclined toward the greenish hue of the shales at Eastons Point
than toward the dark blue so common on Conanicut Island. A few more
carbonaceous shale layers occur intercalated among the greenish beds
The eastern Prudence Island exposures south of the hght-house there-
fore present more frequent variations from the dark-blue color and tissile
structure of the Aquidneck shales, and show more frequent sandstone and
conglomeratic layers, than do these shales on southern Conanicut or southern
Aquidneck. Sandstones and thin conglomerate beds are fairly frequent,
however, on Aquidneck or Rhode Island, directly east of the Prudence
Island exposures just described; also in the area from Coggeshall Point to
McCurrys Point and thence northward to within half a mile of Butts Hill.
These facts suggest an increase in the amount of sandstone, and even the
THICKNESS OF AQUIDNECK SHALES OP PRUDENCE. 351
introduction of cong-lomerate, in the lower part of the Aquidneck shales on
going northward.
THICKNESS OF THE SHALE SERIES ON EACH SIDE OP THE PBUDBNCE ISLAND
SYNCLINE.
The structure of Prudence Island is a syncline, the sides dipping 20°
to 25° E. on the west side (PI. XXIII), and 70° to 80° W. on the east side.
The bottom of the syncline appears to be at Potters Hotel or to the west-
ward. The thickness of shales forming the western side of the syncline as
far as exposed may be 2,200 feet. The thickness included in the exposures
forming the eastern side of the syncline appears with more certainty to be
at least 1,750 feet. In that case the lower 450 feet exposed on the western
side of the syncline may not be exposed on the eastern side of the island.
Since these estimates are not based on a continuous series of exposures in
an east-west direction, there being no exposures for almost a mile west of
Potters Hotel, the figures given can not have great value, although they
serve to give at least some notion as to the probable minimum thickness of
the shale formation. The sandstones and conglomerates on the western
side of Prudence Island north of the wharf being assigned to the Kingstown
series, it is evident that the Aquidneck shale series as exposed on this side
of the island overlies the Kingstown series. For this reason the western
part of the Prudence Island section is believed to furnish evidence in favor
of the more recent age of the Aquidneck shale as compared with the Kings-
town sandstones. This corroborates the evidence furnished by the Beaver
Head section on Conanicut.
BRISTOL NECK.
The greenish, dark-blue, and greenish-blue shales of Bristol Neck are
known to dip low eastward on the western side of the neck. If the sand-
stone and conglomerate beneath the shales on the west belong to the
Kingstown sandstones, the more recent age of the Aquidneck shales is
here indicated once again. A sandstone layer, becoming conglomeratic
near the Warren-Bristol road, occurs in the shale series about 400 feet
above the coarse conglomerate layer at the sujjposed base of the shales,
and thus shows the existence of occasional sandy and conglomeratic layers
in the Aquidneck shale series northward. Sandstone layers are not known
352 GEOLOGY OF THE NARRAGANSETT BASIN,
to occur elsewhere in tlie Aquidneck shales of the neck. The dip of the
stratification of the shales over the middle and eastern part of the neck can
not be determined with certainty. Under these circumstances there is no
sufficient evidence from which to estimate the thickness of the Aquidneck
shales here exposed; 1,700 feet would appear to be a very moderate esti-
mate; 2,700 feet may be excessive. The low dips of the sandstone and
conglomerate on the western side of Bristol Neck, and the low dip of the
coarse conglomerate on the western side of Warren Neck, taken in connec-
tion with the small east-west extent of the lines of exposure of the
Aquidneck shale series, have caused the writer to believe that the shale
series was not so thick on Bristol Neck as it is farther southward, aiid that
probably the Aquidneck shales diminished in thickness in passing northward
from southern Aquidneck Island into Bristol Neck.
AQUIDNECK ISLAND.
The Aquidneck shales are typically exposed (1) in the Glen and (2)
in the valley south of McCurrys Point on the east side of Aquidneck, or the
Island of Rhode Island; also (3) in the valley east of Coggeshall Point,
(4) in Lawtons Valley, and (5) in various stream beds, railway cuts, and
shore exposures as far south as Coddington Point and in the railroad cut
west of Beacon Hill, both on the western side of the island. The Aquid-
neck shales form by far the greater part of the stratified rocks of the island.
They are characteristically dark blue, and usually do not show color band-
ing, which is also true of the Bristol Neck exposures. Thin fine-grained
sandstone beds occur not only in the shale series northward, but also in
the middle and southern part of Aquidneck, where the shale series is most
typically developed, so that the Conanicut shales are at one extreme lith-
ologically of the shale series, in presenting hardly any sandstone layers at all,
none of those existing being even coarse, while the eastern Prudence Island
and the northern Aquidneck exposures, just east of the Prudence Island
exposures, are at the opposite extreme, containing more or less interbedded
thin sandstone and some conglomerate layers. On Aquidneck Island thin
medium-grained sandstone beds occur in the shales {1) at the north end of
Coddington Neck and (2) along the main Newport- Bristol Ferry road a short
distance south of Lawtons Valley. Coarse sandstone, merging in places
into a very small-pebbled conglomerate, is found (3) east of the railroad
THICKNESS OF SHALES OF AQUIDNECK ISLAND. 353
half a mile south of Lawtons Valley, and a series of exposures containing
sandstone extends (4) from the valley east of Coggeshall Point for at least
half a mile northward. Sandstone layers are also exposed (6) along the
middle third of the coast both on the east and on the west side of the
island, and a bed is also located (6) in the lower part of the Glen valley.
Sandstone occurs rather frequently in the shale series (7) for a mile south
of Coggeshall Point, and both sandstone and small-pebbled conglomerate
layers occur (8) along the eastern shore from McCurrys Point to the expo-
sures east of Butts Hill.
THICK:NrESS OF THE SHALE SECTION EAST OF THE PORTSMOUTH
SY]SrCLINE.
The geological structure of the shale area over the northern third of
Aquidneck Island is evidently that of a syncline, the base of the syncline
passing beneath Butts Hill and extending a little west of south toward the
west of Quaker Hill. The dip on the eastern shore of the island varies
between 20° and 40° W., and at the mine northeast of Butts Hill it is
about 20° W. According to this the coal seam opened at the eastern
coal mine could hardly be more than 500 or 570 feet above the shore
exposures along the northern third of Aquidneck, while the coarse con-
glomerate south of Butts Hill, and elsewhere at the same level in the
syncline, can hardly be more than 500 to 650 feet higher. According to
this the shale section exposed on the east side of the syncline probably
averages somewhere between 1,000 and 1,220 feet, but may be a little less
than 1,000 feet in thickness, and might possibly exceed 1,300 feet.
PROBABLE THICKNESS OF THE SHALE SECTIOlSr WEST OF THE
PORTS3IOUTH SYISTCLIIVE.
Along the shore north of Coggeshall Point the dip appears to be low
to the east, usually not exceeding 20°. Farther east the dips are steeper to
the east, varying most frequently between 45° and 60° E. According
to this the coarse sandstone layer on the brow of the hill east of Cogges-
hall Point lies about 1,300 to 1,500 feet beneath the level of the coarse
conglomerate; the shore exposures lie between 1,300 and 1,500 feet lower
and the western mine exposures occur apparently at a still lower level, per-
haps 400 to 500 feet beneath. According to these estimates the western
MON XXXIII 23
354 GEOLOGY OF THE NAREAGANSETT BASIF.
coal beds lie between 3,000 and 3,500 feet beneath the coarse conglomerate,
while the eastern bed lies between 500 and 570 feet beneath the conglom-
erate, so that eastern and western coal beds do not belong to the same hori-
zon, but one imderlies the other about 2,500 to 2,900 feet. It should be
remembered, however, that these estimates ar^ made without a knowl-
edge of the results obtained by a series of diamond-drill borings made west
of the eastern mine within recent years. The apparent failure to detect on
the western side of the syncline the coal bed which was worked in the
eastern mine also suggests either that the bed thins out westward or that
it has so far not been discovered on that side of the syncline.
LITHOIjOGICAr, VARIATIONS IK THE SHALE SERIES.
The appearance of frequent sandstone beds and an occasional con-
glomerate layer on the eastern shore, east of the Portsmouth s}mcline, and
the exposure of only one or two coarse sandstone beds on the western side
of the syncline, on the brow of the hill east of Ooggeshall Point and
northward (according to preceding calculations approximately at the same
level), suggests that there may be a reduction to the westward of the
amount of sandy material at this particular horizon. In a general way
also there appears to be more carbonaceous material in the shale series on
the east side of the Island of Aquidneck than at corresponding heights
westward, and there is certainly less carbonaceous material in the shale on
Prudence Island and on Bristol Neck than eastward. Observations of this
nature have little value, however, since the recorded strikes and dips are
not sufficient in number to give assurance regarding the strike and dip of
the intermediate localities, where exposures fail or where the stratification
has been obscin-ed by cleavage.
GEOLOGICAL STRUCTURE OF THE MIDDLE THIRD OF AQUIDNECK
ISLAND.
From McCurrys Point to the exposures half a mile north of Black
Point, little can be determined about the dip of the rocks. In the Glen a
sandstone layer appears to be nearly horizontal. Nothing satisfactory could
be determined about the dip of the exposures along the road from Slate
Hill south westward. North and south of Lawtons Valley, and at several
STEUCTURE OF AQUIDNEOK SHALES. 355
points along the western shore, the dip, however, is distinctly eastward.
Over this more eastern part of the middle third of Aquidneck Island the
strata are beheved to be inclined at a low angle, and to form a series of
low folds, leaving the rocks in general essentially horizontal. Along the
western coast, however, and for a distance of a mile or more east of the same,
more marked eastward dips occasionally occnr, and here the folding may
be more pronounced, although the recorded observations so far fail to give
evidence of marked folding.
STRATA PROBABLY FOLDED.
If the coarse conglomerates of Coddington Point, Coasters Harbor
Island, and Miantonomy Hill correspond to the coarse conglomerates in the
northern third of the island, it is evident that, in spite of the eastward dips
so far recorded from the western Portsmouth mine as far as Coddington
Point, there must be some system of folding as yet not discovered, which
(1) allows the Miantonomy Hill exposure of conglomerate to appear to the
west of the line of strikes shown by the shales to the northward, while they
are still evidently above the Aquidneck shales as exposed near the hill; (2)
the fact that the Coasters Harbor Island and the Coddington Point expo-
sures of coarse conglomerate lie at least 1 00 feet beneath those at Mianton-
omy Hill suggests that there must be folding between these localities, if
the two sets of coarse conglomerates are to be considered as of the same
age, and the exposures at Coasters Harbor Island and Miantonomy Hill
favor that view.
The synclinal structure of the southern half of Prudence Island and
the northern third of Aquidneck Island demands anticlinal structure in the
region between. How far south either the anticline along the Eastern
Passage or the syncline of Prudence Island extended is unknown. Are the
coal beds in the western mines near the base of the Aquidneck shale series?
Do these coals thin out westward! Are the coaly shales on the western
shore of Prudence Island the representatives, in a general way, of the
thicker coal beds at the Portsmouth mine! Do the coaly shales of Gould
Island belong to the same horizon — i. e., that of the Portsmouth mine coal
beds! These are questions which can not be satisfactorily answered in the
present state of our knowledge.
356 GEOLOGY OF THE NAEEAGANSETT BASIN.
GOULD ISLA>^D or THE 3IIDDLE PASSAGE.
The strike of the strata composing Gould Island is generally north-
south. Plumbago and coaty shales form almost all of the shore exposm'es
on the eastern shore for a little more than half the length of the island,
going southward. Farther south carbonaceous shales continue to appear,
but sandstone, in part conglomeratic, also makes its appearance. The peb-
bles of the more conglomeratic layers are very small. The dips are chiefly
east, but very irregular, and the most northern dip appears to be westward,
while the strata about a fourth of the length of the island north of its
southern end are nearly vertical.
SOLTTHERIS^ THIRD OF AQLIDKECK ISEAIN^D.
South of the line connecting Coddington Point and Black Point, includ-
ing the southern third of Aquidneck Island, the t3'pical dark-blue and
greenish-blue shales of the Aquidneck series are not often exposed (see foot-
note on page 372). The top of the series is exposed at Eastons Point, but
presents features which it is desirable to discuss in connection with other
exposures farther north that seem to belong to the same horizon. This will
be done under the next heading.
UPPER GREEX SHAEES OF THE AQUIDXECK SERIES.
The great mass of shales exposed on Aquidneck or Rhode Island
undoubtedly constitute a single series. Considering their thickness and
their considerable geographical distribution, they present decided litho-
logical uniformity. Along the middle of Aquidneck Island, however, the
upper part of the shale is greenish in color, in contrast to the chiefly dark-
blue fissile shales underneath. These green shales are well exposed (1)
for a mile along the western road from Newport to Bristol Ferry, south-
west of Butts Hill, on the western side of the Portsmouth syncline. They
are seen again (2) half a mile southwest of the top of Quaker Hill, on the
eastern side of the syncline. The green shales include near the top more
sandy layers and sandstones, followed liigher up by the sandstones and
conglomerates of the conglomerate series. At (3) Slate Hill and for over
a mile southwestward along the road green shales are again exposed. The
coarse conglomerate series which is supposed once to have overlain them is
SANDSTONES WEST OF SAKONNET EIVEE. 357
no longer present, and if ever in existence here must have been removed
by erosion. At (4) Eastons Point greenish shales verging to bluish are well
exposed beneath the coarse conglomerate on both sides of the anticline.
The greenish shales of all these localities are believed to represent the top
of the great Aquidneck shale series. This does not mean that all of the
greenish shales elsewhere also belong to this upper horizon. The greenish
shale of the western part of Bristol Neck certainly belongs low in the shale
series, and not at the top, but along the middle length of Aquidneck Island,
from the Portsmouth syncline to Eastons Point, such a north-south line of
green shales near the top of the Aquidneck shales can be recognized.
SAKONNET SAISTDSTONES OF THE AQUIDNECK SERIES WEST OF THE
RIVEK.
West of the Hue of upper green shales just described the corresponding
upper layers of the Aquidneck shale series are not greenish in color, but show
the more usual dark-blue tinge. This is certainly true beneath the Mian-
tonomy Hill and Coddington Point conglomerates, where the underhung
shales seem to represent the same horizon. Eastward of the line of upper
green shales described there are other exposures of the upper shales of the
Aquidneck series, which are also occasionally green in color — for instance,
north of the conglomerate area at Fogland Point. But usually the more
eastern exposures of the upper Aquidneck series fail to show a marked
shaly character; on the contrary, they more frequently become more
sandy in some of their layers, or even take on the general character of a
sandstone series, in which shales form only the subsidiary beds. When this
occurs, the finer sandstones usually contain considerable carbonaceous
material. Such shales with a predominating amount of dark-gray or
blackish sandstones are found at the top of the Aquidneck shale series and
beneath the coarse conglomerates along the shore north of Black Point,
and to a less pronounced degree at Taggarts Ferry. The more sandy
character of the upper part of the Aquidneck series along the southeastern
side of the island may indicate approach to shore conditions in that direction.
THICKlSrESS OF THE UPPER GREEN SHAEES.
The thickness of the upper green shales on the western side of tlie
Portsmouth syncline is probably at least 150 feet, and this is certainly the
smallest possible estimate for the thickness of the green shale series exposed
358 GEOLOGY OF THE NAERAGANSETT BASIK
at Slate Hill and southwestwarcl. The exposed portion of the shales
beneath the conglomerates at Eastons Point adds up, according to Prof.
T. Nelson Dale, to at least 600 feet, with an unknown thickness of shales
beneath, but even the shales exposed can not all be called green. The
thickness of the upper green shales must occasionally equal 200 to 250 feet.
THICKNESS or THE SAKOjSTSIET SANDSTONES.
The upper sandstones and shales beneath the conglomerates at Black
Point have a thickness of at least 110 feet, while their total thickness at this
point is evidently greater. The corresponding series at Taggarts Ferry
can, however, hardly exceed that amount. Their thickness east of the river
is discussed later.
The thickness of the more typical dark-blue Aquidneck shales probably
exceeds 3,000 feet. The upper green shales and the Sakonnet sandstones
do not add considerably to this thickness, so that an estimate of 3,000 to
3,500 feet for the Aquidneck shale series seems reasonable^ Desirable as it
would be to secure a better idea of the total thickness of the Aquidneck
s|iales, this is at present impossible. The accessible data do not furnish the
means for such an estimate.
NOETHEEN EXTENSION OF THE AQUIDNT:CK SHAEES.
North of Bristol Neck the Aquidneck shale series seems to lose its
identity. Greenish-blue shales continue to be exposed at several points a
mile north of the Warren and Fall River Railroad, but on continuing north-
ward are soon intercalated with sandstones and conglomerates to such an
extent that they can no longer be recognized as a distinct series, but
evidently merge northward into the upper part of Mr. Woodworth's lower
Coal Measures series.
EQUIVALENTS OF THE KINGSTOWN SANDSTONTE AND AQUIDNECK
SHALE SEEIES NOETHEAST OF WAEEEN NECK.
East of Aquidneck Island and Bristol and Warren necks it appears
impossible to distinguish between a lower Kingstown sandstone and an
upper Aquidneck shale series. Sandstones and shales are exposed below
the coarse conglomerates southwest of Swansea village. Coaly shales are
SANDSTONES EAST OF SAKONNET RIVER. 359
found five-eigliths of a mile north of South Swansea Station. Shaly sand-
stones occur west of Lees River north of the raih-oad. At Bi-aytons Point
very coaly shales and some sandstones are exposed. Northeastward, on
Sewammock Neck, sandstone is found. The exposures east of Taunton
River inchide the arkoses resting upon pre-Carboniferous granites, both of
which will be discussed later.
The section included between the coarse conglomerate of Swansea vil-
lage and the arkoses of Steep Brook or Fall River must correspond in some
measure to the Aquidneck shales and possibly to more or less of the Kings-
town sandstones as described from the main area of the basin toward the
southwest. If the section from Swansea village to Steep Brook be consid-
ered as simple in geological structure, tolerably free from local folding
or marked changes of dip, a supposition by no means certain, fair esti-
mates might be made as to its thickness. If the strata be supposed to be
inclined toward the northwest at an average angle of 45°, a thickness of
10,600 feet would have approximate value, while at an inclination of 60°
the thickness of section might equal 13,800 feet. The thickness of the
Kingstown sandstones was placed above at 11,500 feet, and that of the
Aquidneck shales at 3,000 to 3,500 feet, making a total thickness of 14,500
to 15,000 feet for the corresponding strata farther southwest. Unfortunately
all these estimates are based on data either not strictly reliable or even not
fairly satisfactory, especially since in the regions where the estimates are
made there are areas where exposures are few, but these estimates are at
least the best at present available. While it is impossible to distinguish an
upper Aquidneck shale from a lower sandstone series between Swansea
village and Steep Brook, yet the existence of abundant shales in the upper
part of this section should be distinctly recognized as an approach to the
lithological distinctions in existence farther southwestward.
SAKOKXET SAKDSTOlSrES OX THE EAST SIDE OF THE RIVER.
That the upper part of the Aquidneck shales, that portion immediately
underlying the coarse conglomerate series, loses its shaly character and
assumes more of a sandstone nature eastward has already been noted in
speaking of the exposures north of Black Point and at Taggarts Ferry, on
the southeastern shore of Aquidneck Island. On the eastern side of the
Sakonnet River, east of Aquidneck Island, the rocks underlying the coarse
360 GEOLOGY OF THE NAERAGANSETT BASIN.
conglomerate series consist also chiefly of sandstone. Some of the sand-
stone layers contain scattered pebbles, or even thin streaks of conglomerate;
conglomerates with pebbles of moderate size also occur, but do not consti-
tute an important element of the Sakonnet sandstones. Shaly layers are
more common, and occasionally attain considerable thickness — for instance,
in the case of the coaly shales along the shore directly west of Windmill
Hill. As a rule, however, the sandstones predominate very miich at this
horizon. The sandstone exposures north of High Hill, and the sandstone,
shale, and fine conglomerate extending from the shore west of Windmill
Hill nearly to Browns Point, are characteristic exposures of this Sakonnet
sandstone on the east side of the river. The shales and sandstones south
of Corys Wharf may possibly represent some lower horizon in the Aquid-
neck shale series.
ABSENCE OP THE SHALE SERIES BENEATH THE COABSE CONGLOM-
EEATES EAST OF THE SAKONNET RIVER.
The upper Aquidneck shales are therefore believed to merge into
sandstones on approaching the present eastern border of the Carboniferous
basin. And this may be true also of the lower horizons of this series. If
the coarse conglomerates on the eastern side of the Sakonnet River be,
indeed, the equivalents of the coarse conglomerates on Aquidneck Island and
northwest of Taunton River, and if the sandstones just mentioned belong
to the Sakonnet series as interpreted west of the river, very little space
intervenes in most localities on the east side of the Sakonnet River between
these conglomerates and sandstones and the basal arkose layers and coaly
shales. The section east of the Sakonnet River must have had a somewhat
different historj?- from that on the mainland west of the bay. An extensive
system of irregular faulting would seem to oifer a possible explanation for
this sudden diminution of the Aquidneck shale and Kingstown sandstone
section. The irregularity of the dip and strike of the coarse conglomerate
exposures and .their areal distribution would seem to favor the existence of
marked local faulting. But it is also possible that the basal arkose east of
the bay is not identical in age with that west of the bay. It may belong
to a higher horizon, possibly corresponding to part of the Aquidneck shale
series. In that case the failure of any equivalent of the Kingstown sand-
stone series to appear east of the bay is not so surprising.
DISTRIBUTION OF AQUIDNECK SHALES. 361
WEDGE-SHAPED AREAL DISTRIBUTION OF THE AQUID^TECK SHAEE
SERIES.
If the King-stowu series may be compared with a wedge tapering
southward, the Aquidneck shales may be said to form a wedge-shaped area
tapering northward, at least as far as Bristol Neck. From the northern end
of this wedge-shaped mass a narrower area extends northeastward toward
Taunton River. This wedge-shaped areal distribution suggests a general
inclination of the southern part of the Carboniferous formation toward the
south-southeast, a feature possibly to be studied in correlation with the south-
ward pitch of the rocks involved in the various coarse conglomerate synclines
and anticlines found in the southern third of Aquidneck Island. The pecu-
liar combination of northeast with more northerly boundary lines between
the sandstone and the shale series finds expression elsewhere in the sudden
changes in the direction of the shore line on the various islands, in the strikes
of the chief cleavage planes, and, to a certain extent, in the trends of the
hills. These facts suggest that the Carboniferous series has been subjected
to two systems of folding, making moderate angles with each other, the one
causing folds trending more nearly north-south and the other east of north.
EQUIVAEE:tirCE OF THE KINGSTOWK SANDSTONES AND THE AQUID-
NECK SHAEES.
A reference to the map will show that the identifiable Kingstown
sandstones are confined to the western side of the Narragansett Basin, while
the Aquidneck shales belong to the middle area, so that the Kingstown
sandstones border in a general w&j the Western Passage of the bay, while
the Aquidneck shales border the Eastern Passage and a pai-t- of the Sakon-
net River. It has therefore several times been a serious question whether
these two formations may not be equivalent, the western Kingstown sand-
stone and shale series passing toward the east into a typically more shaly
Aquidneck phase. An interpretation of this kind would much simplify the
conception of the geology of the southern part of the Narragansett Basin.
Unfortunately there are insuperable difficulties of observation at the very
point where the transition between these two formations should be traced.
