< . a Ts RRNA ER ESSN Gy Yy YY Y; Y yi WXHV \ . VW ANC ~~ MOQ SN S SS RAH ~~ \ SS SS \N ~ YU Y Z YH Yy tii SANS NNN ES EET RRR ERRORS BINS N d e . 3 RSS QVQAIAY SN Per Kee e* ‘New York State Education Department NEW YORK STATE MUSEUM 64th ANNUAL REPORT 1Q10 In 2 volumes VOLUME 2 APPENDIXES 1 (continued), 2-5 ‘( y, eZ Tionat mus! sEUN ee TRANSMITTED TO THE LEGISLATURE Lee 20.) 1901 ALBANY UNIVERSITY OF THE STATE OF NEW YORK IQi2 STATE OF NEW YORK EDUCATION DEPARTMENT Regents of the University With years when terms expire 1913 WHITELAW Reip M.A. LL.D. D.C.L. Chancellor New York I9gi7 ST CLraIR McKetway M.A. LL.D. Vice Chancellor Brooklyn tg1g DanieEL BeacH Ph.D. LL.D. - —------- Watkins 1914 Puiny T. Sexton LL.B. LL.D. - —------ Palmyra tg12 T. GuItForD SmiTH M.A. C.E. LL.D. - -— - - - Buffalo IgI5 ALBERT VANDER VEER M.D. M.A. Ph.D. LL.D. Albany 1922 CHESTER S. Lorp M.A. LL.D. - - - ----- New York 1918 WittiamM NottincHamM M.A. Ph.D. LL.D. — — Syracuse 1920 EuGENE A. Puitpin LL.B. LL.D. -— - - - - - New York 1916 Lucian L. SHEDDEN LL.B. LL.D. - - - - - - Plattsburg 1921 Francis M. CARPENTER — — — — —--—--—----— Mount Kisco NOP eeu IIe cos IE Je, = = === eS SH New York Commissioner of Education ANDREW S. Draper LL.B. LL.D. Assistant Commissioners Aucustus S. Downine M.A. Pd.D. LL.D. First Assistant CHARLES F. WHEELOCK B.S. LL.D. Second Assistant THoomas E. FINEGAN M.A. Pd.D. Tlurd Assistant Director of State Library James I. WveEr, Jr, M.L.S. Director of Science and State Museum Joon M. CrarKxe Ph.D. D.Sc. LL.D. Chiefs of Divisions Administration, GEORGE M. Wirey M.A. Attendance, JAMES D. SULLIVAN Educational Extension, WILLIAM R. Eastman M.A. M.L.S. Examinations, HARLAN H. Horner B.A. Inspections, FRANK H. Woop M.A. Law, FRANK B. GILBERT B.A. Library School, FRANK K. WALTER M.A. School Libraries, CHARLES E. Fircu L.H.D. Statistics, Hiram C. Case Visual Instruction, ALFRED W. ABRAMS Ph.B. Vocational Schools, ARTHUR D. DEAN B.S. Se ales: -N Wi NV2z2. Se or New York No. 55 EN SENATE ANU AR zon one 64th ANNUAL REPORT OF THE NEW YORK STATE MUSEUM VOLUME 2 To the Legislature of the State of New York We have the honor to submit herewith, pursuant to law, as the 64th Annual Report of the New York State Museum, the report of the Director, including the reports of the State Geologist and State Paleontologist, and the reports of the State Entomologist and the State Botanist, with appendixes. St Crain McKetway Vice Chancellor of the University ANDREW S. DRAPER Commissioner of Education 148 Appendix 1 (continued) Geology Museum Bulletins 148, 152, 153, 154 Geology of the Poughkeepsie Quadrangle Geology of the Honeoye-Wayland Quadrangles Geology of the Broadalbin Quadrangle, Fulton-Saratoga Counties, New York Glacial Geology of the Schenectady Quadrangle Education Department Bulletin Published fortnightly by the University of the State of New York Entered as second-class matter June 24, 1908, at the Post Office at Albany, N. Y., under the act of July 16, 1894 No. 492 MEAIB VAIN NEA ING NCE APRIL I, IQII New York State Museum Joun M. CLARKE, Director Museum Bulletin 148 GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE BY C.E. GORDON PAGE PAGE MimMEROGMCHON: ..: +c k enim oe cee 5 | The Wappinger creek belt....... 48 Location and other general features die wishkall@imestones.- esse ee 70 of the quadrangle............. 6 | The ‘Hudson River”’ slate group 82 Topography .............-.0.00% 7 | Preglacial history of the drainage 96 WAM AC Cree see ais ck syaees WW Sects. el | (Saal geologyic ies. hy ieee 99 General geology................. 9 | Retreat of the ice sheet...... Dee ATOO pices Becloele werk Ginna 4 7° | Postglacial erosion.............. 104 fevoee nse aie 0 in | Tnewiecentidepescon | a) 105 The Hortontown basic eruptive Other drainage featuresand adjust- and associated metamorphic TITOINGS ics lovateneucn evens Gieolohekeearece eter 105 Re ee cd es WT Ah 37 Land forms A a rascal ce ae a area 105 The basal quartzite (Poughquag) 39 | Economic geology............... 