The exposures along the Bonnet, those on Dutch Island, which do not lie
far above the same, and the rocks along the western shore of northern
Conanicut, along Slocums and Great ledges, all e\ddently belong to the
Kingstown series, while the shales on southern Conanicut, from Beaver
362 GEOLO&Y OF THE NARRAGANSETT BASIjST.
Tail to Mackerel Cove and Dutch Island Harbor, probably even as far as
Potters Cove, north of Freebod}^ Hill, belong to the Aquidneck shales. At
the former localities, sandstones and even small-pebbled conglomerates are
fairly common, while at the latter conglomerates and coarse-grained sand-
stones are altogether unknown, and sandstones of any description are
exceedingly rare. Nothing could be in greater contrast than the exposures
on Fox Hill and those on the main body of Conanicut from Freebody Hill
to Beaver Tail. There is no transition between the Kingstown series and
the Conanicut shales in this region. The dissimilarity here is indeed far
greater than farther northeast, where the Aquidneck shales contain more or
less sandstone. Sandstones and even a little conglomerate occur, for
instance, in the Aquidneck shales of Prudence Island, and in the shales on
Aquidneck itself, especially near the base of the formation. Sandstones
form a few widely distant beds also at higher altitudes in the shale series
on Aquidneck Island, but sandstones are not common in the upper beds
until the Sakonnet sandstones are reached. However, neither on Prudence
Island nor on Aquidneck Island is it possible to recognize a transition,
either lateral or vertical, from the Kingstown into the Aquidneck series.
The Aquidneck shale series is therefore most distinct from the Kings-
town sandstone in the areas where the two series are most typically
developed — at the nearest point of approach of these areas, at Fox Hill on
Conanicut Island; and on the western side of Prudence Island the dips
indicate that the Aquidneck shales overlie the Kingstown sandstones, and
for the present the conclusion must be that the shales overlie the sandstone-
shale series, and this has been the interpretation in this monograph.
This does not, however, overlook the facts that the shale series on
Prudence Island msij contain rather frequent sandstone and some con-
glomerate beds, that on Aqiiidneck Island they may contain many sand-
stone beds near the base and a few higher, and that in Cranston, East
Providence, Swansea, and northward they contain so much sandstone, and
even conglomerate, that the two formations can no longer be distinguished,
but are merged into a general Carboniferous series of shales, sandstones,
and to some extent conglomerates.
The distinction between Kingstown sandstones and Aquidneck shales
therefore disappears in the northern part of the area comprised in the
bay region of the Narragansett Basin, but the difference between these
rv '^" ' - . ■' ■
'•■
^.
* ■ ■,•'''
;
i^u^
' ' " ^'■-
FOSSILS OF AQUIDNECK SHALES. 363
formations farther south is sufficiently marked to warrant their separation
in this part of the report.
It is not impossible that the Kingstown series is not at all exposed east
of the Eastern Passag-e. The section between the coarse conglomerates
and the basal ai'koses is evidently much smaller there than on the western
side of the bay, and no exposures assignable to the Kingstown series are in
direct evidence.
The Aquidneck shales on the southwestern margin of Prudence Island
have weathered in an irregular manner, producing many small cavities
upon the surface of the shales, giving the appearance of irregular fretwork
(PL XXIV).
FOSSILS OF THE AQITIDNECK SHALE SERIES.
Fossils are found in the Aquidneck shales at various horizons. The
fossiliferous horizon at their very base has already been mentioned — for
instance, in the case of the coaly shale on the western shore of southern
Prudence Island. The western Portsmouth mine exposures of northern
Aquidneck possibly represent a somewhat higher horizon, fern impressions,
calamites, and Sigillai'ia occurring there. Next comes the fern locality near
the termination of Corys Lane, on the western shore of the island; then
the locality just east of the railroad in the gnlly half a mile north of Law-
tons Valley, where a few ferns were found; next, a mile southeast of Carrs
Point, on the western Newport- Bristol Ferr)^ road. The fern impressions
found half a mile south of the wharf on the eastern Portsmouth shore, and
those found a short distance north of the Glen, may belong to about the
same horizon. The fern impressions found along the roadside tlii-ee-fourths
of a mile northeast of Butts Hill probably represent a higher horizon.
Those at the northern side of the Old Fort, on the side north of Butts Hill,
are still higher in the series. If the conglomerates at Coddington Point
belong to the group of coarse conglomerates overlying the Aquidneck
shales, the fern impressions near the northern end of the point represent a
horizon above their base. The fern locality along the coast a mile and a half
north of Coddington Point at present can not be well located stratigraph-
ically. The same statement applies with greater force to the fern locality
on the western side of Braytons Point, which consists of coaly shales, such
as exist near the top of the sandstone series in the more western parts of the
bay region, but the jjrecise stratigraphic position of the deposit is unknown.
CHAPTEE IX.
THE PURGATORY CONGLOMERATE.
Coarse conglomerate overlying the Aquidneck shale series. TllG KuigStOWn Sei'ieS IS OVei'-
lain by a considerable thickness of sliales, here termed the Aquidneck
series. These shales retain their shaly characteristics and bluish-black color
to within a very short distance of the base of the overlying coarse conglom-
erate at Coasters Harbor Island, Coddington Point, and Miantonomy Hill.
Farther eastward, near the top of the Portsmouth syncline, at Slate
Hill and southwestward, and to a less degree on both sides of the Eastons
Point anticline, the upper portion of the shale series has a more greenish
color, and at the first and last mentioned localities this upper greenish shale
evidently lies immediately under the coarse conglomerate of these regions;
At Taggarts Ferry the bluish Aquidneck shales are exposed in the
stream bed entering the bay from the west, within a very short distance
from the shore. Overlying these shales is a variable series composed of
bluish shales, carbonaceous shales, black fine-grained sandstones, less car-
bonaceous and coarser-grained sandstones, and conglomerates with the
pebbles usually small. These occur in alternating beds, and have ah-eady
been described under the name of Sakonnet sandstones. Immediately over-
lying them is coarse conglomerate.
The dark-blue Aquidneck shales are well exposed at the Glen. South-
ward along the shore the shales are usually more black and carbonaceous.
Just before reaching Black Point an overlying series of dark shales, dark
carbonaceous fine-grained sandstones, and very small-pebbled conglomerate
comes in, representing a more northern variety of the Sakonnet sandstones.
Overlying these sandstones is the same coarse conglomerate which was
mentioned in describing the exposures at Taggarts Ferry.
East of the Sakonnet River there are no exposures of the typical
Aquidneck shale variety, but the coarse conglomerates occur, and immedi-
ately beneath the latter, according to this interpretation of the geological
364
POSITION OF SAKONNET SANDSTONES. 365
structure of this region, occur the shale, sandstone, and fine conglomerate
beds, forming the Sakonnet sandstones east of the river, from the shore
west of Windmill Hill almost as far as Browns Point. The thickness of the
sandstones along this part of the shore must amount to at least 300 feet,
but no accurate measurements were obtained.
Underlying the coarse conglomerate of High Hill Point is more sand-
stone and small-pebbled conglomerate. Immediately beneath the Fogland
Point conglomerate is greenish shale. The exposures south of Corys
Wharf, consisting of bluish shale with some sandstone, approach more
nearly to some of the Aquidneck exposures west of the Sakonnet River
than any other exposures known on the eastern side of the bay. They
undotibtedly belong beneath the coarse conglomerate, and lie at about the
same horizon as some of the Sakonnet sandstones farther southward.
Sakonnet sandstones within the Aquidneck shales, in transition to the coarse conglomerate. 1 lie
Sakonnet sandstones are here placed with the Aquidneck shales, owing to
the frequent intercalation of shales, and because the dividing line is more
readily drawn above than below the sandstones. At the same time these
sandstones, with the interbedded small-pebbled conglomerate layers, are
undoubtedly introductory to the coarse conglomerate series above.
Coarse conglomerate forming the latest Carboniferous rocks in the southern part of the Narragansett
Basin. — The various coarse conglomerate exposures mentioned form the
summit of the rocks of Carboniferous age in the localities where they are
found. Under these circumstances the temptation is very great to consider
them all as being of the same general horizon.
Purgatory conglomerate as a typical exposure. TllC pOSitioU of tllC COarSC COUgloUl-
erate at Eastons Point is perhaps the best defined. It occurs on both sides
of the anticline forming the point, and the exposures on the eastern side of
the anticline containing the famous Purgatory chasm can be readily traced
northward to the high conglomerate ridges forming the western side of the
Paradise region northwest of the reservoir. The southward pitch of this
anticline is the best assurance that this coarse conglomerate occupies a
higher position than shales of the Aquidneck series.
The upper green shales occur on Slate Hill at an elevation of 260 feet
About a mile southward they occur at a level of 180 feet. At Eastons
Point a restoration of the syncline would probably give a somewhat lower
elevation to that part of the section which most nearly corresponds to the
366 GEOLOGY OF THE NAREAGANSETT BASIN.
greenish shales northward. This apparently coi-roborates the e%'idence in
favor of a general southward pitch of the rocks in southern Aquidneck.
Owino- to the typical development of the coarse conglomerate series at
Purgatory, and its already well-known occurrence as shown by frequent
references in geological hterature, the name Purgatory conglomerate is chosen
to designate those coarse conglomerates which are supposed to belong to
the same hoi-izon.
Identity of the Purgatory and the Sakonnet River western shore coarse conglomerate i here COUid
be no closer lithological resemblance than that between the conglomer-
ates exposed between Black Point and Smiths Beach along the Sakonnet
River or East Passage and the similar beds in the Purgatory and western
Paradise regions. The lithological character of the slaty and quartzose
pebbles, the inclosed oboli,* the great size of the pebbles, the alternation
of the coarse conglomerates with sandstones, the same varieties of medium-
grained granite pebbles and the same infrequency of granite as compared
with quartzitic pebbles, and many other points easily recognized in the
field, all suggest the identity of the two series. The presence of Aquidneck
shales in the region northwest of Black Point and the eastward dip of the
coarse conglomerate suggest superposition of the coarse conglomerate upon
the Aquidneck shales.
Possible syncline between the two western Paradise ridges of conglomerate. i lie r UrgatOry
and western Paradise exposures and the Sakonnet River western shore
exposures just mentioned dip eastward. In order to place them at the same
horizon, it seems necessary to imagine at least one syncline somewhere
between the two lines of exposure. The main ridge of the Paradise region,
forming its western boundary, e^ddently dips eastward, most of the dips
being between 40° and 60°. East of the same, separated by a grassy val-
ley, is another lower conglomerate ridge, with a few verj^ steep eastward
dips, and a greater number of very steep westward dips, which can be best
summarized as steep, nearly vertical, dips. This variation of dips between
the two ridges admits of the suggestion that there is a syncline between
them. Following the strike of the nearly verticall}^ dipping ridge north-
ward, exposures with almost vertical dips soon cease. Eastward-dipping
exposures, however, continue to occur northward, suggesting that if there is
1 Charles D. Walcott, Biachiopod fauna of the quartzitic pebbles of the Carboniferous conglom-
erates of the Narragaiisett Basin, E. I. : Am. Jour. Sci., October, 1898, 3d. series, Vol. VI, p. 327.
COARSE CONGLOMERATE OF HANGING ROCKS. 367
a closely folded synclinal structure with its axis so far westward, it must be
of limited long-itudinal extent.
Hanging Rock ridge possibly the eastern side of an anticlinal fold. Tlie HaUg'ing' Rock
coarse conglomerate ridge also ag-rees, lithologically, to a remarkable degree
with the Purgatory- Paradise and the Sakonnet River western shore con-
glomerate. Its dips are verj?^ steep to the westward. If the two western
Paradise ridges were considered as forming a close syncline, the Hanging
Rock ridge could be regarded as the eastern side of an anticline lying east
of that syncline. The various exposures of conglomerate east of the Hang-
ing Rock ridge, in the woods and in the fields immediately east of the
stream, would then necessarily require interpretation as the eastern side of'
a second syncline, while the Sakonnet River western shore exposures would
in their turn form the eastern side of the next anticline. In the absence of
clear evidence on this point, the steep, nearly vertical, western dip of the
Hanging Rock ridge is almost as favorable to this interpretation as to any
other, although requiring an anticlinal fold slightly overturned toward the
east in order to make the steeply westward-dipping Hanging Rock ridge
the eastern side of an anticlinal fold.
Dips immediately east of Hanging Rock ridge. OppOSitC tllC Uliddlc leUgtll of tllC
Hanging Rock ridge a small conglomerate ridge forms a promontory pro-
jecting southward into Gardners Pond. Its dip is from 80° W. to vertical.
On the southeastern side of this promontory a more eastern exposure dips
60° E. Northward along the strike from this promontory the dip is 40° E.,
and remains east to a point east of the northern end of the Hanging Rock
ridge. An exposure east of that point dips 80° E. These dips are cer-
tainly very unfavorable to any view making the Hanging Rock ridge the
western side of a syncline and the more eastern exposures near by , in the
woods and fields, the eastern side, as suggested in the preceding paragraph.
The dips at the Hanging Rock ridge and eastward, if considered apart from
any question of correlation between the Hanging Rock conglomerate and
that along the western shore of the Sakonnet River, are certainly more
favorable to the supposition of a local anticline, and this is the view taken
by Profs. T. N. Dale, Crosby, and Barton, who visited this locality to
compare dissenting opinions.
Interpretation adopted. — Thc interpretation adopted by the writer accepts the
eastward dips of the main Purgatory-western Paradise ridge as indicative
368 GEOLOGY OF THE IS'^AEEAGAKSETT BASIN.
of its position on the western side of a syncline. It ignores the fact that
a smaller ridge immediately toward the east shows much steeper and
sometimes somewhat western dips, and suggests instead that these more
vertical dips arise in consequence of the very inflexible character of this
coarse conglomerate, even under conditions of strong folding, causing the
tilting of large masses at unusual angles. The thickness of conglomerate
forming the lower, more eastern, of these ridges is considered entirely
inadequate for correlation with the much greater mass of conglomerate
forming the larger, more western, ridge, which is so great as not to admit of
the interpretation of the lower ridge as forming a possible repetition of the
higher one, owing to the intervening' s}niclinal structure in which both are
involved.
The thickness of conglomerate forming the Hanging Rock ridge is
considered entirely inadequate for correlation with the much greater con-
glomerate section east of the ridge as opposite sides of the same anticline,
the Hanging Rock ridge forming- the western side, and the field exposures
the eastern side. Foi- this reason the Hanging Rock ridg-e is considered
the eastern side of a great syncline, with the Purgatory-Paradise lidge as
the western side. The region east of the Hanging Rock ridge is considered
as anticlinal in structure, with the Hanging Rock ridge as the western side
of the anticline and the Sakonnet River western shore conglomerate as
the eastern side. This interpretation also ignores the eastern dips of the
conglomerate exposures immediately east of the northei'n half of the Hang-
ing Rock ridge, considering these ag-ain as mere exadences of the results
possible when unusuallv hard rocks are subjected to processes of folding
in conjunction with great masses of much softer underlying- shales. This
interpretation would give approximatelv the same thickness to the coarse
conglomerates involved in the (1) two western Paradise ridges west of the
reservoir, (2) the exposures at the Hanging Rock ridge and those imme-
diately eastward, and (3) the western shore conglomerates along the
Sakonnet River.
Southward pitch of the great Paradise-Hanging Rock syncline. AcCCptlug tlfis interpreta-
tion, the Paradise region between the western Paradise ridge and the Hang-
ing Rock ridge is to be considered as a great sjmcline. The conglomerate
exposed along the roadside about a mile southwest of Black Point is con-
sidered the most northern exposure of this syncline. Its elevation is about
WESTEEN COAiiSE CONGLOMEEATE EXPOSUEES, 369
75 feet. If it lies anywhere near tlie base of the syncline the trough dips
strongly southward, since the base of the conglomerate series near the
southern end of the Paradise region must lie far below sea level. The
qiiartzitic shales forming the central parts of the Paradise-Hanging Rock
area southward are considered as pre-Carboniferous, the intercalated
igneous rocks having penetrated these shales, but not the rocks of Carbon-
iferous age.
Southward pitch of the Sakonnet River syncline. The SyncliuC bctweeU SmltllS Bcach,
Taggarts Ferry, and Black Point on the west, High Hill Point on the
north. Windmill Hill on the northeast, and an unexposed region now occu-
pied by the eastern part of the lower Sakonnet River has already been
mentioned. The shore exposures west of Windmill Hill as far as Browns
Point must once have underlain a continuation of the coarse conglomerate
series still exposed at High Hill Point and on the side of Windmill Hill, if
such a synclinal structure really exists. At High Hill Point the conglom-
erate is exposed at sea level. Southward, opposite Taggarts Ferry and
Smiths Beach, the base of the syncline must lie far below sea level, indi-
cating a southward pitch of the syncline and adding another instance of
the general southward pitching of the rocks in southern Aquidneck.
From High Hill Point to the northwestern side of Nonquit Pond, and
thence to the eastern side of Nannaquacket Pond, the coarse conglomerate
is exposed at about sea level and rises to about 80 feet above. The Fog-
land Point conglomerate is also at about sea level. The syncline probably
does not extend far north of High Hill Point.
WESTERN COARSE CONGLOMERATE EXPOSURES.
Lithologically the coarse conglomerates of Miantonomy Hill and
Coasters Harbor Island present all the features of the Purgatory coi.l-
glomerates on the east, excepting the marked elongation of the pebbles.
Since the elongation of the pebbles, wherever it occurs, is a secondary
feature, it need not be taken into account.
Possible syncline immediately west of Miantonomy Hill. At MiaUtOUOmy Hill thc COarSC
conglomerate pitches southward at an angle of perhaps 15°, conglomerate
occurring again at a lower level an eighth of a mile south of the summit
of that hill. On Beacon Hill, immediately northward, a conglomerate is
exposed, with pebbles usually not exceeding 8 inches in length. The over-
MON xxxiii 24
370 GEOLOGY OF THE NARRAGANSETT BASIN.
lying sandstone indicates also a southward pitch, and a westward dip on
the western side of Beacon Hill. In a field west of Miantonomy Hill, near
the railroad, coarse conglomerate dips 45° E., suggesting a S3^nclinal
structure between the conglomerate exposed in the field and that on the
hill. This interpretation would demand an anticlinal structure west of the
first-named exposure, a synclinal structure coming in again at Coddington
Point and Coasters Harbor Island, where coarse conglomerate again
appears, that of Coasters Harbor Island bearing the closest resemblance to
that on Miantonomy Hill.
This interpretation of the geological structure is again very free, and
is based upon two assumptions : That the conglomerate exposures on
Miantonomy Hill and those at Coasters Harbor Island, lithologically alike,
are also stratigraphically identical, and that the field exposures of con-
glomerate which dip eastward possibly belong to the same horizon.
Possibility of two horizons of conglomerate at Miantonomy Hill. Why, hoWCVCr, should
there not be two horizons of conglomerate, the exposures west of Mianto-
nomy Hill underlying the coarse conglomerate forming the summit of that
hiir? The occurrence of coarse conglomerate low down in the Aquidneck
series — in fact, according to our interpretation, at its base, in the western
part of Bristol Neck — shows the possibility of coarse conglomerate lower
than that which forms the summit of the rock of Carboniferous age in the
Narragansett Basin. Possibly this exposure west of the hill is such a lower
horizon, although not near the base of the shale series.
On the western side of the stream entering Eastons Pond from the
north, in the fields north of the first east-west road, is a conglomerate
exposure apparently dipping very low to the westward, so that the dip
would evidently carry also this conglomerate beneath the conglomerate
forming the summit of Miantonomy Hill. The exposure of conglomerate
north of Eastons Pond might therefore correspond to the section west of
Miantonomy Hill, the two forming a lower horizon of conglomerate, while
the Miantonomy Hill exposure formed the upper horizon. To wliich of
these two horizons would the Coasters Harbor Island conglomerate
belong? The writer interprets it as corresponding to the Purgatory
conglomerate. Its resemblance to the conglomerate near the summit of
Miantonomy Hill is so great as to be considered conclusive of identity,
notwithstanding the fact that conglomerates corresponding to these expo-
GEOLOGICAL POSITION OF NEWPORT (JLIFF CONGLOMEKATES. 37 i
sures do not occur at intermediate localities. The absence of these con-
glomerates at Coddington Point is also puzzling.
Interpretation adopted. — So moderate a thickucss of coarse conglomerate is
exposed in the fields northwest of Eastons Pond and west of Miantonomy
that it is impossible confidently to identify them with the much thicker
Purgatory conglomerate. The Miantonomy Hill and Coasters Harbor
Island exposures, on the contrary, suggest a much thicker section than
the field localities, and show pebbles of a size more nearl}^ corresponding
with that of the coarse Purgatory conglomerate. For this reason the writer
considers the Miantonomy Hill exjiosure equivalent to the Pin-gatory con-
glomerate, the Coasters Harbor Island conglomerate being referred to the
same horizon. Whether the field exposures are to be considered as belonging
to the same general horizon or not is left, for the present, an open question.
Geological position of the Newport Cliff section. Tho gCological pOSitioU of the
Newport Cliff" exposm-es presents another important question, to which an
uncertain answer must be returned. The conglomerate on Miantonomy
Hill pitches southward about 15°. If it has any representative southward
which is actually exposed, it is almost certainly the upper part of the New-
port Cliff" section, toward Ochre Point. Here conglomerate occurs in layers
which are interbedded with a greater percentage of sandstone and shale
than is found in the Purgatory-Paradise or in the Black Point-Smiths
Beach coarse conglomerate sections. The pebbles, moreover, are commonly
not so large, although several layers with fairly large pebbles occur, and
locally some very large pebbles are found, a few exceeding 15 inches in
diameter. Some of the largest pebbles may be seen west of Oclire Point
in a very thin conglomerate layer, at the top of the conglomerate series.
The sandstones and shales interbedded with these coarser conglomerates are
more frequently greenish and brownish than similar rocks farther down in
the cliff section.
If the upper and coarser conglomerate beds of the New^^ort Clitf sec-
tion be considered the equivalent stratigraphically of the Miantonomy
Hill section, the lower part of the Newport Cliff" section at once demands
attention on account of its peculiar lithological characteristics. This part
of the section also contains frequent conglomei-ate lavers, although the
pebbles are rather small or of only medium size. The interbedded sand-
stones are often darkened by the presence of carbonaceous matter, and the
372 GEOLOGY OF THE FAEEAGANSETT BASIlSf.
shales are frequently carbonaceous or coaly. Exposures beneath the
Miantonomy Hill conglomerate are few and do not resemble very closely
the lower part of the Newport Cliff section. There is no probability of
a considerable amount of mediiim-pebbled conglomerate underlying the
coarser bed at Miantonomy Hill, so that the Newport Cliff section appears
very much richer in conglomerate layers in that part of the section which
immediately underlies the coarser conglomerates.
If the coarse conglomerates of the Newport Cliff section be compared
with the Purgatory conglomerate, then the underlying medium-pebbled
conglomerates toward the "Forty Steps" and the western end of Eastons
Beach must correspond to the medium-pebbled conglomerate laj^ers of
much smaller thickness beneath the Purgatory conglomerate at Eastons
Point. In other words, the Sakonnet sandstones of Black Point, along the
Sakonnet River, wou.ld be represented at (1) Eastons Point by a few con-
glomerate layers with medium-sized pebbles scattered rather irregularly
among the much more abundant shales and sandstones, and at (2) the Newport
Cliffs by a greater quantity of conglomerate in a section of greater thickness.
The real difficulty in the way of a satisfactory interpretation of the
geological position of the Newport Cliff exposures is the paucity of outcrops
between these cliffs and Miantonomy Hill, or between the cliffs and Eastons
Point. Too little is also known of the rocks underlying Newport. It may
be that others, who resided in Newport at the time the various sewers were
constructed, have the necessary information, but all that the writer could
leam was insufficient to determine the correlation of the beds. The
writer's experience is that isolated exposures of small area are very unsafe
for the determination of horizons where the lithological character of the
rocks change so often as they do, for instance, at the Newport Cliffs. Con-
tinuous sections are needed. Until further evidence is secured the writer
prefers to consider the Newport Cliff section the equivalent of the Mian--
tonomy Hill and the Eastons Point sections in the sense described above.
Prof. T. Nelson Dale mentions that coal seams were struck in digging-
wells under the city of Newport. Coal seams formerly outcropped near
Sheep Point, on the cliffs. Coal plants have been found near the corner of
Marlborough and Farewell streets.^ In his published sections he places coaly
• In a sewer tunnel made nearly ten years ago, between Bellevue avenue and the first avenue
parallel to it on the east, and not far north of Ochre Point, Carbonaceous shale formed the rock
exposure. It was examined by Professor Dale.
COARSE CONGLOMERATE OF NORTHERN AQUIDNECK. 3Y8
shales beneath the city of Newport. The contact with the top of the coarse
conglomerate is unconformable. Coaly shales of considerable extent are,
however, suggestive of Aquidneck shales, since these are the only shales
having any great distribution over wide areas. This would place the rocks
beneath the city of Newport in the Aquidneck series and beneath the cliff
exposure. Either a fault or a close overturned synclinal fold must be
hypothesized to account for the present position of these rocks.^ Professor
Dale notes the presence of slates and conglomerates at Emmanuel Chapel, at
the corner of Spring and Perry streets. Conglomerates occur in Morton Park.
Portsmouth synclinal conglomerate. Near the SUmmlt of tllO PortSmOUtll S}T1-
cline the upper green shales begin to contain sandstone and some small-
pebbled conglomerate layers, overlain at various localities, it seems, by
sandstone and coarse conglomerate. Coarse conglomerate occurs, for
instance a third of a mile south of Butts Hill, in the Portsmouth camp-
meeting grounds north of Qtiaker Hill, and on the east side of the Newport-
Bristol Ferry road, half a mile west of Quaker Hill. This conglomerate,
associated with much sandstone, is believed to have been introductorv to
the coarse conglomerate series, which once must have lain above it.
East of the Portsmouth syncline there must have been an anticline
(merging southward perhaps into a monocline), in order to enable the
coarse conglomerate to appear at sea level on the eastern side of the Sakon-
net River from Fogland Point to the eastern side of Nannaquacket Pond.
Conglomerates of Warren Neck and Swansea. Tho COarSO COUglomCrate eXpOSUreS
from the western side of Warren Neck to Coles Station, along both banks
of Lees River north of the southern road to Fall River, and thence north-
ward to Swansea village, as well as the exposures found north of the west-
ern Warren Neck exposures, at Luthers Corner and in western Swansea,
are all considered as corresponding to the coarse conglomerate series lying
to the southward.
Thickness of the coarse conglomerate. — The tluckuess of the coarse couglomcrato
in the Black Point-Taggarts Ferry section was estimated to be at least 380
feet. This may not include the entire section, a part of the conglomerate
1 Prof. T. Nelson Dale, in his paper ou the Geology of the Month of Narragansett Bay (Proo.
Newport Nat. Hist. Soc, Document 3, pp. 6-14, Newport, E. I., 1885), gives a somewhat different
interpretation of the general section of this part of the basin from that presented by Dr. Foerste.
The most notable dift'erence concerns the position of the quartzite conglomerate, which Dale places
below the coal-bearing portion of the section. — N. S. S.
874 GEOLOGY OF THE NAERAGANSETT BASIN.
being possibly not exposed. Tlie Purgatory-Paradise section of coarse con-
glomerate may range between 600 and 450 feet in thickness, according as the
lower and eastern one of the two ridges is or is not included in the section.
Fossil localities. — Fcms are found in Woods Castle, in a coaly shale which
belongs stratigraphically within the coarse conglomerate series. They
occur also in the Newport Cliffs a short distance south of Marys Seat, in a
coaly black shale about 14 feet thick, overlying a conglomerate bed about
11 feet thick, with pebbles often 4 inches thick. Fossil ferns are still more
common in the coaly shales southwest of Oclu"e Point, near the top of the
sea wall. The position of these coaly shales is not accurately known.
They lie west of the Newport Cliff section with its conglomerates, but may
belong to the shale series exposed beneath Newport. This, according to
the writer's interpretation, would place them below the coarse conglomerate.
CHAPTER X.
THE ARKOSES AND BASAL CONGLOMERATES.
]S"ATICK ARKOSE.
From Natick to Cranston. — Aloiig the steop luU facG from Natick, Rliocle Island,
for 2^ miles northward into Cranston, extend the arkoses and qnartzite con-
glomerates that form the lowest rocks of Carboniferous age on the western
side of Narragansett Basin. The eastward dip of these rocks shows their
position beneath the Kingstown series, which lie farther eastward. Near
the fork of the road, half a mile northwest of Natick, a coaly black shale
overlies the arkose and is itself overlain by a qtiartzitic sandstone contain-
ing large quartzite pebbles. The arkose consists largely of detrital quartz
derived from decayed granite, and is usually found near those localities
where the immediately underlying pre-Cai'boniferous rocks consist chiefly
of granite. The quartzite conglomerate is usually found near pre-Carbon-
iferous quartzite beds, and near contact with the latter the round pebbles
give way in places to those of such angular contours as to warrant giving
the name of breccias to the lowest layers. This is es2Decially true of the
exposiu-es at Alexander McTeer's house, north of Natick. Granite pebbles
are rare, owing to lack of firmness on the part of the g'ranite in the original
ledges at the time the arkose was formed. Of course the arkose forms a
part of the detrital material between the pebbles of the coarse conglom-
erates, and quartzite pebbles are not rare in some of the beds of arkose.
In some cases the basal arkoses and quartzitic conglomerates do not exceed
100 feet in thickness, and a thickness of 200 feet seems not to be attained
in any single set of exposures. Some of the pebbles in these basal con-
glomerates are 15 inches in length.
Northward, in the southern part of the field studied by Mr. Wood-
worth, the basal arkoses and C(5nglomerates do not long continue to be
exposed, although the steep escarpment still outlines approximately the
position of these basal deposits.
The basal arkose and conglomerate beds along the western border of
the Carboniferous basin are believed to represent the oldest Carboniferous
rocks in the areas bordering Narragansett Bay. They are not a formation
376 GEOLOGY OF THE NAREAGANSETT BASIK
distinct from the Kingstown series, but represent the lowest beds of the
Kingstown sandstones and shales. The detrital material of which they
ai'e composed is evidence of the fact that areas of granite lay sufficiently
near to provide the quartz and cementing material of the arkose. The
angular breccia conglomerate at places north of Natick suggests that both
granite and quartzite existed at no great distance from the present location
of these beds. If this surmise be correct, we have a right to assume the
existence of land areas somewhere in this region. This does not demand
that the present granite and quartzite escarpment should have been a shore
line at the time the Carboniferous deposits of the Narragansett Basin were
formed. It is not probable that the land areas of that time were bordered
by such straight and abrupt escarpments.
The present granite and quartzite escarpments had probably the fol-
lowing history: Before the deposition of the Carboniferous deposits a
widely extended area of granite, quartzites, and pre-Carboniferous shales
formed the iioor of the basin. Part of this floor was above water level,
and furnished materials for arkose and conglomerates. The lowering of
the basin and the progressive overlapping of later deposits may have
entirely covered up these land areas and cai'ried the shore line much farther
westward. The direction and location of these early shore lines are in
reality not known. Subsequent to the deposition of the Carboniferous
the rocks of the entire basin were subjected to strong folding, the axes of
the folds running north-south. The granite and quartzite escarpment on the
western side of the bay represents the bed of the Carboniferous deposits,
brought up on the western side of a great synclinal fold. The escarpment
is due to subsequent erosion.
Base of the Carboniferous south of Natick. A mile SOUtll of DavisviUe, aloUg the
railroad, an abundant supply of conglomerate is to be referred rather to
the base of the Kingstown series than to the basal beds above mentioned.
From Natick to East Greenwich and Wickford Junction the steep escarp-
ment continues to indicate approximately the horizon along which the basal
deposits occur, but no exposures are found.
South of Wickford Junction it is impossible to identify the basal
deposits of the Carboniferous series. It is possible that they are not exposed.
Probable relations between the various granites and pegmatites and the Carboniferous beds. 1 [iQ
writer is inclined to favor the view that the Carboniferous series once
ARKOSE OF WESTERN BORDER OF BASIN. 377
extended from the shore exposures near Saunderstown and the Bonnet over
unbroken areas as far west at least as McSparran and Tower hills, and
covered even Boston and Little necks as far south as Nan-agansett Pier.
The basal Carboniferous of these regions probably rested upon an extensive
pre-Carboniferous granite area. In consequence of folding, the pre-Carbon-
iferous granite was raised toward the west of the Tower and McSparran
escarpments and along the area now occupied by Little and Boston necks,
while the Carboniferous was lowered into a synclinal tract lying between
these two regions along the Cove and the Pattaquamscott, and was by
later denudation severed from the Carboniferous east of Boston Neck.
There is undoubted evidence of faulting in the Carboniferous area
east of Boston Neck. The temptation is ver}^ great to account for the
alternation of granite and Carboniferous rock, in part at least, by faulting.
Some of the occurrences of detrital, presumably Carboniferous, masses m
the granite areas, however — for instance, those at Narragansett Pier and at
Clump Rocks light-house — could be explained as cases of Carboniferous
rocks once overlying the granites, but subsequently broken up and folded
in with the granites, or faulted down into them by later disturbances, only
remnants of the Carboniferous rocks remaining, owing to denudation. Or
else they must be considered as fragments of Carboniferous rocks caught
up by post-Carboniferous granites. Unfortunately, post-Carboniferous
granites are not known anywhere in the field here investigated.
Where the Carboniferous rocks are traversed by dike-like rocks, the
latter on closer examination almost invariably tiu-n out to be pegmatitic in
structure, so that the pegmatites are, as a rule, readily identified as post-
Carboniferous. These coarse pegmatites traverse the Carboniferous rocks
rather frequently south of Hazzard's quarry and Saunderstown as far as the
region northwest of the cove, and are especially well exposed at Watsons
Pier (PL XXV; see also Pis. XVIII and XIX, pp. 242, 244). But the
mass of pegmatite southwest of Wesqxiage Pond, on the hill, seems to
belong to the Boston Neck series of exposures, and appears to connect
with pre-Carboniferous granites as though the latter were in reality post-
Carboniferous. The conditions are perplexing and require more study. It
may be that careful observations might lead to more definite results, but
to the writer conclusive data seem to be lacking, although he considers the
general mass of g-ranites as pre-Carboniferous.
378 GEOLOGY OF TPIE NAREAGANSETT BASIK
The question suggests itself whether Indian Run represents another
synchne within the granite area which contains Carboniferous rocks. This
area has not been carefully investigated. The writer is inclined to consider
McSparran and Tower hills as marking the most western exposures of
Carboniferous rocks in the basin, without any attempt to assert, however,
that in times preceding the folding and subsequent denudation the Car-
boniferous rocks could not have extended farther westward. If it be
remembered that the Carboniferous deposits half a mile south of Bridge-
town and along southern Tower Hill owe their high inclination to folding,
it will be seen from a restoration of these beds to their original horizontal
attitudes that Carboniferous beds must have once extended farther west-
ward, making the western shore line pass west of Tower Hill; how much
farther west is not known.
TIVEKTOX ARKOSE.
From Steep Brook to Nannaquacket Pond. — Aloug the pre-Carbouiferous escarpmcut
extending from Steep Brook to Tiverton Four Corners a number of expo-
sures of arkose occur. Since this escarpment consists almost entirely of
granite, any overlying basal Carboniferous rocks are apt to include arkose
beds. The latter were formerly well exposed at Steep Brook, but this is no
longer the case. A fine exposure occurs in Fall River, another at Town-
send Hill in the northwestern end of the town of Tiverton, one at the
quarry northeast of Tiverton railroad bridge, and there are several expo-
sures along the escarpment east of Nannaquacket Pond in Tiverton. In
all of these localities carbonaceous shales are more or less intimately asso-
ciated with the arkoses. At Steep Brook and Fall River these were fern
bearing. East of Nannaquacket Pond and at Fall River the arkoses and
coaly shales alternate repeatedly. At Steep Brook and the quarry northeast
of the Tiverton railroad bridge conglomerate beds occur in close connection
with the arkose series. The fact that these conglomerates contain quartzite
pebbles similar to those in the Natick conglomerates and that the pebbles
in places attain a length of 6 inches does not simplify the problem, since
pre-Carboniferous quartzites are practically unknown on the eastern side of
the basin. The pre-Carboniferous quartzites on the eastern side of the
basin may have been removed by subsequent erosion, but there is no good
reason for assuming their former existence here. The thickness of the
Tiverton arkose series is usually less than 100 feet and is nowhere known
to exceed 200 feet.
SAOHUEST ARKOSE. 379
South of Nannaquacket Pond. — Tlie stecp escarpmeiit soutlieast of Nannaquacket
Pond locates approximately the line along which the arkose beds may
occur farther soiithward.
Equivalence of the Tiverton arkoses to [those near Natick. The COarSC COnglomerateS
assigned to the top of the Carboniferous series on the eastern side of the
basin overlie these arkoses within such a limited distance that it seems
hardly credible to sujopose that if the coarse conglomerates along the
Sakonnet River correspond to the Purgatory conglomerates the arkoses on
the eastern side of the basin may correspond to the Natick arkoses and
conglomerates. Yet something of this relationship must be assumed, with
the jiossibility, however, of considering the Tiverton arkoses perhaps not
so old as those occurring on the western side of the bay, their basal posi-
tion not certifying to absolute equality of age with the Natick exposures,
but only to their early deposition as compared with other deposits on the
eastern side of the Carboniferous field. For the present, faulting is assumed
to account, in part, for the remarkably short distance intervening' between
the coarse so-called Purgatory conglomerate in these regions and the basal
Tiverton arkoses, but the absence of the Kingstown series would also partly
explain the facts. The escarpment from Steep Brook to Tiverton and
thence east of Nannaquacket Pond indicates that the eastern floor of the
basin, upon which the Carboniferous rocks were deposited, consisted largely
of granitic rocks. Subsequent folding Las placed them upon the eastern
side of a great synclinal fold, and subsequent denudation has left behind the
present escarpment. The original contours of the Carboniferous basin are
unknown.
SACHUBST ARKOSE.
The western and southern shores of Sachuest Neck, the northern shore
at Flint Point, and a small exposure ofiPshore at a headland a quarter of a
mile south of Flint Point consist of arkose with which more or less coaly
shale is interbedded. Lithologically it strongly resembles the exposures
east of Nannaquacket Pond, and it contains ferns in the shale beds, as was
also the case at Fall River and Steep Brook. If the writer's view as to the
geology of this region is correct, the arkose of Sachuest Neck rests upon
Cambrian conglomerate and shale, and derived its materials from jjre-
Carboniferous granite. The total thickness of these arkose beds may
amount to 20i) feet.
380 GEOLOGY OF THE NAREAGANSETT BASIN.
CONAlSriCUT ARKOSE.
On the eastern side of Mackerel Cove arkose is found exposed north
of the granite area. It is evidently composed of the detrital material
derived from the granite, and the latter is considered pre-Carboniferous.
The statement that the arkose underlies the green shale is an assump-
tion. The thin arkose layers in the black shale at Beaver Head should be
noted in this connection, since they evidently occur at the base of the
Aquidneck shale series. Possibly the Mackerel Cove arkose is also con-
temporaneous with part of the Aquidneck shales.
ROSE ISLAND AND COASTERS HARBOR ISLAND ARKOSE.
Arkose and black shale occur on Rose Island and at the southern end
of Coasters Harbor Island. The writer has felt strongly inclined to consider
the arkose exposed on Conaniciit and on the islands last mentioned as
deposits formed in the proximity of a great pre-Carboniferous- granite area,
without any attempt to closely synchronize the various exposures. Thus,
the arkose at the southern end of Coasters Harbor Island may belong, as
far as relative age is concerned, higher in the Carboniferous series than
the arkose- on Conanicut Island. The fact that it appears so close to the
coarse conglomerate on Coasters Harbor Island suggests tlois. But this is
another point which must be left doubtful.
If the green and purple shales of the Newport Harbor Islands, of New-
port Neck, and of Sachuest Neck are of Cambrian age, as suggested, these
shales, together with the granite, probably formed exposed land areas in
the near vicinity in early Carboniferous times. The progressive overlap-
ping of Carboniferous deposits caused arkose beds to be formed, resting
upon the lowered Cambrian formations. This would account for the close
geographical association between arkose and green shale or other pre-
Carboniferous rocks in these areas. Faulting has obscured this relation.-'
Arkose is also found west of Ochre Point, east of Newport. Perhaps
in all of the cases here cited, from Conanicut, Rose Island, Coasters Harbor
Island, and west of Ochre Point, the arkose is to be considered as contem-
poraneous with some part of the Aquidneck shale series.
The arkose on Conanicut maj reach a thickness of 100 feet. The
deposits on Rose Island and Coasters Harbor Island are much less thick.
' T N. Dale, Am. Jour. Sci., 3d series, Vol. XXVII, pp. 217-228, 282-289, map, 1884.
CHAPTER XI.
THE PRE-CARBONIFEROUS ROCKS.
The pre-Carboniferous rocks of the basiu usuall}' consist of granite,
often rendered gneissoid by shearing. In a number of locahties undoubted
clastic rocks appear. This is true, for instance, of the western tliird of
Newport Neck, from Brentons Point to Brentons Cove, of all of the New-
port Harbor Islands, and of some of the shore exposures along the southern
margin of the harbor. The shales here are often purplish and sometimes
contain thin layers of limestone. At various points along the southern
Newport Harbor region rather thick layers of limestone occur, in striking
contrast to the absence of limestones in the Carboniferous series.^ The
purplish or greenish shales are frequently interbedded with a more quartz-
itic greenish or whitish rock, sometimes shaly, but usually more like argillite.
Similar rocks are found along the eastern shore of Sakonnet River
from Browns Point to the granite area a mile north of Sakonnet Breakwater.
The same purplish-colored shales, with occasional very thin limestone
layers, and the same greenish argillitic or quartzitic rocks are seen here.
The purplish shales, with their thin interbedded limestones just men-
tioned, remind the observer of the Olenellus Cambrian rocks found in
eastern Massachusetts. While not identifying these more southern expo-
sures with the same precise horizon northward, the writer is of the opinion
that eventually the purple shales of Newport Neck and Little Compton may
prove to be Cambrian rocks.
Farther inland, eastward, the exposures consist of rock varying between
quartzite and argillite, with abundant parallel shearing planes, often show-
ing the effects of subseqiient folding. The Cambrian beds in Little Comp-
ton, east of the shore exposiu'es, are often decidedly quartzitic. So are
also some of the shore exposures. It is not unlikely that these exposures
include more than one horizon, paleontologically considered.
' Prof. T. N. Dale saw, April 25, 1883, iu the possession of Mr. Coggeshall, a blacksmith at New-
port, carbonaceous shales with fragments of 10 specimens of Aviculopecteu, said to have come from
Portsmouth mine. Sketches of these fossils were submitted to Professor Von Zittel. Their impor-
tance lies in the fact that, if authentic, they are the first known evidence favoring the presence of
salt water during Carboniferous times in New England.
".S
382 GEOLOGY OF THE NARRAGANSETT BASIN.
The wliitisli rocks between the conglomerate ranges in the great
Paradise-Hanging Rock syncline resemble strongly the more quartzitic
exposures away from the shore, east of the Sakonnet River.
Quartzites occur well exposed (1) west of Natick, (2) along a road a
short distance east of Natick, (3) southwest of the town, (4) along the
northern side of Bald Hill, (5) on a knoll directly east of that hill, and
elsewhere. Possibly various exposures west of East Greenwich, east of
Nonquit Pond, and in the neighborhood of Tiverton belong here. The
quartzites west of Natick have furnished the pebbles in the basal conglom-
erate of the Carboniferous. Pebbles of similar character occur also in all
the overlying conglomerates as far up as the Dighton conglomerate.
In the quartzite pebbles of (1) the conglomerate between the Saun-
derstown sandstone series and (2) of the Aquidneck shale series on the
western side of Prudence Island fossil oboli occur.^ They are found also
(3) in the conglomerates along Newport Cliffs, and (4) in the coarse
conglomerates at Eastons Point, (5) in the Paradise ridges, (6) along the
western shore exposures of the Sakonnet River, and also (7) east of that
river north of Tiverton Four Corners. These oboli appear identical with
fossils from the passage beds between the Cambrian and Lower Ordovician
of Great Belle Island of Newfoundland. Hence they are either of late
Cambrian or early Lower Ordovician age. Notwithstanding the great
abundance of quartz pebbles with oboli, however, the quartzite containing
oboli has never been found in situ. It may be that the Natick quartzite is
a remnant of the old Cambrian quartzite, but since it contains no oboli this
can not be determined.^
Considering the great abundance of quartzite material in the coarse
Purgatory conglomerates, the quartzite miist have once occurred in consid-
erable thickness over wide areas. It is not improbable that the quartzite
once occupied a considerable part of the area now occupied by pre-
Carboniferous granite. Subsequent erosion appears, however, to have
effectually denuded these areas of the quartzite beds, excejjting in isolated
localities, as at Natick. If the pebbles were derived from large exposures
' The following species have so far been discovered in the quartzite pebbles derived from south-
eastern Rhode Island and Massachusetts; Oholus (Linguloholus) affinis, 0. (L.) spissus, and Oholus
{Lingulella) rogersi.
-Charles D. Walcott, Brachiopod fauna of the quartzitic pebbles of the Carboniferous conglom-
erate of the Narragansett Basin, R. I. : Am. Jour. Sci., October, 1898, 3d series, A''ol. VI, p. 327.
LITTLE OOMPTON AND NEWPORT NECK SHALES. 383
of quartzite lying- as far north as Newfoundland and carried southward by
glaciers, the absence of other pre-Carboniferous rocks among the pebbles is
striking.
LITTLE COMPTON AXD ISTEWPORT ISTECK SHALES.
The distribution and general characteristics of the shales in western
Little Compton and along the western shore of Newport Neck have already
been sufficiently described in Chapters V and VI, pages 281 and 316.
The shales in question are closely related lithologically, and are evidently
not similar to any kuown Carboniferous deposits of the basin. The charac-
teristic feature is evidently the presence of thin layers of dolomitic limestone
in both areas, and the presence at various points along southern Newport
Harbor of quite thick beds of a white limestone, weathering to brown. The
limestone suggests a marine origin for these shales, while the Carboniferous
of the basin is evidently a fresh-water deposit. Not a single marine fossil
has so far been found in the Carboniferous rocks, and no trace of limestone
beds has been discovered in them. (See footnote on page 381.) Under
these circumstances the Little Compton shales and the Newport Neck sliales
must evidently be consigned to some other geological horizon. The only
other horizons so far determined by fossils in eastern Massachusetts are the
Olenellus and Paradoxides Cambrian and the Carboniferous. The Para-
doxides Cambrian has so far not shown the presence of limestone beds,
nor are the shales ever reddish. The Olenellus Cambrian shales are, how-
ever, often reddish, often include very thin limestone beds, and at all the
localities named include also limestone beds 6 to 8 inches in thickness.
This suggests the possibility of the Little Compton and Newport Neck
shales being of Olenellus Cambrian, or at least of Cambrian age. Of
coiu'se, the finding of fossils will afford the only certain means for iden-
tifying the horizons of these beds.
QTJARTZITES OF KATICK.