106 The Wappinger (Barnegate) lime- Bibliography.) cane ee I1O UOMO Myr ceata ay otal uacotead ab. simiss Holes vod ial 6 0X6 (=> Saaremaa RE A aux Giceorh Gy ashy 117 ‘ ie ‘+ ay ; i. re " * i & - 4. . - ‘ . . saa 8 ‘ om : F a é Hi € i br Pu a % i i) . OD * aed i) i i Bir MD AS ate iets ; 7 Yr, : Camry? Re # ; ae ae ‘o, a Ac ¥ i iy J S4 i U 7 - ; mh ry ‘ eine ROR co ca ae ce a 7 Ai a, ol ah 7 neat ey acne 7 ¥ 7 New York State Education Department Science Division, November 5, 1910 onmAndrew S Draper LL. D. Commussioner of Education Dear sir: I beg to transmit to you herewith a manuscript en- titled The Geology of the Poughkeepsie Quadrangle, accompanied by a geological map which has been prepared under my direction by Professor Clarence E. Gordon. The work has been executed with circumspection and accuracy and I recommend the publication of the matter transmitted, in the form of a bulletin of this Division. Respectfully Joun M. CLaRKE Director STATE OF NEW YORK EDUCATION DEPARTMENT COMMISSIONER'S ROOM Approved for publication this 7th day of November 1910 Commissioner of Education ~, Education Department Bulletin Published fortnightly by the University of the State of New York Entered as second-class matter June 24, 1908, at the Post Office at Albany, N. Y., under the act of July 16, 1894 No. 492 Ae BAIN RON] axe APRiLy I) 19nT New York State Museum JoHn M. Crarke, Director Museum Bulletin 148 GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE BY CLARENCE E. GORDON INTRODUCTION The preparation of this paper was begun at the suggestion of Professor J. F. Kemp. The field work was carried on at intervals during the summers of 1906—7-8-9. During the intervening win- ters the extensive literature dealing with the geology of eastern New York State, western New England and the areas of similar rocks at the south was read with care. A preliminary map of the quadrangle was prepared by a sum- mer school party of Columbia University at work for a week under the direction of Professor Kemp, Professor A. W. Grabau and Dr C. P. Berkey. This was of great assistance in the field. ‘i The writer owes much to Professor Kemp for kindly criticism. Dr Charles P. Berkey has offered important suggestions. Par- ticular thanks are due Professor John M. Clarke for a generous interest which has made some of the field work easier of execution. 6 NEW YORK STATE MUSEUM LOCATION AND OTHER GENERAL FEATURES OF THE QUADRANGLE The Poughkeepsie quadrangle lies in the Hudson river valley about midway between New York city and Albany. It falls between parallels 41° 30’ and 41° 45’ north latitude and meridians 73° 45 and 74° oo’ east longtitude, and is therefore 175 emiles long by about 13.2 miles wide. It embraces an area of about 230 square miles. The Hudson river crosses the quadrangle from north to south near the western boundary. The river is slightly deflected to the west at New Hamburg and forms the quadrangle boundary at the southwest corner. The larger portion of the area lies east of the Hudson in the southwestern part of Dutchess county. At the very southeast corner is a triangular bit of the township of Kent in Putnam county. West of the river is a strip of Ulster county and a block from the northeastern portion of Orange county. Poughkeepsie, the county seat, is a city of about 25,000 inhabit- ants. Wappinger Falls on Wappinger creek, Matteawan on Fish- kill creek and Fishkill Landing on the Hudson, opposite New- burgh, are important villages. Wappinger Falls and Matteawan are manufacturing towns and each owes its size and importance to the stream on which it is located. East of the Hudson the region 1s chiefly a farming country and is well adapted to tillage, grazing and fruit growing. West of the river the topography, soil and drainage are peculiarly adapted to the growing of fruit, for which the proximity of the river affords excellent climatic conditions. Dutchess county was settled very early in the history of the State. The country