The quartzite on the northern side of Bald Hill, along the escarpment
northwest, west, and southwest of Natick, and at various points along tlie
road between Drum Rock Hill and Natick, has already been described in
connection with the general geology of the southern part of the Carbon-
iferous basin. These quartzites are, however, pre-Carboniferous. The
same may be said also of the quartzites occurring from Natick northward
384 GEOLOGY OF THE NAREAGANSETT BASIN.
along various parts of the escarpment and thence up the Blackstone Valley
as far as Ashton and Manville.
The question as to the geological position of these quartzites is very
important, but at present is without a solution. On lithological grounds
alone they might be considered of Cambrian age, but there is little real
basis for such a determination. Perhaps the best reason so far known for
considering these quartzites as of Cambrian age is the abundant occurrence
of Cambrian quartzite pebbles in the Carboniferous conglomerates of the
Narragansett Basin. Quartzite pebbles occur at all horizons, from the con-
glomerate beds just overlying the basal arkoses to the uppermost layers of
the coarse Purgatory conglomerate. The lowest horizon at which these
quartzite pebbles contain fossil oboh, however, seems so far to be in the
conglomerate beds between the Saunderstown sandstone and Aquidneck
shale series on the western side of Prudence, and with less certainty on the
western side of Bristol Neck and northwest of Riverside. They occur in
far greater abundance in the coarse Purgatory conglomerate, being com-
monly found in any considerable exposure where long-continued search
has been made for the entire length of Aquidneck Island and the eastern
shore of the Sakonnet River. They occur again in the corresponding
coarse conglomerate at Dighton, and southwestward.
A few of the localities where quartzite pebbles with fossil oboli
have been found in situ have been indicated on the accompanjnng geo-
logical map. These fossil oboli belong probably to some late Cambrian
horizon. Hence the quartzite deposits elsewhere in the basin, especially
those near Natick, in which we are most interested, may also be of late
Cambrian age.
After a careful comparison of the quartzite pebbles in the quartzites at
Natick and elsewhere, it must be admitted, however, that the lithological
resemblance is not very close. The varied coloring shown by different
fossiliferous quartzite pebbles, especially a rather common tint of faintly
dark blue, altogether fails in the quartzite exposures so far examined. The
whiter more vitreous quartzite localities, moreover, do not present the same
cleavage as the whiter fossil-containing pebbles. Furthermore, when the
considerable frequence of oboli-containing pebbles is considered, it is rather
perplexing to find the quartzite localities in question apparently without
fossils.
QUARTZITE PEBBLES WITH OBOLI. 385
While, therefore, the suggestion that the pre-Carboniferous pebbles
may be of late Cambrian age seems to be the only one possible at present,
the very slender basis upon which this suggestion rests should not be left
out of view.^
' The origin of these fossiliferons quartzite pebbles, as well as the question of their age, has been
discussed by Mr Wood worth in his part of this monograph. It seems from Dr. Foerste's presentation
of the matter that no considerable importance can be attached to the suggestion that these pebbles
are derived from the Natick or other known quartzites which occur in the basin. — N. S. S.
MON XXXIII 25
CHAPTER XII.
THE CAMBRIAN STRATA OF THE ATTLEBORO DISTRICT.
Among the most interesting results of the examination of the geology
of the Narragansett Basin has been the discovery of a number of small
Olenellus Cambrian exposures. The first of these, locality 1, directly east
of Hoppin Hill (PL XXVI), and a mile southwest of North Attleboro, was
discovered by Prof. N. S. Shaler long before the United States Geological
Survey began its work here, but the horizon to which the fossils from this
locality belonged was not determined until the publication of Bulletin No.
30 of the United States Geological Survey, by Mr. C. D. Walcott, in 1886,
made more widely known the Olenellus Cambrian fauna of this coiTntry.
At locality 1 were found Hyolithes princepsf and HyolitheUiis micansf
in considerable abundance ; a small form of Stenotlieca nigosa was fairly
common, and a species described later as Salterella curvata was also numer-
ous. The operculum of Hyolithellus has so far not been found, but the
general Cambrian facies of the fauna at locality 1 was readily recognized
as early as 1887. In the fall of that year the writer was sent into the field
to collect fossils, and the result was the discovery of locality 2, a third of a
m.ile north of locality 1 , which has furnished almost all of the fossils described
from the Olenellus Cambrian of Massachusetts, and of locality 3, a mile
directly west of locality 2, in the open fields west of a little stream, and at
the northern end of a long farm lane. The number of species found at
locality 3 was small, but it added to our information regarding the areal
distribution of the Olenellus Cambrian in this part of the field.
The results of these investigations were published as an appendix to a
preliminary report on the geology of the Cambrian in Bristol County,
Massachusetts, in 1888.^ In the determination of species, the figures of
Bulletin No. 30 (United States Geological Survey) were followed very
closely. When widely different forms were figured under the same species,
the description was followed as well as possible. The collections the
writer was able to examine at that time afforded but little assistance in
'Preliminary descrij)tion of North Attleboro fossils, by N. S. Shaler and August F. Foerste:
BuU. Mus. C'omp. Zool. Harvard Coll., Geol. Series, Vol. II, pp. 27-41, pis. 1-2, Oct., 1888.
U-S. GEOLOGICAL SURVEN
MONOGRAPH XXXIU. PL. XXVII
&
LEGEND
r^
Carboniferous
t^.ss. (pt/ar/z/hc sandstone
g/:sh. Green shale
r.s/j, /fe & shale
///. Hyo/if^hellus
yerf. /erhical
Cong/. Con^Jomer^te
r. /. /fed /imestone
fr/l. Tri/obifes
h, Nyolifhes
peb . PebbJes
/.noc/. Limestone: nodules
SKETCH MAP
OP
CAMBHJAN FOSSIL LO(.AJ.ITIES I AND 11
SOTTTHVVEST OK NOIv'tj{ ATTLEBORO
OAMBEIAN DISTRICT OF NORTH ATTLEBOEO. 387
the determination of species. The result was naturally a number of errors.
The worst of these was the reference of a small head of some species of
Olenellus to the genus Paradoxides. The specimen found was a cast of the
lower surface of the chitinous envelope of the head, and apparently showed
facial sutures, the nonexistence of which in the genus Olenellus was already
suspected at that time. It is now very well known that the position of
facial sutures is indicated by grooves on the lower surface of the protecting
envelope of the head (exoskeleton), a cast of which could erroneously give
the idea of a partial separation of the free cheeks at the facial suture. In
spite of this incorrect reference of the cast in question, the fauna was
recognized as being of the Olenellus Cambrian horizon.
In consequence of the discovery of an Olenellus Cambrian fauna in
the red shales and limestones southwest of North Attleboro, the red shales,
sandstones, and conglomerate farther east, and, in fact, wherever found for
miles around, were considered of Cambrian age. Owing to their general
westward dip they were even viewed as anteceding the fossiiiferous beds.
The report, however, had scarcely been pubhshed when, early in 1889, the
writer found loose bowlders of red sandstone with well-preserved specimens
of calamites in the hills southwest of the southern end of the reservoir pond
south of North Attleboro. In consequence all the red shales, sandstones,
and conglomerates just described as Cambrian, excepting the shales
occupying the valleys of localities 1, 2, and 3, were referred to the Carbon-
iferous. In the writer's thesis, On the Igneous and MetamorjDhic Rocks of
the Narragansett Basin (Harvard Univ., 1890), these red phases of the
Carboniferoiis were described as a group of the Carboniferous, the Wamsutta.
After this thesis had been presented, in the spring of 1890, Cordaites leaves
were found in sitti, west of the road, two-thirds of a mile southwest of
the reservoir pond. At a later date Mr. J. B. Woodworth discovered
abundant stems of calamites in an exposure on the north side of the road to
Attleboro Falls, about two-thirds of a mile southeast of the North Attleboro
post-office ; and finally, in 1895, the writer found a poorly preserved specimen
uf calamites in the arkose beds in the northwestern part of North Attleboro,
north of Division street ^
The result of these discoveries has been of considerable importance in
' It should be noted that in 1880 Crosby and Barton recognized the Carboniferous age of the red
beds in the Norfolk County Basin and inferred from this a similar age for the red rocks about North
Attleboro, but they did not discover the factthataportionof these beds were of Cambrian age. — N. S. S.
388 GEOLOGY OF THE NARRAGANSETT BASIN.
arriving at a correct knowledge of the litliological characteristics of the
OlenelKis Cambrian in eastern Massachusetts. Instead of being a forma-
tion in which sandstones and conglomerates form a predominating element,
the Olenellus Cambrian of eastern Massachusetts, as at present recognized,
consists chiefly of reddish and greenish shales and slates with whitish and
reddish layers and nodules of limestone. Sandstone beds are known at
almost all exposures, but form only a very unimportant element of the
Olenellus Cambrian, as far as this horizon has been definitely recognized.
Some sandstone is, for instance, found associated with the reddish
shales and limestone beds discovered in 1889 by the writer at locality 4,
just north of the State line, a short distance east of the road leading from
West Wrentham to Diamond Hill.
North of Mill Cove, in the Boston Basin, the Olenellus Cambrian
(fossils discovered by the writer in May, 1889) consists chiefly of reddish
and cherty greenish slate, including limestone nodules, and a few limestone
beds, the latter containing Hyolithes communis and Hyolitliellus micans.
At the southern end of Nahant the Olenellus Cambrian (fossils first
recognized by the writer^ in April, 1889, but previously discovered and not
identified by Prof Alfred C. Lane and J. Sears) consists of cherty greenish
slate, with two or three white limestone layers, the latter containing Hyolithes
communis and a small form of Stenotheca riigosa. Near the southwestern
angle of Topsfield similar cherty greenish slates occm-, the fossiliferous
limestone being, however, hard and light blue in color.
At Achelaus Hill, in West Newbury, Mr. John Sears reports another
instance of cherty slates similar to those at Nahant, and containing similar
fossils.
No great masses of sandstone and conglomerate have so far been
recoo-nized as belonging to the Olenellus Cambrian horizon, or as being
closely associated with the same.
CAMBRIAX BROOK LOCALITIES.
LOCALITIES 1 AND 2, SOUTHWEST OF NORTH ATTLEBORO.
A great mass of quartzite on the southeastern side of Hoppin Hill
mav belong to the Olenellus Cambrian. Fragments of reddish shale occur
in the soil farther eastward.
' See The paleontological horizon of the limestone at Nahant, Massachusetts: Proc. Boston Soc.
Nat. Hist., Vol. XXIV, 1889.
CAMBRIAN OF NORTH ATTLEBORO. 389
At localit}^ 1, just north of the road leading eastward down from
Hoppin Hill, there is a small knoll, composed chiefly of shale, more greenish
westward, where it includes a few thin white quartzite layers, strike N. 10°
E., dip 80° W.; reddish eastward, where the shale includes limestone layers,
pinkish where fresh, red where strongly weathered. (Map, PI. XXVII.)
In the limestones were found the following fossils: Stenotlieca rugosa
var. i)aupet% Pleurotomaria (Baphistoma) attlehoroensis, Fordilla troyensisf
left valve, Hyolithes princepsf H. hillingsi, HyolUliellus micansf, Salter ella
curvata. Northeast of locality 1,50 feet, are found some very small exposures
of red shale with limestone layei's, including Agraulus stremms, strike N. 10°
E., dip 70° W. Farther northward 1 00 feet, a little east of north from locality
1, is another knoll with red shale on the eastern side, containing red lime-
stone with Hyolithes and Hyolithellus. The ridge itself is composed of
greenish and reddish shales on the eastern face, and greenish shale including
thin sandstone and quartzite beds along the middle and western sides.
About 150 feet north of the last-mentioned knoll, or 340 feet north
of locality 1, reddish shale, abundantly cleaved in various directions, occurs
just west of the stream, and another exposure occurs near by on the eastern
side of the stream. West of these localities green and red shales occur,
also much cracked; 50 feet farther north, and again 110 feet farther north,
limestone bowlders occur. Another limestone bowlder is found about 50
feet west of the last-mentioned bowlder and about 525 feet a little west of
north of locality 1.
About 560 feet almost directly north of locality 1 and just south of a
small stream red shale is found including thick red limestone beds in almost
vertical position. Thirty-five feet northwest of the same red shale occurs;
50 feet directly westward occurs limestone containing Hyolithes and Hyoli-
thellus, strike N. 50° E., dip vertical.
Thirty feet northwestward is the beginning of a set of greenish shales
including numerous quartzite layers, the most eastern one 12 inches thick,
the intermediate ones a few inches in thickness, the most western layer
nearly 2 feet thick and white in color, strike N. 21° E., dip 60° E.
About 25 feet noi'theast of this most western exposure a similar thick
quartzite layer with a similar strike occurs.
About 110 feet east of the last-mentioned quartzite exposure, on the
northern side of the small stream already mentioned, a series of red shale
390 GEOLOGY OF THE NAEEAGANSETT BASIN,
ridges begins, trending N. 20° E. for a distance of 200 feet. Just north of
a wood road the shales strike N. 30° E., with a dip of 85° to vertical. The
shales contain nodules of limestone which have yielded a few casts of
Agraulus stremms.
The ridges above described terminate at a point just south of the open
fields. About 300 feet northwestward, near the western edge of the open
fields, occurs locality 2. It is a knoll trending N. 15° W. and consisting
chiefly of reddish and greenish shales ; lying upon the top and western side
of the knoll are great limestone blocks whose position in the section can
not be accurately determined, but which have furnished all the fossils cited
as coming from locality 2. The bowlders seem to belong to layers in the
immediate vicinity, but to have been broken up by the evidently strong
folding and shearing of the Cambrian strata in this region.
The following fossils have been found at locality 2: Oholella atlantica
Walcott, figured but not named in our report; Oholella crassa Hall, Scenella
reticulata Billings, Stenotheca curvirostra S. & F., Stenotlieca rugosa var.
ahrupta S. & F., Platyceras primcBvum Billings, Hyolitlies americanus, Hyoli-
tlies communis vai*. emmonsi Ford, Hyolitlies quadricostatus S. & F., Microdis-
ciis hellimarginatus S. & F., M. lohaius Hall, Olenellus iimlcotti S. & F.
(probably a young form of some known species), PtycJioparia attleboro-
ensis S. & F. (probably the young form of some species of trilobite),
Agraulus stremms f Billings.
Northwest of locality 2, on the other side of a fence, is another knoll,
trending N. 23° E., consisting chiefly of reddish and greenish shales, but
containing on the west side a few nodules of limestone which have aff'orded
Hyolithes and fragments of Agraulus.
There is a similarity of trend between the Cambrian deposits at locality
1 and immediately northward, and at the margin of the granite hill imme-
diately to the westward of it. This is also true in a measure of the outcrops
south of the stream about 500 feet north of locality 1, and 600 feet south of
locality 2, where the quartzite shale and limestone beds strike northeastward,
while the granite hill on the west seems to make a similar deflection.
Again, at locality 3 and northwestward, the Cambrian strata strike north-
westward, apparently following the general trend of the eastern margin of
the granite hill.
Quartzite occurs at the southeastern angle of Hoppin Hill, just north-
OAMBKIAN OF NOETH ATTLEBORO. 391
west of locality 1, in the underbrush, and about halfway between locali-
ties 1 and 2 on the west side of the set of exposures already described.
The temptation is very strong to consider the quartzite and the associated
green shales as forming the lowest beds of the series actually exposed.
The limestone beds immediately toward the east of the green shale and
associated quartzite layers, containing Hyolithes and Hyolithellus chiefly,
at locahty 1, and again just east of the green shales and sandstones halfway
between localities 1 and 2, could then be considered as forming an immedi-
ately overlying horizon, while the beds still farther eastward, containing
frequent trilobite remains (Agraulus strenuus), might be considered as
belonging to a still higher horizon. This would suggest that locality 2
belongs to a horizon slightly higher than locality 1.
About 700 feet north of locality 2 is found a granite boss, the northern
margin of which extends northeastward, forming a steep wall. On the
northern side of this wall, in close contact with the granite, a small exposure
of red shales was unearthed in 1887.
Red shales also occur at various points on the eastern side of the valley
in which localities 1 and 2 occur. The general conclusion is that the val-
ley as far as described is underlain altogether by Olenellus Cambrian rocks.
The western side of the valley is bordered by the HopjDin Hill granite
boss. On the northeastern side, toward North Attleboro, occurs the second
boss, already described, and along the remainder of the eastern side of the
valley the Olenellus Cambrian is overlain by the Carboniferous. The most
southern Carboniferous exposure north of the east-west Hoppin Hill road
and east of the Cambrian area, strike N. 10° W., dip vertical, occurs on
the hillside, only 325 feet north of the road leading east down from Hoppin
Hill. Another exposure is 250 feet north; a third is 115 feet north, strike
N. 40° E.; a fourth is 75 feet north, strike N. 15° E., dip steep west. All
of these exposures are conglomerates, in which the pebbles consist of a hard
glassy quartzite.
South of the Hoppin Hill road leading eastward are several additional
exposures of Carboniferous conglomerate and shale on the east side of the
Olenellus Cambrian valley.
The construction of the new railroad through the western part of the
village of North Attleboro has disclosed a series of red shales south of
the depot, as far as the bend of the road toward the southeast. The
392 GEOLOGY OF THE NAEEAGANSETT BASIN.
geological position of these shales is unknown. Next the depot and north-
ward occur exposures of arkose, undoubtedly Carboniferous. It is possible,
however, that the red shales in question still belong to the Olenellus Cam-
brian, which is here again overlain by the Carboniferous.
VALLEY OF LOCALITY 3.
The road across Hoppin Hill leads from locality 1 , first westward, then
southwest, nearly south, then again west until a small stream is crossed.
A short distance west of the stream is a house. Along the farm lane to the
northward red limestone bowlders apjDear in the fence wall on the left side of
the way. The bowlders increase in frequency as the end of the lane
is approached. At the northeastern end of the field, just west of the
northern end of the lane, red shale is exposed in the soil. The limestone
bowlders probably belong in situ somewhere among the red shales of the
vicinity, but at the present time their precise location can not be determined.
The above-mentioned limestone bowlders have furnished the following
fossils: Oholella crassa, Scenella reticulata, Stenotheca rugosa var. ahrupta,
Hyolitlies communis, possibly also H. communis var. emmonsif Microdiscus
bellomarginatus, and Agrauliis strenuus. Judging from the fauna alone, local-
ity 3 belongs to the horizon of locality 2, rather than to that of locality 1.
No quartzitic layers have been observed in this valley, and the actual expo-
sures, as already stated, are confined to red shales. The Olenellus Cambrian
deposits of this valley are bordered on the east by the granite of Hoppin
Hill. Toward the northwest occur several granite exposures, eAndently
connected beneath the soil, and trending approximately north and south.
Directly west there are no exposures, but if there be any Cambrian in this
direction it is probably ovei'lain by the Wamsutta Carboniferous, which is
known to occur considerably farther westward in the valley of Abbotts
Run. In this direction ai'kose, possibly near the base of the Carboniferous,
occurs about a mile north of locality 3, on the road from North Attleboro
to Ai'uolds Mills, and is quite abundant eastward as far as North Attleboro.
Wamsutta Carboniferous conglomerate occurs also a mile and a half south
of locality 3, apparently covering the Olenellus Cambrian in this direction.
Red shales occur at various points west and southwest of South Attleboro,
but so close to Wamsutta Carboniferous exposures that it is impossible for
the present to consider them as of Olenellus Cambrian age. It may, how-
CAMBRIAN NORTH OF DIAMOND HILL. 393
ever, be worth while to call attention to their distribution as recorded in the
section of this report which has been prepared by Mr. Woodworth.
LOCALITY 4, NORTHEAST OF DIAMOND HILL.
Along the road from Diamond Hill northward to West Wrentham
exposures of granite are met almost immediately on crossing the State
line fi-om Rhode Island into Massachusetts. After following the southern
margin of the granite hill eastward along the base of the hill for a distance
of several hundred feet, a change in direction of the border toward the
northeast takes place. Here a number of red limestone bowlders are found
on the hillside. Toward the brow of this hill there is a fair exposure of red
shales dipping at a high angle westward and striking east of north. West
of these, quartzitic beds probably occur, as is shown, by fragments in the
soil and on the hillside.
The loose bowlders on the hillside evidently are almost in situ and
contain Hyolithes princeps f and Hyolithellus micans f , siiggesting nearer rela-
tion with locality 1. From the top of this part of the hill it is a distance
of about 100 feet to the border of the granite mass forming the main body
of the hill. Along the brow of the hill westward the granite is seen to
inclose long thin layers of an argillitic purplish or brownish rock, which
may possibly be fragments of Olenellus Cambrian shale hardened by meta-
morphism. It is impossible to determine from these inclusions whether the
granite of these regions is to be considered as pre- or post-Cambrian in age.
If the fragmental inclusions referred to be Olenellus Cambrian shales the
granite must evidently be considered as post-Cambrian. Post-Cambrian
granites are well known in the Quincy region in eastern Massachusetts.
MAPS AND SECTIONS.
The uncertainty which accompanies many of the views regarding the
geological stiiicture of the lower Narragansett Basin is largely due to the
fact that the greater part of the area is covered by glacial di-ift and sand
plains or concealed by the water of the many arms of the bay. This is
well brought out by the map, which indicates the position of almost all
outcrops of any value for geological purposes. Moreover, the outcrops are
frequently scanty or absent at the very horizons where it is exceedingly
desirable to have them in order to determine the question of the succession
and the equivalence of the rocks. It was necessary on tliis account to
leave some areas without other indication than the color for the general
Carboniferous. The boundaries of some of the divisions recognized may
eventually have to be somewhat shifted, as sewers, ditches, and cellars
expose rocks now hidden from sight.
.Moreover, in order to present anything in the nature of a section
across strata, it was necessary to generalize the interpretation of outcrops.
A reference to the map will usually indicate the extent to which this has
been done.
There is perhaps little doulDt that both the Kingstown sandstones and
the Aquidneck shales have been considerably folded. Tliis must certainly
be true of the Kingstown sandstones between Wickford and Potowomut
Neck, and also of the Aquidneck shales from Coddington Cove to Black
Point. But unfortunately we have so far no indications as to the precise
locations of any of the synclines or anticlines in tliis system of folding. It
therefore seemed impossible to introduce folds into the section, offering
jjossibly a source of even greater en-or than if these indications were
omitted, but the general necessity of assuming folding was brought out
clearly in the text. Actual exposures are shown in the sections by solid
lines, while inferences as to the continuation of these exposures beneath
the soil and the probable attitude of strata where there are no exposures
are indicated by dotted lines.
U.S. GEOLOGICAL SURVE\
MONOGRAPH XXXIII. PL. XXVIII
Dips probably ht¥ e^s/ r
Th/ssechon ^ffempfs/ocorre/ste fhechiefei^oost/r^si^ffh simifar/i^ho/cg/cafcheracfen^
SECTIONS IN THE NARRAGANSETT BAY REGION
U.S-GEOLOGICAL SURVEY
MONOGRAPH XXXIII. PL. XXIX
■Si 5
? s-
- — ^^
4
1
~^
Vt;!'^^^'^^-^
l/ff/e Compfon shale
SECTIONS IN THE NARRAGANSETT BAY REGION
us. GEOLOGICAL SURVEN
MONOGRAPH X/XII
/felahonofCarbonJape^m Granifenotceriain
Purgatory coarse c
7 eha/e So -Jooft
Acjufdneck shales. 2?oo'J5oof}'
Prudence Island
Coaly Shaie Joo - ISoft Co/^/omeraie i-coalysha(e
O^ooTerate.ffeclfyf^. r
Kingstotvn sandstones HSoo feet
Basal ar/ft>s€ 5o~f5off.
"^ 1
CarSom'fierous
%
J
1
^-
1
!,} 1
iTnpinnnnnnn^nnriinTiii
"" Cambrian
^-
^i'^
-,-J.Jm,'_-', \'-
:.;.•%
„ Carboniferous
SECTIONS IN THE NARRAGANSETT BAY REGION
2
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wg
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OS
as
o =
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INDEX.
J^,
Page.
AbingtoD, Mass., fault in 129
Abington quadrangle, Coal Measure beds in 193-194
Achelaus Hill, West Newbury, Mass., Cambrian
Tocksat 388
Ackno-wledgments to coadjutors 211
Agraulus strenuus, occurrence of 389, 390, 391, 392
Alethopteris, occurrence of 181
Allegheny Mountains, age and character of 10
Almys Pond, E.. I., granite near 316
Amphibolite in dike at Lincoln, character of 108
Analyses, coals 83, 161, 191
limestone 150
Annularia, occurrence of 191,285
Annularia longifolia, occurrence of 268, 320, 321
Anthracomartus woodruffi, occurrence of 202
Appalachian Mountains, ancient mountain range
east of and parallel to 11
difference in degree of erosion in eastern and
western parts of 40-46
difference in form of folds on east and west
sides of 12-13
folds of 10-13
form and origin of basins east of 13
Aquidneck Coal Company, operations of 207
Aquidneck Island, K. I., Aquidneck shales on 252-358
coal beds of 79, 80
coal mine in 207
folds on 345
granite area on 273-274
rocks of 284-330
suggested esploration for coal on 85
Aquidneck shales, area! distribution of 361
debatable question as to inclusion of Kingstown
series in xviii-xix
equivalence of Kingstown sandstones and 361-363
folders of 394
fossils of 363
geologic equivalents of 358-359
occurrence and character of 348-363
table showing geologic place and equivalents of. . 134
thickness of 352-354, 357-358, 359
view of wave-cut bench in 352
view showing fretwork feathering of 362
Arkose, occurrence and significance of 50-55
Ashton, R. I., Cumberland quartzite at 106
Ashton schists, occurrence and character of 107
Asterophyllites, occurrence of 174, 191
Asterophyllites equisetiformis, occurrence of 168, 204
Atlantic coast, basins of sedimental depression on.. 13-15
Carboniferous basins of 38-39
character and extent of erosion on 44-46
geologic history of shore land basins of 30-36
Page.
Attleboro, Mass., analysis of limestone from 150
Carboniferous beds in 175--180
sections at and near 153, 176, 177, 182
syncline at 179-180
view of Carboniferous sandstones at 176
views of conglomerate at and near 176, 184
view of pebbles from Dighton conglomeratenear. 186
view of raindrop imprints on rocts near 178
view of ripple-marked sandstones near 178
Attleboro district, Cambrian strata and fossils of - . . 386-393
Attleboro sandstone, occurrence and character of . . . 151-152
table showiug geologic place and equivalents of. 134
Arachnida, occurrence of 202'
Archean rocks, occurrence and character of 114-118
Arkose, occurrence, character, and significance of... 50-58,
135-139, 284-286, 375-380
Arnolds Mills, R.I., granite porphyry at 117
geologic section of beds near 157
J3.
Barbers Height, E.I. , Kingstown series at 334
Barton, G. H., acknowledgments to 211
cited as to anticlinal structure of Hanging Rock
district 299
cited on .structure of Hanging Rock ridge 367
Basal conglomerates, occurrence of 375-380
Base-leveling, general cliaracter and extent of 47-49
marine actions contributory to 76
Beacon Hill, R. I., conglomerates at and near. 304, 305, 369-370
Beaver Head, R. I., rocks of 338-339
Bibliography of the Cambrian and Carboniferous
rocks 212-214
Bishop Rock, R. I., shales near 305-306
Black Point, R. I., rocks near 290-293,334
Blactstone Coal Company, operations of 206
Blackstone River, folded and faulted Carboniferous
shales on 162
Blackstone series, geologic place of g
occurrence, character, and relations of 104-109
Blake Hill, Mass. , fault block: at 180
faults near 183-184
thrust plane at 133
Blattinarise, occurrence of 203
Bogs, agricultural utilization of 78-79
Bonnet (The), R. I., Kingstown series at... 333,334,337,344
Boston Basin, Mass., geologic history of 13-15,24-25
erogenic action in 24-25
Boston Neck, R. I., faulting near 377
Kingstown series at '. 333
Bowlder clay, thickness and character of 69-70
Bowlder trains, length of 71-72
Brachiopods, Cambrian, occurrence of 109,110.111,112
395
396
Il^DEX.
Braytons Point, Mass., shales with fossil plants at. . 268
Brentons Cove, E. I., rocks near 316,317
Bridgewater, Mass., Carboniferous beds near 192-193
coal beds in 205
Bristol, E. I., coal beds at -,• 79-80,206
fossil insects from 202,201
Bristol Neck, E. I., Carboniferous and granitic rocks
on 261-263, 343-344, 351-352
synclinal fold near ^^^
Brockton, Mass., Carboniferous beds near 192-193
Browns Point, E. 1., rocks at and near 281-283,286
Burr, H. T., cited 1*''
Butts Hill, E.I., rooks at and near 327,328
C.
Calamites, occurrence of 170, 174, 191,321
Calamites suokovii, occurrence of 165
Cambrian rocks, bibliography of 212-214
map showing distribution of pebbles from 110
origin of red color of 62-63
pebbles and fossils from 109-113
Cambrian rocks and fossils, occurrence of 381,
382, 383, 384, 385, 386-393
Canton, Mass., gabbro and granitite at 118
Canton Junction, Mass., gabbro and granitite at 118
Carboniferous basin, boundary of 124-130
Cambrian and other inlying areas in 130-131
conditions of strata in 119
features of H9-132
features of faults on border of 132
maps and sections of 121, 122, 123
Carboniferous clay slate, fresh-water origin of 202
Carboniferous conglomerates, character of 64-67
glacial pebbles derived from 70-71
Carboniferous period, development of fresh-water
basins on Atlantic coast during 38-39
geologic conditions immediately preceding 8-9, 13
Carboniferous rocks, basins in 12
bibliography of 212-214
folds and fractures limited to 20-21
line of separation between preCarboniferous
Now England areas of 12
occurrence, character, and thickness of- . 119-201, 208-210
origin of red color of 62-63
original distribution in eastern Appalachian
coalfield 38-39
original extent of 40
precise age of 36-37
series underlying 104-113
table siiowing 134
Carboniferous sandstones, view of 1S6
Carrs Point, E. 1., rocks near 319
Case's coal mine, operations at 206-207
Caseys Point, E. I., Carboniferous rocks near 248
Castle Hill, E. I., rocks at 31"
Central Falls, E. I., rocks of Wamsutta group near. . 147
Chace, G. F., record of artesian well-boring furnished
by 108
Chartley quarry, section in 19*^
Chemical analyses. [See Analyses.)
Churchs Point, E. I., Carboniferous rocks near 283
Clark, E. F., fossil plants collected by 203-204
Clay, bowlder, occurrence of 69-70
Clay slate (Carboniferous), fresh-water origin of 202
Clump Eocks, Carboniferous rocks atandnear 244-245
Coal, analyses of 83,161.191
economic value of 80-88
occurrence and character of beds of 79-88,
161, 169, 171, 176, 182, 189, 190, 191, 192,
198, 205-207, 321, 322, 323, 324, 325, 372
places for exploration for 85-88
profitless exploitation of beds of xix
suggested method of prospecting for 207-208
Coal field of Eastera Appalachians, original distribu-
tion of 38-39
Coal Measures, areas, exposures, subdivisions, thick-
ness, and general features of 159-201
Coastal erosion, character and extent of 44-46
Coasters Harbor Island, arkose of 380
Carboniferous rocks ou. 306-307, 370, 371
contact line of Carboniferous and pre-Carbonifer-
ous rocks on 308-309
Cobb, Collier, cited on increase of metamorphism
with increase of depth of strata 191
cited on King Mountain, !N. C 44
record of boring at Portsmouth, E. I., examined
by ■ 321
Cochesett Station, Mass., section near 192
Cockroaches, Carboniferous, occurrence of 202
Coddington Cove, E. I., rocks near 319
Coddington Neck, K. I., shales on 305
Coloration of rocks, causes of 115
Coman, C. "W., acliuowledgments to 211
Compression of rocks by lateral strain, evidence of. 17-18
diagram showing conditions of 19
Conanicut Island, E. I., Aquidneck shales on 349
arkose of 380
Carboniferous rocks of 308, 339
folding of Kingstown series on 345
fossil plant localities on 347
geologic features of 228-235
Kingstown series on 339
probable folding in 340-341
thickness of arkose on 380
Conglomerates, occurrence and character of 55-61,
64-67, 375-380
glacial pebbles derived from 70-71
origins of 55-59
record value of 59-61
Connecticut Basin, geologic history of 13-15, 23-24
erogenic action in 23-24
Cordaites, occurrence of 170, 191.387
Corys Lane, section near 320-321
Cranston, E. I., analysis of coal from 161
bed of limestone in 108
coal beds at 79,80,206
coaly shales at 335
fossil insects from 202, 203
Kingstown series at 335-336, 342
Cranston beds, occurrence and character of 159-164
table showing geologic place and equivalents of. 134
Croll, James, cited 64
Crosby, "W. O., cited as to anticlinal structure of
Hanging Eock district 299
cited on coloration of rocks 115
cited on Montalban rocks 104
cited on structure of Hanging Eock ridge 367
features of geologic map prepared by 125
Crosby, W. O., and Barton, G. H., cited on boundary
of Carboniferous basin 125, 127
INDEX.
397
Page.
Crosby, W. 0., and Barton, G. H., cited on Carbon-
iferous age of red beds about North Attle-
boro 141,387
cited on dike rocks of Paradise liock— Hanging
Kock region 301
cited on Primordial rocks 109
Cumberland, R.I. , coal mine in 206
conglomerate beds at 140
iron ore at 89
Cumberland Hill. R. I., bowlder train at 72
Cumberland quartzites, character and occurrence of. 106-107
Current and surf action, character and extent of ero-
sion by 76
D.
Dale, T. Nelson, cited as to anticlinal structure of
Hanging Roct district 299
cited as to unconformity between Cambrian and
Carboniferous 308
cited on fern impression in shale on Conanicut
Island 339
cited on obscuration of rock relations by fault-
ing 360
cited on occurrence and position of conglomer-
ates at Newport 373
cited on occurrence of coal seams and coal plants
in excavations at Newport 372
cited on occurrence of quartz-porphyry on New-
port Neck 316
cited on possible unconformity between Carbon-
iferoxis arkose and Cambrian shale near
Sachueat Point 287
cited on rocks of Paradise Rock, Hanging Rock
region 303
cited on salt-water fossils in Carboniferous shales - 381
cited on structure of Hanging Rock ridge 367
cited on thickness of shales at Eastons Point. . . 358
early geologic map prepared by 133
fossil fern locality^ Conanicnt Island, discov-
ered by 347
Dana, J. D., cited 127
Davis, W. M., cited on formation of faults in the Con-
necticut Basin 23
Davisville, R. I., Carboniferous rocks near 251
Dedham quadrangle, Carboniferous beds of 187-193
Denudation, difficulties of stratigraphic determina-
tion occasioned by 101-102
Deposition, cycles of 49-50
Devils Foot Ledge, R. I., view showing cross stratifi-
cation in pebbly sandstone at 248
view showing sandstone-gneiss at 334
Diabase, occurrence of 152-153
relations of felsite and 154
view of dikes of 152
Diamond Hill, R. I., Cambrian rocks and fossils of . . 393
granite-porphyry and quartz at 117, 118
quartz mass at 155
Dictyopteris scbeuchzeri, occurrence of 204
Dighton conglomerate, views of 184
view of pebbles from ^, ige
Dighton conglomerate group, beds of 184-187
table showing geologic place and equivalents of. 134
Dikes and dike rocks, occurrence of 27-29, 152-153
Diorite, occurrence of 118
Distortion of pebbles and fossils by compression 18
Dodgeville, Mass., conglomerate beds near 175-176
Dumpling Rock, Conanicut Island, character of 234-235
Dutch Island, R. I., geologic features of 227-228, 337-338
E.
East Foxboro, Mass., gabbro and granititeat 118
East Greenwich, R. I., Carboniferous rocks near. 251, 252-253
East Providence, R. I., cross section near 168
Tenmile River beds at 164-165
Eastons Point, R. I., rocks at and near . 294-295, 357, 365, 372
Eastons Pond, conglomerates near 303, 370, 371
Economic resources of the basin *. 77-90
Emmons, A. B., analyses of coal cited from 191
cited on fraudulent coal core from boring made
near Lebanon Mills ' 172
cited on Rhode Island coals 83, 84, 86
Emmons, E., cited on Cambrian rocks 104, 109
Erosion, glacial, amount of 71-76
relatively rapid and etfective work of 73
Ettoblattinaclarkii, occurrence of 203
Ettoblattina exilis, occurrence of 203
Ettoblattina gorhami, occurrence of 203
Ettoblaiitina illustris, occurrence of 203
Ettoblattina reliqua, occurrence of 203
Ettoblattina scholfieldi, occurrence of 203
Ettoblattina sp., occurrence of 203
F.
Fall River, Mass., arkose deposits near 51-52
granite and Carboniferous rocks at 270
Faulting, occurrence and directions of 310, 377
Felsites, occurrence of lie, 153-155
Ferns, fossil, occurrence of 347, 363, 374, 378
Finlay, J. R., acknowledgments to 211
cited on boundary of Carboniferous basin 127
Finlay, F. H., and Richmond, H. I., cited on gabbro
hills of Sharon, Mass H8
Flint Point, R. I., arkose and shaly rocks near 283
Flora, Carboniferous 170, 181, 204
Foerste, A. F. , area surveyed by xvii
cited on quartz veins in granite-porphyry at
Diamond Hill, R. I ns
cited on Wamsutta group 141
cited on fence- wall geology 102
cited on horizon of limestone at Nahant 388
description of Cambrian deposits of the south-
western part of the basin prepared by 381, 393
description of the Carboniferous strata of the
southwestern portion of the basin prepared
by 215-380
"Wamsutta group of 141
Foerste, A. F. and Shaler, N. S., cited 109
Fogland Point, R. I., conglomerate at 278-279
Folding, age of the 22-23
types of 16-17,21-22
Folding and faulting, difficulties of stratigraphic de-
termination occasioned by 101
Folds, forms and attitudes of 16-17, 21-22
plan of 27
Foolish Hill, Foxboro, Mass., basal arkose at 135
Carboniferous strata at 188
exposure of red rocks of Wamsutta groups at . . 143, 144
fault at 128
section at 190
Fordilla troyensia, occurrence of 389
398
INDEX.
Page.
fort Adams, rocks at - 317
Fort Greene Park, rocks of 309
Forty Steps, Newport, E. I., rocks at and near. 3U-3U, 372
Fosboro, Mass., coal bed in 205
gabbro and granitite at 118
Fox Hill, Conanicut Island, R. I., geologic features
of 228-229
Franklin Society of Providence, R. I., list of Coal
Measure plants compiled by 205
records of well borings preserved by 163
Fuller, M. L., cited on Carboniferous area nortk of
Brockton 129
G-.
Gabljro, occurrence of ,- 118
Gardeners Neck, Mass., Carboniferous beds on 267-268
Gay Head, Martbas Vineyard, deposits of arkose at- 54
Geological succession of formations in tbe Basin 8-10
Gerablattina fraterna. occurrence of 203
Gerablattina scapularis, occurrence of 203
Glacial erosion, amount of 71-76
difficulties of strati graphic determination occa-
sioned by 102-103
effects and products of 64-77
relatively rapid and effective work of 73
Goat Island, R.I. , rocks of 3U9
Goat Rock Cliff, near Plainville, R. I., section at... 180-181
Goniopteris (Pecopteris) unita, occurrence of 204
Gooch, F. A., analysis of coal by 83, 161
Gould Island, R.i., rocks of 272-273,356
Granite, areas of 262-263
Granite-porphyry, areas of 117
Granitic rocks, occurrence and character of 114^-116
Granitites, occurrence, character, and age of 114-116,118
Griswold, L. S., and Marbut, C. F., cited on bound-
ary of Carboniferous Basin 127-128
Gull Rocks, R. I., shale of 307
H.
Hall, -James, orogeuic theory of 16
Halsey Farm, Silver Spring, R. I., sections at and
near 166, 167
Hamilton, R. I., Carboniferous rocks near 249, 250'
Hammond Hill, Mass., Kingstown series at 344
Hanging Rock ridge, features and structures of 367, 368
Hanging Rocks, conglomerates of 298-300
pre-Carboniferous area near 300-303
Hanover, Mass., Carboniferous sandstone rock at . . . 193, 194
Hanover Four Corners, Mass.. Coal Measure beds.
near 194
Hardon mine, analyses of coal from 190, 191
High Hill Point, R. I.,, conglomerate at 278
Hills Grove Station, R. I., Carboniferous beds near. . 257
Hills Grove, R. I., sandstone at 334
Hitchcock, C. H., cited on supposed Devonian rocks. 141
cited on occurrence of coal near Cochesett Sta-
tion 192
coal near Cochesett Station shown on map of 192
features of geologic map prepared by 125, 133
Hitchcock, Edward, analysis of limestone by .--- 150
cited on age of the granite rocks 114
- cited on boundary of Carboniferous basin 127
cited on dip of beds near filansfield Junction...- 190
cited on flora of shales at Mansfield 191
Hitchcock, Edward, cited on occurrence of coal in
Fosboro 190
cited on Rosbury (=Dighton) conglomerate 184
cited on supposed Devonian and other rock
strata 141
cited on the»coal beds of tbe basin 205-207
cross section of Carboniferous area of Narragan-
sett Basin cited from 123
early attempts to discriminate geologic horizons
by 133
features of early geologic maps prepared by 124
Hoppin Hill, North Attleboro. Mass., Cambrian
rocks and fossils at and near 386,388-392
view of 384
Hope Island, R. I., rocks and features of 235-237. 341-342
Hornblende rock, occurrence and cbaracter of 117
Hunt, T. Sterry, geologic correlation of limestone of
Carboniferous basin suggested by 151
Hunts Mills, R. I., section at 169
Hyolithellus micans, occurrence of 388, 389, 393
Hyolithes americanus, occurrence of 390
Hyolithes biUingsi, occurrence of 389
Hyolithes communis, occurrence of 388, 392
Hyolithes communis var. emmonsi, occurrence of. . . 390, 392
Hyolithes micans, occurrence of 386
Hyolithes princeps, occurrence of 386, 389, 393
Hyolithes quadricostatus, occurrence of 390
I.
Igneous action, relation of plastic movement of rock
to 19
Igneous intrusions, difficulties of stratigraphic
determination occasioned by 101
Igneous rocks, occurrence and character of. . 152-155, 114-118
Insect fauna of the Rhode Island coal field, list
comprising 202, 203
Iron Hill, Cumberland, E. I., bowlder train at 72, 73, 76
iron ore of 89
Iron ores, occurrence of 88-90
Island Rocks, shales and slates of 286
J.
Jackson C. T., cited on coal beds at Portsmouth
mine 207
cited on coal bed in Cranston 206
cited on origin of Carboniferous clay slate 202
cited on primary rocks 104
cited on strike and dip of strata inclosing coal
beds 189,190
cited on strike and dip of strata inclosing coal
beds near Mansfield Junction. . . : 189. 190
features of early geologic map prepared by 124
Jacobs Point, conglomerate near 261
K.
Kingstown sandstones, divergent views of authors
as to value of --. xviii
geologic equivalents of 134,358,359,361-363
folding in 345,346,394
thickness of 345, 346
Kingstown series, geologic place and equivalents of. 134
occurrence and character of 159-104, 331-347
INDEX.
399
Page.
Kingstown aeries, Tiew of contact of pegmatite with . 242
view showing cross stratification in pebbly sand-
stone of 248
view showing sandstone gneiss of 334
L.
Landes, Harry, acknowledgments to 211
Lane, A. C, Cambrian fossils discovered by 388
LawtonsValley, E. I., rocks near 319,320,326,327
Lebanon Mills, Mass., section of boring near 170-172
Tenmile Kiver beds at 164
Leonards Corners, K. I., exposure of Tenmile Eiver
beds in quarry near 165
Lesqnereuj, L., cited on rarity of occurrence of
SigiUaria volzii 181
fossil plants identified by 191,204
Level, recent changes of 46-47
Lily Pond, K. I., granite near 31G
Lime Kock, K. I., Carboniferous shales of 309
limestone beds near 318
Lime Kock quarries, disconnected dike at 107, 108
Limestone, analysis of 150
Lingula antiqua, occurrence of 109
Lingula prima, occurrence of 109
Lithologic characters, rocks of different ages show-
ing duplication of 100
i-ocks of similar age showing local variations of. 100
Little Compton, K. I., Cambrian rocks in 383
shales and slates near 281,282
Little Lime Eock, E. I., Carboniferous shales of 309
Logan, "W.E., features of geologic map prepared by. 125
Logan and Hall cited 141
Lyell, Charles, early geologic map prepared by 133
features of geologic map prepared by 125
JSZ.
McCormick's quany, near Leonards Corners, E. I.,
exposure of Tenmile Eiver beds at 165
McCurry's Point, E.I., rocks near 290
Maclure, William, delineation of boundaries of Car-
boniferous basin by 124
Mansfield, analyses of coal from 191
Carboniferous beds near 188-191
coal beds at 79,80,205
fiora of shales at 191
gabbro and granitite at 118
section of Coal Measures in 190
section of rocbe moutonn^e near 188
Mansfield beds, table showing geologic place and
equivalents of. 134
Manton, Cumberland quartzite at 106-107
Map, geological 210, 394
Maps and sections of the Carboniferous basin . . 121, 122, 123
citations of 124-125
notes on 594
Marbut, C. F., and Griswold, L. S., cited on bound-
ary of Carboniferous basin 127-128
Margins of basin, greater folding at 16-18
Marine action in erosion and in land making, char-
acter and extent of 44-46, 76
Marthas Vineyard, deposits of arkose on 54
geologic history of 24
erogenic action in 24
Pliocene folding on 13
i of glacial deposit in ^ 71
Merrill, G. P., cited on diorite of Paradise Eocks
Metamorphism, dilficulties of strategraphic determi-
nation occasioned by
map showing areas of '.
Miantonomy Hill, E. I., conglomerates at and near.
Microdiscus bellimarginatus, occurrence of
Microdiscus lobatus, occurrence of
Middleboro quadrangle, Carboniferous beds in
Mill Cove, Boston Basin, Cambrian rocka and fossils
304, 305
369-371
390, 392
of.
Millers Eiver, Cumberland, E. I., conglomerate beds
at
geologic section of strata near
Millers Eiver conglomerates, table showing geologic
place and equivalents of
Moraines, frontal, characters of
Morton Park, E. I., rocks of ;
Mountain making, features of
Mount Desert Basin, geologic history of
Mount Hope, K. I., granite at
Mylacridse, occurrence of
Mylacris packardii, occurrence of
jS".
Kahant, Cambrian rOcka and fossils at 388
Nannaquacket Pond, granite near 272
Carboniferous rocks near 280-281
arkose and conglomerates near 378, 379
( Narragansett Pier, E. I., Carboniferous rocks at
and near 245-246
Natick, equivalence of Tiverton arkoses to those at. 379
rocks at and near 253-256, 375-376, 383-385
Neuropteris angustifolia, occurrence of 191
ISTeuropteris decipiens, occurrence of 204
Neuropteris dentata, occurrence of 204
iNeuropteris heterophylla, occurrence of 191
Neuropteroidea, occurrence of 202
Kewberry, J. S.,cited ou cycles of deposition 49
!N"ewport, E. I., Aquidneck shales near 356
coal beda at 207
coal seams and coal plants in excavations at 372
position of Carboniferous conglomerate at 373
strata beneath 313
Newport cliffs. Carboniferous rocka of 310-314
faulting near 310
fossil ferns found at 374
problematic geologic position of section at 371-372
Newport Harbor, rocks of islands in 307-310
Newport Neck, rocks of 316-318,383
Nonquit Point, Carboniferous rocka near 279
Nonquit Pond, sandstone and coaly shale near 275-276
Norfolk County basin, occurrence of red beds of
"Wamsutta group in 148-149
North Attleboro, Mass., basal arkose at 135
Cambrian rocks and fossils in and near 386-392
exposure of rocks of "Wamsutta group near 145-146
fossil plants found near 337
geologic section near 145
sketch map of Cambrian localties at 386
view of faulted diabase dikes in 152
view of granite mass at 334
view of outcrop of Wamsutta group in 146
North Foxboro, Mass., gabbro and granitite at 118
Norton, Mass'., section in 195-196
400
IISTDEX.
O. Page.
Obolella atlautica, occurrence of 390
Obolella crassa, occurrence of 390, 392
Obolns, occurrence of . . . 109, 110, 111, 112, 146, 314, 366, 382, 384
Obolus (Lingulella) rogersi, occurrence of 113
Obelus (Lingulobulus) affinis, occurrence of 113, 382
Obolus (Lingulobolus) rogersi, occurrence of 382
Obolus (Lingulobulus) epissus, occurrence of 113,382
Ocbre Point, conglomerate of 311-312
Odontopteria, occurrence of 170, 203-204
Oilontopteris bairdii, occurrence of 204
Odontopteria cornuta, occurrence of 204
Odontopteris neuropteroides, occurrence of 204
Odontopteris obtusiloba, occurrence of 204
Odontopteris reicbiana, occurrence of 20i
Odontopteris reichiana var. latifolia, occurrence of-. 204
Odoutopteris stiebleriana, occurrence of 204
Olenellus -walcotti, occurrence of 390
Olenellus zone, occurrence and character of rocks of. 8, 105,
38&-393
OUgocarpia gutbieri, occurrence of 204
Organic geology, features of 202-210
Orogenic action, features and results of 20-25, 32-36
Orogenic history, features of 7, 8, 9-10
Orthopteroidea, occurrence of 202-203
Overtlirust phenomena, character of 25-27
Pachet Brook, granite near 275
slates and shales near 281
Packard, A. S. , acknowledgments to 211
cited on fossils of Pawtucket shales 202
Palseoblattaripe, occurrence of 202
Paradise Eocks, conglomerates of 295-298
Paralogus asschnoides, occurrence of - . 203
Parsons, W. E., acknowledgments to 211
Passamaquoddy Basin, geologic history of 13-15
Pattaquamscott River, Carboniferous rocks near 246-247
Pawtucket, K. I., coal beds at 79
conglomerate in 141
Cranston, beds at and near 159-162
exposure of red rocks of "Wamsutta group at 148
fossil insects from 202, 203, 204
Pawtucket shales, exposures of 162
fossils of 202
table showing geologic place and equivalents of. 134
Pawtuxet Kiver, Carboniferous beds near 259
Pebbles, conditions of making of 56-58
compressive distortion of 18
Pecoi>teri8, occurrence of 168, 170, 191
Pecopteris abbreviata, occurrence of 204
Pecopteris arborescens, occurrence of 204
Pecopteris borealis, occurrence of 191
Pecopteris dentata, occurrence of 204
Pecopteris gigantea, occurrence of 191
Pecopteris hemiteloides, occurrence of 204
Pecopteris lepidorachis, occurrence of 204
Pecopteris loschii, occurrence of 191
Pecopteris miltoni, occurrence of 204
Pecopteris unita, occurrence of 170
Pegmatite dikes, view of 376
Pegmatites, views of 244
Pembroke, Mass.. Carboniferous and other rocks near 194
Perrins, anticlinal exposure of low beds at 169-170
Perry, J. H., cited 126
Pierces Pasture, near Pondville Station, Mass., sec-
tion at 135-13U
Plainville, Mass., section in 183
view of Carboniferous sandstones at 186
Plainville Valley, "Wrenthara, Mass., view of 180
Plants, fossil, occurrence of 170,
181, 204, 260, 261, 268, 275, 276, 285, 289, 293,
314, 320, 321, 326, 347, 363, 372, 374, 378, 387
Plastic movement of rock, regional distribution of . . lS-19
Platyceras prima; vum, occurrence of 390
Pleurotomaria (Kaphistoma) attleboroensis, occur-
rence of 389
Plympton felsites, occurrence and character of 116
Pondville, Mass., section in 135-136
Pondville group, features of beds of »... 135-141
table showing geologic place and equivalents of. 134
Fontiac, Carboniferous rocks near 256
Popasquash Neck, Carboniferous &andstone on 261
Portsmouth, R. I., analyses of coal from 83
Carboniferous rocks near 288-289
conglomerate in 373
coal beds at 81, 321
record of boring in 321-325
value of coal from 83-85
Portsmouth coal mine, operations at 206-207
Portsmouth Grove Station, rocks near 328-329
Potowomut River, Carboniferous rocks near 251-252
Potsdam sandstone, pebbles and fossils of 109-113
Pre-Cambrian rocks, occurrence, character, and re-
lations of 104-109
Pre-Carboniferous rocks, fossils of 381, 382, 383, 384
occurrence and character of 104-113, 381-385
Prices Neck, rocks near 316
Protophasmida, occurrence of 203
Providence, R. I., coal bed at 206
Cranston beds at and near 159-164
hypothetical geologic section through 160
record of well sunk at 161
view of glaciated Carboniferous ridge at 162
view of pre-Carboniferous rocka near 126
Providence River, Carboniferous beds near 259-260
synclinal fold in Kingstown series near 345
Prudence Island, R. I., rocks and geologic features
of 237-241,342-343,345,350-351
Prudence Island, Kingstown series on 342-343
views on 350. 352, 362
Pseudopecopteris dimorpha, occurrence of 204
Pseudopecopteris irregularis, occurrence of 191
Pty choparia attleboroensis, occurrence of 390
Purgatory chasm, typical conglomerate at 365-366
Purgatory conglomerate, occurrence and characterof 364—374
table showing geologic place and equivalents of. 134
Putnam, B. T., analyses by 83
Q.
356
Quaker Hill, Aquidneck shales near
Quartz, occurrence of 155
Quartzites, occurrence of 382, 383-384
Quartz-porphyries, occurrence of 153, 155
Raindrop imprints, view of 178
Rainfall and arkose, relations of 55-57
Raynham, coal bed in .; ' 205
INDEX.
401
Page.
Ked beds of "Wamsutta group, exposures of. 142-149
map showing areas of 142
Eed color of Cambrian and Carboniferous rocks, ori-
rrin of 62-63, 115
Eeaervoir Pond, Attleboro, Mass., section near 153
Ehacopbyllum adnascens, occurrence of 191
Kbapbidiopsis diveraipenna, occurrence of 202
Kbode Island Coal Measures, table sbowing geologic
place and eciuivalents of 134
Picbmond Basin, Virginia, geologic history of 13-15
Eidgway, Thos. S., cited on operations of the Mans-
field Coal and Mining Company 205
section of boring near Lebanon Mills made by .. 170-172
Elpple-marked sandstones, view of 178
Biverside, K. I., geological section at and near 166
synclinal fold in Kingstown Series near 345
Tenmile Eiver beds near 166
Eobinson Hill, North Attleboro, Mass., geologic sec-
tion at - 145
Eocky Hill, Providence, E. T., view of 162
Eocky Point, E. I., geologic horizon of conglomer-
ates of 346
Eocky Woods conglomerate, table showing geologic
place and equivalents of 134
Eoger "Williams coal mine, Cumberland, E. I., opera-
tions at 206
Eogers, 'W. B , cited on Potsdam sandstone 109
Eoselsland, E.I., rocksof 308,380
Eoxbury (— Digbton) conglomerate, occurrence of.. 184-187
Eumstick Neck, E. I., Carboniferous rocks on 260,344
synclinal fold near 345
Eussell, I. C., cited on coloration of rocks 115
S.
Sachems Eock, East Bridgewater, Mass., Coal Meas-
ure beds at 193
Sachuest Neck, E. I., arkose and pre- Carboniferous
rocks on 284-288,379
Sakonnet Eiver, conglomerates near 278-281
Sakonnet Eiver syncline, features of 369
Sakonnet sandstones, occurrence and thickness of . . 358,
359-360
Salterella curvata, occurrence of 386, 389
Sand Point, Prudence Island, E. I., micaceous shales
at - 239-240
Sandy Point, Aquidiieck Island, E. I., Carboniferous
shales near 289-290
Sapowet Point, E. I., Carboniferous rocks near 280
Saunderstown, E. 1., Carboniferous rocks near 242, 248
Kingstown series at 334
Scerella reticulata, occurrence of 390, 392
Scbizopteris (Ehacopbyllum) trichomanoides, occur-
rence of 204
Schrader, F. C, observations made by 106, 107
section of Goat Eock Cliff, near Plainville, meas-
ured by 180-181
Scolithus, occurrence of burrows of 197
Scholithus linearis, occurrence of 109, 110,112
Scudder, S.H., cited on insect fauna of tbe Ehode
Island coal field 202
Sears, John, Cambrian rocks and fossils discovered
by 388
Sections, geological 394
Sections and maps, notes on 394
Sedimentary deposits, thickness of 31
MON XXXIII 26
Sedimentation, cycles of 49-50
Seekonk, Mass., boring showing coal at 86
coal bed at 206
exposures and sections of Carboniferous rocks in . 169-173
Seekonk beds, occurrence and character of 173-175
Seekonk Coal Mining Company, section of boring
made for 170-172
Seekonk conglomerate, occurrence and character of . 174-175
table showing geologic place and equivalents of. 134
Seekonk sandstones, table showing geologic place
and equivalents of 134
Sewammock Neck, Mass., sandstone at 268
Shaler, N. S., Cambrian rocks discovered by 386
cited on increased erosion due to narrowing of
glacier 74
cited on Iron Hill bowlder train 72
cited on pre-Cambrian rocks 104
letter of transmittal by sv
preface by xvii-xx
report on general geology by 1-214
Shaler, N. S., and Foerste, A. P., cited on Cambrian
fossils from North Attleboro 109,141,386
Sharon, gabbro hills of 118
Sharpies, P. P., photographs made by 211
Shearing planes, areas showing 20-21
Sheep Point, rocks of 314^315
Sheldon ville, fault at 127
Shumatuscacant Eiver, fault near 129
Sigillaria ? occurrence of 165, 191
Sigillaria volzii, occurrence of 181
Silurian rocks, occurrence of pebbles from 109-113
Silver Spring, E. I., fossil insects from 203
view of Carboniferous sandstones at 166
Silver Spring Station, E. I., sections at and near . . . 166, 167
Sin and Plesb Brook, micaceous schist on 272
Slate Hill, E. I., rocks at and near 320,329-330,356,364
Smitbfield limestones, occurrence and character of. . 107-109
Smiths Beach, E.I., rocks near 292
Sueech Pond, E. I., copper and iron ores near 109
Cumberland quartzite at 106
Sockanosset Hill, E. I., Carboniferous beds at and
near 25fr-257
Sockanosset sandstones, exposures of 163
table sbowing geologic place and equivalents of. 134
Soils, character of 77-79
South Attleboro, limestone bed at 149-151
quartzose conglomerate near 140
section of "Wamsutta formation at 149
Spbenophyllum dentatum , occurrence of 191
Sphenophyllum equisetiformis, occurrence of 320
Spbenophyllum erasum, occurrence of 191
Sphenopbyllum oblongifolium, occurrence of 204
Sphenophyllum achlotbeimii, occurrence of 168
Sphenophyllum truncatum, occurrence of 191
Sphenopteris (Hymenophyllit«s) furcata, occurrence
of 204
Sphenopteris lanceolata, occurreuce of 204
Sphenopteris salisburyi, occurrence of 191
Spider, Carboniferous, occurrence of 202
Spindle Eock, Carboniferous shales of 309
Steep Brook, Mass., arkose deposits at 51-52
conglomerates near 378
granite and Carboniferous rocks at 269-270
Stenotheca curvirostra, occiurence of 390
Stenotheca rugosa, occurrence of 386, 388
Stenotheca rugosa var. abrupta, occurrence of 390, 392
402
INDEX.
Stenotlieca rugosa var. pauper, occurrence of 389
Stratigrapbic succession, difficulties of determiniug. 99-103
Stress, diagram showing conditions of 19
rock compression and elongation by 17-lB
Surf and current action, cliaracter and extent of
erosion by 76
Swansea, conglomerates and shales near 264-266, 373
Swamp areas, agricultural utilization of 78-79
Swan Point Cemetery, sandstone outcrox> at " 163-164
T.
Taggarts Ferry, Purgatory conglomerate at 364
Taunton, coal bed in 205
Coal Measures north and east of 187-201
record of artesian-well boring at 198-199
section near 199
Taunton quadrangle, Carboniferous beds in 195-200
Taunton Kiver, features of course of 200
Tenmile Eiver beds, exposures, sections, and fossils
of 164-173
plant remains in 164, 168, 170
table showing geologic place and equivalents of. 134
Teschemacher, J. E., x>lant remains from shales at
ilansfield described by 191
Till, thickness and character of 69-70
Tiverton, K. I., arkose in, 378
equivalence of ^Natick arkoses to those at 379
granite and Carboniferous rocks at 271-272
Tiverton Pour Corners, K. I., Carboniferous beds
near 280-281
granite at 274
Topsfield,. Mass., Cambrian rocks at 388
Tower, G- W., acknowledgments to 211
Tower Hill, K. I., Carboniferous and intrusive rocks
at 246-247
Town Pond, P. I., rocks near 321
Townsend Hill, Mass., granite and arkose at 270
Triassic rocks, eastern United States 11-12
Valley Palls. E.I., coal beds at 80,206
fossil insects from 204
Yalley Falls coalmine, operations at 206
YanHise, C. P., cited 125
Volcanoes, Carboniferous, geologic evidence indicat-
ing 155-166
Wadsworth, M. E., cited on age of granitic rocks 114
cited on iron, ore of Cumberland, P. 1 89
"Walcott, C. D., cited on age of chert pebbles from
Marthas Vineyard 113
Page.
TValcott, C. D., cited on brachiopod fauna of quartz-
itic pebbles from Carboniferous conglom-
erate 366, 382
cited on Cambrian fossils Ill, 113, 146. 366, 382
cited on intraformational conglomerates 189
cited on Upper Cambrian rocks 109
geologic horizon determined by 386
AVamsutta group, dikes in beds of 1 52
features of rocks of 141-158
flora of 158
folding of 15G-158
igneous associates of 152-155
section of 149
table showing geologic place and equivalents of. 134
view of outcrop of 146
volcanic rocks in 155-156
"Wainwright, Eobert, acknowledgments to 211
■\ralkers Cove, granite at 263
"Warren, P. I., conglomerates and shales near 266-267
AYarren Neck, P. I., Carboniferous beds on 264,373
Warwick, P. I., Kingstown series in 335,336,342
Warwick Keck. P. I., Carboniferous beds on.. . 258, 336-337
Watchemocket Cove, P. I., Tenmile River beds near. 166
Watsons Pier, P. I., Carboniferous rocks near 243-244
view of coarse pegmatites at 244
view of contact of i>egmatites and shales at 242
Wesquage Pond, P. I., rocks near 243, 333
West Mansfield, Mass., view of rocks at 188
West Newbury, Mass., Cambrian rocks in 3S8
Westville, Mass.. section in 199
Westville shales, table showing geologic place and
equivalents of 134
Whiteville, red rocks of Wamsutta group at 144
Wickford, Carboniferous rocks near 251
Wiokford Junction, Kingstown series at 344
Willis, Bailey, cited 168
Windmill Hill, P. I., conglomerates at and near 277
Winneconnet, Mass., Carboniferous beds near 196 197
map showing area of metamorphism near 120
Wolff, J. E , acknowledgments to 211
Woods Castle, Carboniferous rocks near 293
fossil ferns found at 293, 374
Woodworth, J.B., area examined by xvii
bibliography of Cambrian and Carboniferous
rocks prepared by 212-214
cited 141,167
description of the northern and eastern portion
of the basin prepared by 91-210
fossil plants discovered by 387
paper on northern and eastern portions of the
basin by 91-214
Wrentbam,Mass., coal bed in 182,205
exposures of Attleboro sandstone at 144-145
view near 180
[Monograph XXXIII.]
The statute approved March 3, 1879, establishing the United States Geological Survey, contains
the following provisions :
"The publications of the Geological Survey shall consist of the annual report of operations, geo-
logical and economic maps illustrating the resources and classification of the lands, and reports upon
general and economic geology and paleontology. The annual report of operations of the Geological
Survey shall accompany the annual report of the Secretary of the Interior. All special memoirs and
reports of said Survey shall be issued in uniform quarto series if deemed necessary by the Director, but
otherwise in ordinary octavos. Three thousand copies of each shall be published for scientific exchanges
and for sale at the price of publication ; and all literary aud cartographic materials received in exchange
shall be the property of the United States and form a part of the library of the organization : And the
money resulting from the sale of such liublioations shall be covered into the Treasury of the United
States."
Except in those cases in which au extra number of any special memoir or report has been sup-
plied to the Survey by special resolution of Congress or has been ordered by the Secretary of the
Interior, this oliBce has no copies for gratuitous distribution.
ANNUAL EEPOETS.
I. First Annual Keport of the United States Geological Survey, by Clarence King. 1880. 8°. 79
pp. 1 map. — A preliminary report describing plan of organization aud publications.
II. Second Annual Keport of the United States Geological Survey, 1880-'81, by J. W. Powell
1882. 8-^. Iv, 588 pp. 62 pi. 1 map.
III. Third Annual Eeport of the United States Geological Survey; 1881-'82, by J. W. Powell.
1883. 8". xviii, 56-1 iip. 67 pi. and maps.
IV. Fourth Annual Report of the United States Geological Survey, 1882-'83, by J. W. Powell.
1884. 8"^. xxxii, 473 pp. 83 pi. and maps.
V. Fifth Annual Eeport of the United States Geological Survey, 1883-'84, by J. W. Powell.
1885. 8°. xxxvi, 469 pp. 58 pi. and maps.
VI. Sixth Annual Eeport of the United States Geological Survey, 1884-'85, by J. W. Powell.
1885. 8°. xxix, 570 pp. 65 pi. and maps.
VII. Seventh Annual Eeport of the United States Geological Survey, 1885-'86, l)y J. W. Powell.
1888. 8°. XX, 656 pp. 71 pi. aud maps.
VIII. Eighth Annual Eeport of the United States Geological Survey, 1886-'87,.by J. W. Powell.
1889. 8°. 2 pt. xix, 474, xii pp., 53 pi. and maps; 1 pre]. .leaf, 475-1063 pp., 54-76 pi. and maps.
IX. Ninth Annual Report of the United States Geological Survev, 1887-'88, by J. W. Powell.
1889. 8". xiii, 717 pp. 88 pi. and maps.
X. Tenth Annual Eeport of the United States Geological Survey, 1888-'89, by J. W. Powell.
1890. 8°. 2 pt. XV, 774 pp., 98 pi. aud maps ; viii, 123 pp.
XI. Eleventh Annual Report of the United States Geological Survey, 1889-90, by J. W. Powell.
1891. 8"^. 2 pt. XV, 757 pp., 66 pi. and maps ; ix, 351 pp., 30 pi. and maps.
XII. Twelfth Annual Eeport of the United States Geological Survey, 1890-'91, by J. W. Powell.
1891. 8°. 2 pt., xiii, 675 pp., 53 pi. and maps ; xviii, .576 pi3., 146 j)l. and maps.
XIII. Thirteenth Annual Report of the United States Geological Survey, 1891-'92, by J. W.
Powell. 1893. 8"^. 3 pt. vii, 240 pp., 2 maps; x, 372 pp., 105 pi. and maps; x'i, 486 pp., 77 pi. and
maps.
XIV. Fourteenth Annual Report of the United States Geological Survey, 1892-'93, by J. W.
Powell. 1893. 8'^. 2 pt. vi, 321 pp., 1 pi. ; xx, 597 pp., 74 pi. and maps.
XV. Fifteenth Annual Eeport of the United States Geological Survey, 1893-'94, by J. W. Powell.
1895. 8'-\ xiv, 755 pp., 48 pi. and maps.
XVI. Sixteenth Annual Eeport of the United States Geological Survey, 1894-95, Charles D.
Walcott, Director. 1895. (Part I, 1896.) 8"^. 4 pt. xxii, 910 pp., 117 pi. and maps; xix, 598 pp., 43
pi. and maps; xv, 646 pp., 23 lA. ; xix, 735 pp., 6 pi.
XVII. Seventeenth Annual Eeport of the United States Geological Survey, 1895-96, Charles
D. Walcott, Director. 1896. 8". 3 pt. in 4 vol. xxii, 1076 pp., 67 pi. and maps; xxv, 864 pp., 113 pi.
and maps; xxiii, 542 pp., 8 pi. and maps; iii, 543-1058 pp., 9-13 pi.
XVIII. Eighteenth Annual Report of the United States Geological Survey, 1896-'97, Charles D.
Walcott, Director. 1897. (Parts II and III, 1898.) 8^. 5 pt. in 6 vol. 1-440 pp., 4 pi. and maps; i-v,
II ADVERTISEMENT.
1-653 pp., 105 pi. and maps; i-v, 1-861 pp., 118 pi. and maps: i-x, 1-756 pp., 102 pi. and maps; i-xii,
1-642 pp., 1 pi. ; 643-UOO pp.
XIX. Nineteenth Annual Report of the United States Geological Survey, 1897-'98, Charles D.
AValoott, Director. 1898. 8". 6 pt. in 7 vol.
MONOGRAPHS.
I. Lake Bonneville, by Grove Karl Gilbert. 1890. 4°. xx, 438 pp. 51 pi. 1 map. Price $1.50.
II. Tertiary History ofthe Grand Canon District, with Atlas, by Clarence E. Dutton, Capt., U. S. A.
1882. 4^. xiv, 264 pp. 42 pi. and atlas of 24 sheets folio. Price $10.00.
III. Geology of the Comstock Lode and the Washoe District, with Atlas, by George F. Becker.
1882. 4^^. XV, 422 pp. 7 pi. and atlas of 21 sheets folio. Price $11.00.
IV. Comstock Mining and Miners, by EliOt Lord. 1883. 4^. xiv, 451 pp. 3 pi. Price $1.50.
V. The Copper-Bearing Rocks of Lake Superior, by Roland Duer Irving. 1883. i^. xvi, 464
pp. 151. 29 pi. and maps. Price $1.85.
VI. Contributions to the Knowledge of the Older Mesozoic Flora of Virginia, by William Morris
Fontaine. 1883. 4°. xi, 144 pp. 54 1. 54 pi. Price $1.05.
VII. Silver-Lead Deposits of Eureka, l^evada, by Joseph Storv Curtis. 1884. 4°. xiii, 200 pp.
16 pi. Price $1.20.
VIII. Paleontology of the Eureka District, by Charles Doolittle Walcott. 1884. 4-. xiii, 298
pp. 24 1. 24 pi. Price $1.10.
IX. Brachiopoda and Lamellibranchiata of the Raritan Clays and Greensand Marls of New
Jersey, by Robert P. Whitfield. 1885. 4". xx, 338 pp. 35 pi. 1 map. Price $1.15.
X. Dinocerata. A Monograph of an Extinct Order of Gigantic Mammals, by Othniel Charles
Mnxsh. 1886. 4°. xviii, 243 pp. 56 1. 56 pi. Price $2.70.
XI. Geological History of Lake Lahontan, a Quaternary Lake of Northwestern Nevada, by
Israel Cook Russell. 1885. 4'^. xiv, 288 pj). 46 jil. and maps. Price $1.75.
XII. Geology and Mining Industry of Leadville, Colorado, with Atlas, by Samuel Franklin
Emmons. 1886. 4". xxix, 770 pp. 45 pi. aud atlas of 35 sheets foUo. Price $8.40.
XIII. Geology ofthe Quicksilver Deposits ofthe Pacific Slope, with Atlas, by George F.. Becker.
1888. 4^. xix, 486 pp. 7 pi. and atlas of 14 sheets folio. Price $2.00.
XIV. Fossil Fishes and Fossil Plants of the Triassic Rocks of New Jersey and the Connecticut
Valley, by John S. Newberry. 1888. 4°. xiv, 152 jip. 26 pi. Price $1.00.
XV. The Potomac or Younger Mesozoic Flora, by William Morris Fontaine. 1889. 4'^, xiv,
377 pp. 180 pi. Text and plates bound separately. Price $2.50.
XVI. The Paleozoic Fishes of North America, by John Strong Newberry. 1889. 4-. 340 pp.
53 pi. Price $1.00.
XVII. The Flora of the Dakota Group, a Posthumous Work, by Leo Lesquereux. Edited by
F. H. Kuowlton. 1891. 4". 400 pp. 66 pi. Price $1.10.
XVIII. Gasteropoda and Cephalopoda ofthe Raritan Clays aud Greensand Marls of New Jersev,
by Robert P. Whitfield. 1891. 4^. 402 jip. 50 pi. Price $1.00.
XIX. The Peuokee Iron-Bearing Series of Northern Wisconsin aud Michigan, by Roland D.
Irving and C. R. Van Hise. 1892. 4°. xix, 534 pp. Price $1.70.
XX. Geology of the Eureka District, Nevada, with an Atlas, by Arnold Hague. 1892. 4". xvii,
419 pp. 8 pi. Price $5.25.
XXI. The TertiarvRhyuchophorous Coleoptera ofthe United States, by Samuel Hubbard Scud-
der. 1893. i°. xi, 206 pp. 12 pi. Price 90 cents.
XXII. A Manual of Topographic Methods, by Henry Gannett, Chief Topographer. 1893. 4°.
xiv, 300 pp. 18 pi. Price $1.00.
XXIII. Geology ofthe Green Mountains in Massachusetts, by Raphael PumiJelly, T. Nelson Dale,
aud J. E. Wolff. 1894. i°. xiv, 206 pp. 23 j>l. Price $1.30.
XXIV. Mollusca aud Crustacea of the Miocene Formations of New Jersey, by Robert Parr Whit-
field. 1894. 4°. 193 pp. 24 pi. Price 90 cents.
XXV. TheGlacialLakeAgassiz, by Warren Upham. 1895. 4°. xxiv,658pp. 38 pL Price $1.70.
XXVI. Flora of the Amboy Clays, by John Strong Newberry; a Posthumous Work, edited by
Arthur Hollick. 1895. 4°. 260 pp. 58 pi. Price $1.00.
XXVII. Geology of the Denver Basin in Colorado, by Samuel Frauklin Emmons, Whitman Cross,
and George HomansEldridge. 1896. 4°. 556 pp. 31 pi. Price $1.50.
XXVIII. The Marquette Iron-Bearing District of Michigan, with Atlas, by C. R. Van Hise and
W. S. Bayley, includiug a Chapter on the Republic Trough, by H. L.Smyth. 1895. 4°. 608 pp. 35
pi. aud atlas of 39 sheets folio. Price $5.75.
XXIX. Geology of Old Hampshire County, Massachusetts, ccTiprising Frauklin, Hampshire, and
Hampden Counties, by Benjauiiu Kendall Emerson. 1898. 4°. xxi, 790 pp. 35 pi. Price $1.90.
XXX. Fossil Medusae, by Charles Doolittle Walcott. 1898. 4^. ix, 201 pp. 47 pi. Price $1.50.
XXXI. Geology of the Aspen Mining District, Colorado, with Atlas, by Josiah Edward Spurr.
1898. 4°. XXXV, 260 pp. 43 pi. aud atlas of 30 sheets folio. Price $3.60.
XXXII. Geology of the Yellowstone National Park, Part II, Descriptive Geology, Petrography,
and Paleoutology. by Arnold Hague, J. P. Iddiugs, W. Harvey Weed, Charles D. Walcott, G. H. Girty,
T. W. Stanton, and F. H. Knowlton. 1899. 4°. xvii, 893 pp. 121 pi. Price- .
XXXIII. Geology of the Narragansett Basin, by N. S. Shaler, J, B. Wood worth, and August F.
Foerste. 1899. 4°. xx, 402 pp. 31 pi. Price . '
ADVERTISEMENT. Ill
XXXV. The Later Extinct Floras of North America, by John Strong Newberry; edited by
Arthur Hollick. 1898. 4°. xviii, 295 pp. 68 pi. Price $1.25.
Jv preparation:
XXXIV. The Glacial Gravels of Maine and their Associated Deposits, by George H. Stone.
XXXVI. The Crystal Falls Iron-Bearing District of Michigan, by J. Morgan Clements and
Henry Lloyd Smyth; with a Chapter on the Sturgeon River Tongue, by William Shirley Bayley.
XXXVII. ilora of the Lower Coal Measures of Missouri, by David White.
XXXVIII. The Illinois Glacial Lobe, by Frank Leveiett.
— Flora of the Laramie and Allied Formations, by Frank Hall Knowltou.
BULLETINS.
1. On Hypersthene-Andesite and on Triclinic Pyroxene in Augitic Rocks, by Whitman Cross,
with a Geological Sketch of Buffalo Peaks, Colorado, by S. F. Emmons. 1883. 8°. 42 pp. 2 pi,
Price 10 cents.
2. Gold and Silver Conversion Tables, giving the Coining Values of Troy Ounces of Fine Metal,
etc., computed by Albert Williams, jr. 1883. 8*^. 8 pp. Price 5 cents.
3. On the Fossil Faunas of the Upper Devonian, along the Meridian of 76° 30', from Tompkins
County, N. Y., to Bradford County, Pa., by Henry S. AVilliams. 1884. 8'"-. 36 pp. Price 5 cents.
4. On Mesozoic Fossils, by Charles A. White. 1884. 8'^. 36 pp. 9 pi. Price 5 cents.
5. A Dictionary of Altitudes in the United States, compiled by Henry Gannett. 1884. 8°. 325
pp. Price 20 cents.
6. Elevations in the Dominion of Canada, by J. W. Spencer. 1884. 8°. 43 pp. Price 5 cents.
7. Mapoteca Geologica Americana. A Catalogue of Geological Maps of America (North and
South), 1752-1881, in Geographic and Chronologic Order, by Jules Marcou and John Belknap Maroon.
1884. 8°. 184 pp. Price 10 cents.
8. On Secondary Enlargements of Mineral Fragments in Certain Rocks, by R. D. Irving and
C. R. Van Hise. 1884. 8°. 56 pp. 6 pi. Price 10 cents.
9. A Report of Work done in the Washington Laboratory during the. Fiscal Year 1883-84. F. W.
Clarke, Chief Chemist; T. M. Chatard, Assistant Chemist. 1884. 8°. 40 pp. Price 5 cents.
10. On the Cambrian Faunas of North America. Preliminary Studies, by Charles Doolittle
Walcott. 1884. 8°. 74 pp. 10 pi. Price 5 cents.
11. On the Quaternary and Recent MoUusca of the Great Basin; -with Description of New
Forms, by R. Ellsworth Call. Introduced by a Sketch of the Quaternary Lakes of the Great Basin,
by G. K. Gilbert. 1884. 8°. 66 pp. 6 pi. Price 5 cents.
12. A Crystallographic Study of the Thinolite of Lake Lahontan, by Edward S. Dana. 1884. 8°.
34 pp. 3 pi. Price 5 cents.
13. Boundaries of the United States and of the Several States and Territories, with a Historical
Sketch of the Territorial Changes, by Henry Gannett. 1885. 8°. 135 pp. Price 10 cents.
14. The Electrical and Magnetic Properties of the Iron-Carburets, by Carl Barns and Vincent
Strouhal. 1885. 8*^. 238 pp. Price 15 cents.
15. On the Mesozoic and Cenozoie Paleontology of California, by Charles A. White. 1885. 8°.
33 px). Price 5 cents.
16. On the Higher Devonian Faunas of Ontario County, New Y'ork, by John M.Clarke. 1885. 8°.
86 pp. 3 pi. Price 5 cents.
17. On the Development of Crystallization in the Igneous Rocks of Washoe, Nevada, with Notes
on the Geology of the District, by Arnold Hague and Joseph P. Iddings. 1885. 8°. 44 pp. Price 5
cents.
18. On Marine Eocene, Fresh-Water Miocene, and other Fossil Mollusca of Western North
America, by Charles A. White. 1885. 8^. 26 pp. 3 pi. Price 5 cents.
19. Notes on the Stratigraphy of California, by George F. Becker. 1885. 8°. 28 pp. Price 5 cents.
20. Contributions to the Mineralogv of the Rocky Mountains, by Whitman Cross and W. F. Hille-
braud. 1885. 8°. 114 pp. 1 pi. Price' 10 cents.
21. The Lignites of the Great Sioux Reservation; a Rejiort on the Region between the Grand
and Moreau Rivers, Dakota, by Bailey Willis. 1885. 8°. 16 pp. 5 pi. Price 5 cents.
22. On New Cretaceous Fossils from California, by Charles A. White. 1885. 8°. 25 pp. 5 pi.
Price 5 cents.
23. Observations on the Junction between the Eastern Sandstone and the Keweenaw Series on
Keweenaw Point, Lake Superior, by R. D. Irving and T. C. Chamberlin. 1885. 8°. 124 pp. . 17 pi.
Price 15 cents.
24. List of Marine MoUusca, comprising the Quaternary Fossils and Recent Forms from American
Localities between Cape Hatteras and Cape Eoque, including the Bermuda.s, by William Healey Dall.
1885. 8^. 336 pp. Price 25 cents.
25. The Present Technical Condition of the Steel Industry of the United States, by Phiueas
Barnes. 1885. 8°. 85 pp. Price 10 cents.
26. Copper Smelting, by Henry M. Howe. 1885. 8°. 107 pp. Price 10 cents.
27. Report of Work done in the Division of Chemistry aud Physics, mainly during the Fiscal Year
1884-'85. 1886. 8°. 80 pp. Price 10 cents.
28. The Gabbros and Associated Hornblende Rocks occurring in the Neighborhood of Baltimore,
Maryland, by George Huntington Williams. 1886. 8°. 78 pp. 4 pi. Price 10 cents.
IV ADVERTISEMENT.
29. On tbe Fresli-AVater Invex'tebrates of the Nortli American Jurassic, by Charles A. AVbite. 1886.
8^. 41 pp. 4 pi. Price 5 cents.
30. Second Contribution to the Studies on the Cambrian Faunas of North America, by Charles
Doolittle Walcott. 1886. 8°. 369 pp. 33 pi. Price 2,5 cents.
31. Systematic Review of our Present Knowledge of Fossil Insects, including Myriapods and
Arachnids, by Samuel Hubbard Scudder. 1886. 8=. 128 pp. Price 15 cents.
32. Lists and Analyses of the Mineral Springs of the United States; a Preliminary Study, by
Albert C. Peale. 1886. 8°. 235 pp. Price 20 (/ents.
33. Notes on the Geology of Northern California, by J. S.Diller. 1886. 8°. 23 pp. Price 5 cents.
34. On till' liclatiouoftheLaramieMoUuscauFaunato that of the Succeeding Fresh-Water Eocene
and Other Gi(Mi|,N, l,y Charles A. White. 1886. 8^. 54 pp. 5 pi. Price lO.cents.
' 35. Plivsir;il rnipi-rties of the Iron-Carburets, by Carl Barns and Vincent Strouhal. 1886. 8-'.
62 pp. Price 10 cents.
36. Subsidenceof FineSolidParticlesinLiquids,byCaTlBarus. 1886. 8°. 58pp. PricelOcents.
37. Types of the Laramie Flora, by Lester F. Ward. 1887. 8°. 354 pp. 57 pi. Price 25 cents.
38. PeridotiteofElliottCounty,Kentucky, by J. S.Diller. 1887. 8^^. 31pp. Ipl. Price5cents.
39. The Upper Beaches and Deltas of the Glacial Lake Agassiz, bj' Warren Upham. 1887. 8°.
84 pp. 1 pi. Price 10 cents.
40. Changes in River Courses in AVashington Territory due to Glaciation, by Bailey Willis. 1887.
8-^. 10 pp. 4 pi. Price 5 cents.
41. On the Fossr. Faunas of the Upper Devonian — the Genesee Section, New York, by Henry S.
AVillianis. 1887. 8°. 121 iip. Ipl. Price 15 cents.
42. Reportof Work (biiic in liic 1 >i\i>ioii of Chemistryand Phy.sics, mainly during the Fiscal Year
1885-'86. F.W.Clarke, CliiciClMiiiiM. 1ns7. 8'-^. 1.52 pp. 1 pi." Price 15 cents.
43. Tertiary and Cretaceous Stiata of tlic Tuscaloosa, Tombigbee, and Alabama Rivers, by Eugene
A. Smith and Lawrence C. .Johnson. 1887. 8^. 189 pp. 21 pi. Price 15 cents.
44. Bibliography of North American Geology for 1886, by Nelson H. Darton. 1887. 8°. 35 pp.
Price 5 cents.
45. The Present Condition of Knowledge of the Geology of Texas, by Robert T. Hill. 1887. 8°.
94 pp. Price 10 cents.
46. Nature and Origin of Deposits of Phosphate of Lime, by E. A. F. Penrose, jr., with an Intro-
duction by N. S. Shaler. 1888. 8°. 143 pp. Price 15 cents.
47. Analyses of Waters of the Yellowstone National Park, with an Account of the Methods of
Analysis employed, liy Frank Austin Gooch and James Edward AVhitfield. 1888. 8°. 84 pp. Price
10 cents.
48. On the Form and Position of the Sea Level, by Robert Simpson AVoodward. 1888. 8"^. 88
pp. Price 10 cents.
49. Latitudes and Longitudes of Certain Points in Missouri, Kansas, and New Mexico, by Robert
Simpson AA^oodward. 1889. 8^. 133 pp. Price 15 cents.
50. Formulas and Taljles to Facilitate the Construction and Use of Maps, by Robert Simpson
AA^oodward. 1889. 8*^. 124 pp. Price 15 cents.
51. On Invertebrate Fossils from the Pacific Coast, by Charles Abiathar AVhite. 1889. 8^^. 102
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52. Subaerial Decay of Rocks and Origin of the Red Color of Certain Formations, by Israel
Cook Russell. 1889. 8°. 65 pp. 5 pi. PricelOcents.
53. The Geologv of Nantucket, by Nathaniel Southgate Shaler. 1889. 8'^. 55 pp. 10 pi. Price
10 cents.
54. On the Thermo-Electric Measurement of High Temperatures, Ijy Carl Barns. 1889. 8°.
313 pp., incl. 1 pi. 11 pi. Price 25 cents.
55. Report of AVork done in the Division of Chemistry and Phvsics, mainly during the Fiscal
Year 1886-'87. Frank AVigglesworth Clarke. Chief Chemist. 1889. 8^. 96 pp. Price lO'cents.
56. Fossil AVood ancl Lignite of the Potomac Formation, by Frank Hall Knowlton. 1889. 8^.
72 pp. 7 pi. Price 10 cents.
57. A Geological Reconnoissance In Southwestern Kansas, by Robert Hay. 1890. 8°. 49 pp.
2 111. Price 5 cents.
58. The Glacial Boundary in AVestern Pennsylvania, Ohio, Kentucky, Indiana, and Illinois, by
George Frederick AA'right, with an Introduction by Thomas Chrowder Chamberlin. 1890. 8°. 112
pp., incl. 1 pi. 8 pi. Price 15 cents.
59. The Galibros .and Associated Rocks in Delaware, by Frederick D. Chester. 1890. 8°. 45
pp. 1 pi. Price 10 cents.
60. Report of AA'ork done in the Division of Chemistry and Physics, mainly during the Fiscal
Year 1887-'88. F. W. Clarke, Chief Chemist. 1890. 8°. 174 pp. Price 15 cents.
61. Contributions to the Mineralogy of the Pacific Coast, by William Harlow Melville and AA'^al-
demar Lindgreu. 1890. 8^. 40 pp. 3 pi. Price 5 cents.
62. The Greenstone Schist Areas of the Menominee and Marquette Regions of Michigan, a Con-
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with an Introduction by Roland Duer Ir\'ing. 1890. 8°. 241 pp. 16 pi. Price 30 cents.
63. A Bibliography of Paleozoic Crustacea from 1698 to 1889, including a List of North Amer-
ican Species and a Systematic Arrangement of Genera, by Anthony W. Vogcles. 1890. 8^. 177 pp.
Price 15 cents.
64. A Report of AA''ork done in the Division of Chemistry and Physics, mainly during the Fiscal
Year 1888- 89. F. AV. Clarke, Chief Chemist. 1890. 8'-. 60 pp. PricelOcents.
ADVERTISEMENT. V
65. Stratigraphy of the Bituminous Coal Field of Penusvlvauia, Ohio, aucl West Virginia, by
Israel C. White. 1891. 8'^'. 212 pp. 11 pi. Price 20 cents. '
66. On a Group of Volcanic Eocks from the Tewan Mountains, New Mexico, and on the Occur-
rence of Primary Quartz in Certain Basalts, by Joseph Paxson Iddings. 1890. 8<^. 34 pp. Price 5
cents.
67. The Relations of the Traps of the Newark System in the New Jersey Region, by Nelson
Horatio Darton. 1890. 8'^. 82 pp. Price 10 cents.
68. Earthquakes in California in 1889, by James Edward Keeler. 1890. 8^. 25 pp. Price 5
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69. A Classed and Annotated Biography of Fossil Insects, by Samuel Howard Scudder. 1890.
8°. 101 pp Price 15 cents.
70. A Report on Astronomical Work of 1889 and 1890, by Robert SLmpsou Woodward. 1890. 8^^.
79 pp. Price 10 cents.
71. Index to the Known Fossil Insects of the World, including Myriapods and Arachnids, by
Samuel Hubbard Scudder. 1891. 8°. 744 pp. Price 50 cents.
72. Altitudes between Lake Superior and the Rocky Mountains, by Warren Upham. 1891. 8^.
229 px). Price 20 cents.
73. The Viscosity of Solids, by Carl Barns. 1891. 8'-\ xii, 139 pp. 6 pi. Price 15 cents.
74. The Minerals of North Carolina, by Frederick Augustus Genth. 1891. 8*^. 119 pp. Price
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75. Record of North American Geology for J887 to 1889, inclusive, bv Nelson Horatio Darton.
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76. A Dictionary of Altitudes in the United States (Second Edition), compiled by Henry Gannett,
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77. The Texan Permian and its Mesozoic Types of Fossils, by Charles A. White. 1891. 8°. 51
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78. A Report of Work done in the Division of Chemistry and Physics, mainly during the Fiscal
Year 1889-'90. F. AV. Clarke, Chief Chemist. 1891. 8". 131 pp. Price 15 cents.
79. A Late Volcanic Eruption in Northern California and its Peculiar Lava, by J. S. Diller.
80. Correlation Papers — Devonian and Carboniferous, by Henry Shaler Williams. 1891. 8°.
279 pp. Price 20 cents.
81. Correlation Papers — Cambrian, by Charles Doolittle Walcott. 1891. 8°. 547 pp. 3 pi.
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82. Correlation Papers— Cretaceous, by Charles A. White. 1891. 8'^. 273 pp. 3 pi. Price 20
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83. Correlation Papers — Eocene, by William Bullock Clark. 1891. 8°. 173 pp. 2 pi. Price
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84. Correlation Papers— Neocene, by W. H. Dall and G. D. Harris. 1892. 8>=. 349 pp. 3 pi.
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85. Correlation Papers — The Newark System, by Israel Cook Russell. 1892. 8°. 344 pp. 13 pi.
Price 25 cents.
86. Correlation Papers— Archeau and Algonkian, by C.R. Van Plise. 1892. 8^\ ,549 pp. 12 pi.
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87. A Synopsis of American Fossil. Brachiopoda, including Bibliography and Synonymy, by
Charles Schuchert. 1897. 8'-. 464 pp. Price 30 cents.
88. The Cretaceous Foraminifera of New Jersey, by Rufus Mather Bagg, Jr. 1898. 8^. 89 pp.
6 pi. Price 10 cents.
89. Some Lava Flows of the Western Slope of the Sierra Nevada, California, by F. Leslie
Ransome. 1898. 8°. 74 pp. 11 pi. Price 15 cents.
90. A Report of Work done in the Division of Chemistry and Physics, mainly during the Fiscal
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91. Record of North American Geology for 1890, by NeLson Horatio Darton. 1891. 8°. 88 pp.
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92. The Compressibility of Liquids, by Carl Barns. 1892. 8°. 96 pp. 29 pi. Price 10 cents.
93. Some Insects of Special Interest from Florissant, Colorado, and Other Points in the Tertiaries
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94. The Mechanism of Solid Viscosity, by Carl Barns. 1892. 8°. 138 pp. Price 15 cents.
95. Earthquakes in California in 1890 and 1891, by Edward Singleton Holden. 1892. 8°. 31pp.
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96. The Volume Thermodynamics of Liquids, by Carl Barus. 1892. 8-^. 100 pp. Price 10 cents.
97. The Mesozoic Echinodermata of the United States, by W.B. Clark. 1893. 8'^. 207 pp. oOpl.
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98. Flora of the Outlying Carboniferous Basins of Southwestern Missouri, by David White.
1893. 8^. 139 pp. 5 pi. Price 15 cents.
99. Record of North American Geology for 1891, by Nelson Horatio Darton. 1892. 8°. 73 pp.
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■ 100. Bibliography and Index of the Publications of the U. S. Geological Survey, 1879-1892, by
Philip Creveliug Warman. 1893. 8-. 495 jip. Price 25 cents.
101. Insect Fauna of the Rhode Island Coal Field, by Samuel Hubbard Scudder. 1893. 8"^.
27 pp. 2 pi. Price 5 cents.
102. A Catalogue and Bibliography of North American Mesozoic Invertebrata, by Cornelius
Breckinridge Boyle. 1892. 8^. 315 pp. Price 25 cents.
VI ADVERTISEMENT.
103. High Temperature Work in Igneous Fusion and Ebullitiou, chiefly in Relation to Pressure,
hy Carl Barus. 1893. 8°. 57 pp. 9 pi. Price 10 cents.
104. Glaciation of the Yellowstone Valley north of the Park, by Walter Harvey Weed. 1893. 8^.
41 pp. 4 pi. Price 5 cents.
105. The Laramie and the OA'erlying Livingstone Formation in Montana, by Walter Harvey
Weed, with Report on Flora, by Frank Hall Knowlton. 1893. 8^. 68 pp. 6 pi. Price 10 cents.
106. The Colorado Formation and its Invertebrate Fauna, by T. W. Stanton. 1893. 8^. 288
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107. The Trap Dikes of the Lake Champlain Region, by James Fnrman Kemp and Vernon
Freeman Marsters. 1893. 8'-^. 62 pp. 4 pi. Price 10 cents.
108. A Geological Reconnoissanoe in Central AVashington, by Israel Cook Russell. 1893. 8-".
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109. The Eruptive and Sedimeutary Rocks on Pigeon Point, Minnesota, and their Contact Phe-
nomena, by William Shirley Bayley. 1893. 8". 121 pp. 16 pi. Price 15 cents.
110. The Paleozoic Section in the Vicinity of Three Forks, Montana, by Albert Charles Peale.
893. 8°. 56 pp. 6 pi. Price 10 cents.
111. Geology of the Big Stone Gap Coal Fields of Virginia and Kentucky, by Marius R. Camp-
bell. 1893. 8^. 106 pp. 6 pi. Price 15 cents.
112. Earthquakes in California in 1892, by Charles D. Perrine. 1893. 8^. 57 pp. Price 10 cents.
113. A Report of Work done in the Division of Chemistrv during the Fiscal Years 1891-'92 and
1892-'93. F. W. Clarke, Chief Chemist. 1893. 8°. 115 pp. Price 15 cents.
114. Earthquakes in California in 1893, by Charles D. Perrine. 1894. 8^. 23 pp. Price 5 cents.
115. A Geographic Dictionary of Rhode Island, by Henry Gannett. 1894. 8°. 31 pp. Price
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116. A Geographic Dictionary of Massachusetts, by Henry Gannett. 1894. 8^. 126 pp. Price
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117. A Geographic Dictiouai-y of Connecticut, by Henry Gannett. 1894. 8°. 67 pp. Price 10
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118. A Geographic Dictionary of New Jersey, by Henry Gannett. 1894. 8^. 131 pp. Price 15
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119. A Geological Reconnoissance in Northwest Wyoming, by George Homans Eldridge. 1894.
8°. 72 pp. Price 10 cents.
120. The Devonian System of Eastern Pennyslvania and New York, by Charles S. Prosser. 1894.
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121. A Bibliography of North American Paleontology, by Charles Rollin Keyes. 1894. 8"^. 251
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122. Results of Primary Triangnlation, by Henry Gannett. 1894. 8'^. 412 pp. 17 pi. Price
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123. A Dictionary of Geographic Positions, by Henry Gannett. 1895. 8°. 183 pp. 1 pi. Price
15 cents.
124. Revision of North American Fossil Cockroaches, by Samuel Hubbard Scudder. 1895. 8^.
176 pp. 12 pi. Price 15 cents.
125. The Constitution of the Silicates, by Frank Wigglesworth Clarke. 1895. 8^=. 109 pp.
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126. A Mineralogical Lexicon of Franklin, Hampshire, and Hampden counties, Massachnsetts,
by Benjamin Kendall Emerson. 1895. 8^. 180 pp. 1 pi. Price 15 cents.
127. Catalogue and Index of Contributions to North American Geology, 1732-1891, by Nelson
Horatio Darton. 1896. 8°. 1045 pp. Price 60 cents.
128. The Bear River Formation and its Characteristic Fauna, by Charles A. White. 1895. 8^.
108 pp. 11 pi. Price 15 cents.
129. Earthquakes in California in 1894, by Charles D. Perrine. 1895. 8^~. 25 pp. Price 5 cents.
130. Bibliography and Index of North American Geology, Paleontology, Petrology, and Miner-
alogy for 1892 and 1893, by Fred Boughton Weeks. 1896. 8-\ 210 pp. Price 20 cents. '
131. Report of Progress of the Division of Hydrography for the Calendar Years 1893 and 1894,
by Frederick Haynes Newell, Topographer in Charge. 1895. 8°. 126 pp. Price 15 cents.
132. The Disseminated Lead Ores of Southeastern Missouri, by Arthur Wiuslow. 1896. 8°.
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133. Contributions to the Cretaceous Paleontology of the Pacific Coast: The Fauna of the
Knoxville Beds, by T. W. .Stanton. 1895. 8-\ 132 pp. 20 pi. Price 15 cents.
134. The Cambrian Rocks of Pennsylvania, by Charles Doolittle Walcott. 1896. 8°. 43 pp.
15 pi. Price 5 cents.
135. Bibliography and Index of North American Geology, Paleontology, Petrology, and Miner-
alogy for the Y'ear 1894, by F. B. Weeks. 1896. 8*^. 141 pp. Price 15 cents.'
136. Volcanic Rocks of South Mountain, Pennsylvania, by Florence Bascom. 1896. 8'^. 124 pp.
28 pi. Price 15 cents.
137. The Geology of the Fort Riley Military Reservation and Vicinity, Kansas, by Robert Hay.
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138. Artesian-Well Prospects in the Atlantic Coastal Plain Region, by N. H. Darton. 1896. 8"^.
228 pp. 19 pi. Price 20 cents.
139 Geology of the Castle Mountain Mining District, Montana, by W. H. Weed and L. V. Pirs-
son. 1896. 8°. 164 pp. 17 pi. Price 15 cents.
140. Report of Progress of the Division of Hydrography for the Calendar Year 1895, by Frederick
Haynes Newell, Hydrographer in Charge. 1896. 8"^. 356 pp. Price 25 cents.
ADVERTISEMEIs^T. VII
Ul. The Eocene Deposits of tlie Middle Atlantic Slope in Delaware, Maryland, and Virginia,
1)T William Bullock Clark. 1896. 8°. 167 pp. 40 pi. Price 15 cents.
142 A Brief Contribution to the Geology and Paleontology of Northwestern Louisiana, by
T. Wayland Vaughan. 1896. 8°. 65 pp. 4 pi. Price 10 cents ,^nn o-> -,-,,
143. A Bibliography of Clays and the Ceramic Arts, by John C. Branner. 1896. 8^. 114 pp.
144. The Moraines of the Missouri Coteau and their Attendant Deposits, by James Edward Todd.
1896. 8°. 71 pp. 21 pi. Price 10 cents.
145. The Potomac Formation in Virginia, by W. M. Fontaine. 1896. 8^. 149 pp. 2 pi. Price
146. Bibliography and Index of North American Geology, Paleontology, Petrology, and Miner-
alooy for'the Year 1895, by F. B. AVeeks. 1896. 8'\ 130 pp. Price 15. cents.
° 147. Earthquakes in California in 1895, by Charles D. Perrine, Assistant Astronomer in Chargo
of Earthquake Observations at the Lick Observatory. 1896. 8'-. 23 pp. Price 5 cents.
148 Analyses of Rocks, with a Chapter on Analytical Methods, Laboratory of the United States
Geological Survey, 1880 to 1896, by F. W. Clarke and W. F. Hilleljraud. 1897. 8^^. 306 pp. Price
149. Bibliography and Index of North American Geology, Paleontology, Petrology, and Miner-
alogy for the Year 1896, by Fred Boughton Weeks. 1897. 8°. 152 pp. Price 15 cents.
150. The Educational Series of Rock Specimens collected and distributed by the United States
Geological Survey, bv Joseph Silas Diller. 1898. 8°. 398 pp. 47 pL Price 25 cents.
151. The Lower Cretaceous Gryphicas of the Texas Region, by R. T. Hill and T. Wayland
Vaughan. 1898. 8°. 139 pp. 25 pi. Price 15 cents.
152. A Catalogue of the Cretaceous and Tertiary Plants of North America, by F. H. Knowlton.
1898. 8°. 247 pp. Price 20 cents.
153. A Bibliographic Index of North American Carboniferous Invertebrates, by Stuart Weller.
1898. 8°. 653 pp. Price 35 cents.
154. A Gazetteer of Kansas, by Henry Gannett. 1898. 8°. 246 pp. 6 pi. Price 20 cents.
155. Earthquakes in California in 1896 and 1897, by Charles D. Perrine, Assistant Astronomer
in Charge of Earthquake Observations at the Lick Observatory. 1898. 8°. 47 pp. Price 5 cents.
156. Bibliography and Index of North American Geologj', Paleontology, Petrology, and Miner-
alogy for the Y'ear 1897, by Fred Boughton Weeks. 1898. 8^. 130 pp. Price 15 cents.
160. A Dictionary of Altitudes in the United States (Third Edition), compiled by Henry
Gannett. 1899. 8^. 775 pp. Price 40 cents.
161. Earthquakes in California in 1898, by Charles D. Perrine, Assistant Astronomer in Charge
of Earthquake Observations at the Lick Observatory. 1899. 8°. 31pp. 1 pi. Price 5 cents.
Ill preparation: ^ , „ ,_
157. The Gneisses, Gabbro-Schists, and Associated Rocks of Southeastern Minnesota, by C. W.
158. The Moraines of southeastern South Dakota and their Attendant Deposits, by J. E. Todd.
159. The Geology of Eastern Berkshire County, Massachusetts, by B. K. Emerson.
WATER-SUPPLY AND IRRIGATION PAPERS.
By act of Congress approved June 11, 1896, the following provision was made:
"Propidecl, That hereafter the reports of the Geological Survey in relation to the gauging of
streams and to the methods of utilizing the water resources may be priu'ed in octavo form, not to
exceed one hundred pages in length and live thousand copies in number ; oue thousand copies of which
shall be for the ofiflciaruse of the C4eological Survey, one thousand five hundred copies shall be deliv-
ered to the Senate, and two thousand five hundred copies shall be delivered to the House of Repre-
sentatives, for distribution."
Under this law the following papers have been issued:
1. Pumping Water for Irrigation, by Herbert M. ^" ilson. 1896. 8-^. 57 pp. 9 pi.
2. Irrigation near Phtt'uix, Arizona,' by Arthur P. Davis. 1897. 8°. 97 pp. 31 pi.
3. Sewage Irrigation, bv George W. Rafter. 1897. 8^. 100 pp. 4 pi.
4. A Reconnoissance in Southeastern Washington, by Israel Cook Russell. 1897. 8°. 96 pp. 7 pi.
5. Irrigation Practice on the Great Plains, by Elias Branson Cowgill. 1897. 8^. 39 pp. 12 pi.
6. Underground Waters of Southwestern Kansas, by Erasmus Haworth. 1897. 8°. 65 pp. 12 pi.
7. Seepage Waters of Northern Utah, by Samuel Fortier. 1897. 8°. 50 pp. 3 pi.
8. Windmills for Irrigation, by Edward Charles Murphy. 1897. 8^. 49 pp. 8 pi.
9. Irrigation near Greeley, Colorado, by David Boyd. 1897. 8'=. 90 pp. 21 pi.
10. Irrigation in Mesilla Valley, New Mexico, by F. C. Barker. 1898. 8°. 51 pp. 11 pi.
11. River Heights for 1896, by Arthur P. Davis. 1897. 8*^. 100 pp.
12. Water Resources of Southeastern Nebraska, by Nelson H. Darton. 1898. 8°. 55 pp. 21 pL
13. Irrigation Systems in Texas, by William Ferguson Hutson. 1898. 8^''. 67 pp. 10 pi.
14. New Tests of Certain Pumps and AVater-Lifts used in Irrigation, by Ozni P. Hood. 1889. 8°.
91 pp. 1 pi.
15. Operations at River Stations, 1897, Part I. 1898. 8'^. 100 pp.
16. Operations at River Stations, 1897, Part II. 1898. 8^. 101-200 pp.
17. Irrigation near Bakersfield, California, by C. E. Grunsky. 1898. 8°. 96 pp. 16 pi.
18. Irrigation near Fresno, California, by C. E. Grunsky. 1898. 8°. 94 pp. 14 pi.
19. Irrigation near Merced, California, by C. E. Grunsky. 1899. 8°. 59 pp. 11 pi.
20. Experiments with Windmills, by T. O. Perry. 1899. 8°. 97 pp. 12 pi.
VIII
ADVEETISEMF.NT.
21. Wells of Northern Intliana, by Frank Leverett. 1899. 8°. 82 pp. 2 pi.
22. Sowase Irrigation, Part II, by George AV. Kaiter. 1899. 8--". 100 pp. 7 pi.
23. Water-Right Problems of Bighorn Mountains, by Elwood Mead. 1899. 8"^. 62 pp. 7 pi.
24. Water Eesonrces of the State of New York, Part I, by George \V. Rafter. 1899. 8°.
99pp. 13 pi.
25. Water Resources of the State of New York, Part II, by George W. Rafter. 1899. 8°.
101-200 pp. 12 pi.
26. Wells of Southern Indiana (Continuation of No. 21), by Frank Leverett. 1899. 8^. 64 pp.
In ijress:
27. Operations at River Stations, 1898, Part I. 1899. 8-=. 100 pp.
28. Operations at River Stations, 1898, Part II. 1899. 8^. 101-200 pp.
In preparation :
29. Wells and Windmills in Nebraska, by Edwin H. Barbour.
30. Water Resources of the Lower Peninsula of Michigan, by Alfred C. Lane.
TOPOGRAPHIC MAP OF THE UNITED STATES.
When, in 1882, the Geological Survey was directed by law to make a geologic map of the United
States there was in existence no suitable topographic map to serve as a base for the geologic map.
The preparation of such a topogi-.iphic map was therefore immediately begun. About one-fifth of the
area of the country, excluding Alaska, has now been thus mapped. The map is published in atlas
sheets, each sheet representing a small quadrangular district, as explained under the next head-
ing. The separate sheets are sold at 5 cents each when fewer than 100 copies are purchased, but when
they are ordered in lots of 100 or more copies, whether of the same sheet or of dilferent sheets, the
price is 2 cents each. The mapped areas are widely scattered, nearly every State being represented.
About 900 sheets have been engraved and printed; they are tabulated by States in the Survey's
"List of Publications," a pamphlet which may be had on application.
The map sheets represent a great variety of topographic features, and with the aid of descriptive
text they can be used to illustrate topographic forms. This has led to the projection of an educational
series of topographic folios, for use wherever geography is taught in high schools, academies, and
colleges. Of this series the first folio has been issued, viz:
1. Physiographic types, by Henry Gannett, 1898, folio, consisting of the following sheets and 4
Images of descriptive text: p'argo (N. Dak.-Minn.), a region in youth; Charleston (W.Va.),a region in
maturity; Caldwell (Kans.), a region in old age; Palmyra (Va.), a rejuvenated region ; Mount Shasta,
(Cal.), a young volcanic mountain; Eagle (Wis.), moraines; Sun Prairie (Wis.), drumlins; Donald-
sonville (La.), river flood plains; Boothbay (Me.), a fiord coast; Atlantic City (N. J.), a barrier-beach
coast.
GEOLOGIC ATLAS OF THE UNITED STATES.
The Geologic Atlas of the United States is the final form of publication of the topographic and
geologic maps. The atlas is issued in parts, progressively as the surveys are extended, and is designed
ultimately to cover the entire country.
Under the plan adopted the entire area of the country is divided into small rectangular districts
(designated quadrangles), bounded by certain meridians and jiarallels. The unit of survey is also the
unit of publication, and the maps and descriptions of each rectangular district are issued as a folio of
the Geologic Atlas.
Each folio contains topographic, geologic, economic, and structural maps, together with textual
descriptions and explanations, and is designated by the name of a principal town or of a prominent
natural feature withiu the district.
Two forms of issue have been adopted, a "library edition" and a "field edition." In both the
sheets are bound between heavy i^aper covers, but the library copies are permanently bound, while
the sheets and covers of the field copies are only temporarily wired together.
Under the law a copy of each folio is sent to certain public libraries and educational institu-
tions. The remainder are sold at 25 cents each, except such as contain an unusual amount of matter,
which are priced accordingly. Prepayment is obligator}'. The folios ready for distribution are listed
below.
No.
I^ame of sheet.
State.
Limiting meridians.
Limiting parallels.
A.rea, in
square
miles.
Price,
cents.
Montana
/Georgia
110°-H1°
\ 85°-So° 30'
120° 30'-121°
84° 3U'-85o
1210-121° 30'
850-85° 30'
105°-105° 30'
85° 30'-86°
106° 45'-107° 15'
1 77° 30'-78°
4d°-46°
34° 30'-35°
38° 30'-39°
35° 30'-36°
38° 30'-39°
35°-35° 30'
38° 30'-39°
35°-35° 30'
38° 45'-39o
390-39° 30'
3,354
98U
932
969
932
975
932
975
465
925
0-
25
25
t
California
Tennessee
California
Tennessee
Colorado
Tennessee
Colorado
(Virginia
West Virginia..
iKaryland
i\
25
25
6
7
Cliattauooga
Pikes Peak (out of stock)
25
25
25
9
10
Anthracite-Crested Butte
Harpers Ferry
50
25
ADVERTISEMENT.
Limitins meridians
Limiting parallels
Area, ir
square
miles.
Prici',
cents.
Jackson ...
Estillville ,
Fredericksburg.
Staunton
Lassen Peak
Knoxville
Stevenson ...
Cleveland
Pikeville
McMinnville.
Noniini
26 I Pocahontas .
27 iloiTistovrn.
28 Piedmont...
California
(Virginia
Kentucky
Tennessee
/Maryland
\Yirginia
/Virginia
tWest Virginia.
California
Tennessee
Korth Carolina
California
California
(Alabama
•^Georgia
(Tennessee
Tennessee
Tennessee
Tennessee
/Maryland
Montana.
(iSrevadaCitv.i
Nevada City ... { Grass YalleV .
(Banner Hili .J
fGallatin .
/Yellowstone Na- I Canyon..
\\ tional Park. ) Shoshone
[Lake....
Pyramid Peak
' Franklin
BriceviUe
Buckbannon
Gadsden
Pneblo
Downieville
Butte Special
Truckee
■VYartburg
Sonora
W-
43 Bid well Ba
44 I Tazewell..
Boise
Kicbraond
London
Tenmile District Special.
Roseburg
Hoi yoke
California
/■Virginia
\West Virginia .
Tennessee
West Virginia
Alabama
Colorado
California
Montana
California
Tennessee
California
California" !!!.'.'
/Virginia
nv est Virginia.
Idaho
Kentucky
Kentucky
Colorado
120° 30'-121o
820 30'-83°
770-77° 30'
79°-79° 30'
84° 30'-85°
850-85° 30'
850 30'_S6o
00' 25"-121o 03' 45"
' 01' 35"-121° 05' 04"
57' 05"-121o 00' 25"
120°-120o 30'
■90-790 30'
1040 30'-105o
120° 30'-121°
20' 30"-112° 36' 42"
1200-120° 30'
84° 30'-85°
1200-120° 30'
1000-100° 30'
1210-121° 30'
81° 30'-82°
1160-1160 30'
840-84° 30'
S4°-84o 30'
106° 8'-106o 16'
1230-1230 30'
720 30'-73°
38°-38° 30'
36° 30'-37°
3SO-38° 30'
40°-41°
350 30'-36°
350-350 30'
35° 30'-36°
35° 30'-36°
39° 13' 50"-39" 17' 16"
390 10' 22"-39° 13' 50"
390 13' 60"-39o 17' 16"
38° 30'-39°
38° 30'-39o
360-36° 30'
38° 30'-39o
340-340 30'
380-38° 30'
39° 30'-40°
450 59' 28"-46o 02' 54"
39°-39° 30'
360-36° 30'
370 30'-38o
29° 30'-30o
39° 30'-40°
0-37° 30'
11.65
12.09
11.65
STATISTICAL PAPERS.
Mineral Resources of the United States [1882], by Albert Williams, jr. 1883. 8^. xvii813iip.
Price 50 cents. ' ' '
Mineral Resources of the United States, 1883 and 1884, bv Albert AVilliams, ir. 188.5 8° xiv
1016 pp. Price 60 cents. ' j • ,
Mineral Resources of the United States, 1885. Division of Mining Statistics and Technolooy
1886. 8°. vii, 576 pp. Price 40 cents.
Mineral Resources of the United States, 1886, by David T. Day. 1887. 8°. viii, 813 pp. Price
60 cents.
Mineral Resources of the United State.s, 1887, by David T. Day. 1888. 8'^. vii, 832 pp. Price
50 cents.
Mineral Resources of the United States, 1888, by David T. Day. 1890. 8'='. vii, 652 pp. Price
50 cents.
Mineral Resources of the United States, 1889 and 1890, by David T. Day. 1892. 8'='. viii, 671 pp.
Price 50 cents.
Jliueral Resources of the United States, 1891, by David T. Day. 1893. 8^. vii, 630 pp. Price
X ADVERTISEMENT.
Mineral Resources of the United States, 1892, by DaTid T. Day. 1893 8=. vii, 850 pp. Price
50 cents.
Mineral Resources of the United States, 1893, by David T. Day. 1894. 8°. viii, 810 pp. Price
50 cents.
On March 2, 1895, the following provision was included in an act of Congress:
"Provided, That hereafter the report of the mineral resources of the United States shall be
issued as a part of the report of the Director of the Geological Survey."
In compliance veith this legislation the following reports have been published :
Mineral Resources of the United States, 1894, David T. Day, Chief of Division. 1895. 8°. xv,
646 pp., 23 pi. ; xix, 735 pp., 6 pi. Being Parts III and IV of the Sixteenth Annual Report.
Mineral Resources of the United States, 1895, David T. Day, Chief of Division. 1896. 8°.
xxiii, 542 pp., 8 pi. and maps; iii, .543-1058 pp., 9-13 pi. Being Part III (in 2 vols.) of the Seventeenth
Annual Report.
Mineral Resources of the United States, 1896, David T. Day, Chief of Division. 1897. 8°.
xii, 642 pp., 1 pi. ; 643-1400 pp. Being Part V (in 2 vols.) of the Nineteenth Annual Report.
Mineral Resources of the United States, 1897, David T. Day, Chief of Division. 1898. 8°.
viii, 651 pp., 11 pi. ; viii, 706 pp. Being Part VI (in 2 vols.) of the Nineteenth Annuaf Report.
The money received from the sale of the Survey publications is deposited in the Treasury, and
the Secretary of that Department declines to receive bank checks, drafts, or postage stamps ; all remit-
tances, therefore, must be by money order, made payable to the Director of the United States
Geological Survey, or in currency — the exact amount. Correspondence relating to the publications
of the Survey should be addressed to
The Director,
United States Geological Survey,
Washington, D. C, June, 1S99. Washington, D. C.
[ Take this leaf out and paste the separated titles upon three of your cata-
logue cards. The first and second titles need no addition ; over the third write
that subject under which you would place the hook in your library.]
LIBRARY CATALOGUE SLIPS.
United States. Department of the interior. {U. S. geological survey.)
Department of the interior | — | Monograplis | of tlie | United
States geological snrvej' | Volume XXXIII | [Seal of the depart-
ment] I
Washington | government printing office | 1899
Second title: United States geological survey | Charles D.
Walcott, director | — | Geology | of the | Narragansett basin |
by I N. S. Shaler, J. B. Woodworth, and A. F. Foerste | [Vig-
nette] I
Washington | go\erunient printing office | 1899
i°. xx, 402 pp. 31 Jil.
Shaler (N. S.), "Woodworth (J. B.), and Foerste (A. F.)
United States geological 'survey | Charles D. "VValcott, di-
rector | — | Geology | of the | Karragansett basin | by | N. S. i
Shaler, J. B. Woodworth, and A. F. Foerste | [Vignette] |
Washington | government printing office | 1899
4P. XX, 402 pp. 31 pi.
[United States. Department of ttie interior. {TT. S. geological survei/.)
Monograph XXXIII.] •
1
i
United States geological survey | Charles D. Walcott, di- |
rector | — | Geology | of the | Narragansett basin 1 by | K. S. '
Shaler, J. B. Woodworth, and A. F. Foerste | [Vignette] |
Washington | government printing office | 1899
i°. xvii, 402 pp. 31 pi.
[United States. Dejmrtment of the intcHor. [U. *S.
Monograph XXXni.]
77G2 230
iJifiDINS CO "
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