is attractive. It is easy to imagine that im- migrants voyaging up the Hudson through the inhospitable region of the Highlands would have been attracted by the stretches of open country which lay north of the rugged mountains. The quadrangle is easy of access. Boats plying between New York and Albany stop at Newburgh and Poughkeepsie. The New York Central and West Shore lines, connecting with Albany and the West, follow the banks of the Hudson. The former joins with the Newburgh, Dutchess and Connecticut division of the Central New England at Dutchess Junction and Fishkill Landing, and at Poughkeepsie with the main line division of that road. At Pough- keepsie it also crosses the Highland division of the New York, tie a SCALE OF MILES (as Be Se) a 40 20 75° (pie Fig. 1 Sketch map showing location of Poughkeepsie quadrangle GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE vy, New Haven and Hartford. Ferries cross between Fishkill Land- ing and Newburgh and between Poughkeepsie and Highland on the West Shore Railroad. NOP OGRARENY East of the Hudson the topography is chiefly that of a rolling upland of moderate elevation, which is due in part to the nature and structure of the underlying rock formations as affected by erosion, and in part to the mantle of glacial deposits. Along the southern margin of the quadrangle are several rugged spurs of the Highlands. These are bold, often precipitous, and usually wooded. They are known as the Fishkill mountains, receiv- ing their name from old Fishkill township, of which they are a part. These mountains are made up chiefly of Precambric gneisses and are flanked by and faulted with the Paleozoics of the valley. The westernmost Highland spur is the northern extension of Breakneck mountain ridge and the part within this quadrangle is known as Bald hill (see plate 1). It has a maximum elevation of 1540 feet. The Mount Honness spur next east has an elevation of 840 feet at its northern extremity, Mount Honness proper, but © reaches a height of 1300 feet near the quadrangle boundary (see plate 2). A short spur east of Honness, with an elevation of 885 feet, separates it from Shenandoah mountain, which has a maximum height of 1115 feet. East of Shenandoah mountain the Highland mass attains an elevation of 1232 feet at “ Looking Rock,” which is at the summit of the steep northwestern slope. This spot is widely known because of its fine view. North of the Fishkill mountains the rocks within the quadrangle are principally shales, slates, grits, phyllites and limestones. ‘The more metamorphic character of these strata as they are followed eastward from the Hudson finds expression in the higher elevation of the slate and graywacke in the northeastern part of the area. Here the hills in places reach a height between 700 and 800 feet. West of the Hudson the average elevation in the slates and grits is greater than on the east of the river, often attaining 400 to 600 feet. “Illinois mountain,’ the northern extremity of Marlbor- ough mountain, is 1105 feet high. In contrast to the heights is the gorge of the Hudson, which borings have shown reaches a depth near Storm King of over 700 feet. 19,0) NEW YORK STATE MUSEUM DRAINAGE The Hudson river is the dominating factor in the drainage of this area. ‘The principal tributaries of the master river within this quadrangle come in from the east. The most important are Wappinger and Fishkill creeks; of lesser importance are Casper and Fallkill creeks. Wappinger creek has its source near Pine Plains, some 16 or 17 miles northeast of Pleasant Valley, on the southwest of a narrow divide that separates its headwaters from the valley of Shekomeko creek. It has a general southwest course along a narrow limestone belt, and finally enters the Hudson at New Hamburg. At present it bears away somewhat from the limestone along its lower reaches and flows across the slates, over which it cascades gently in several places. At Wappinger Falls it makes a descent of about 60 feet over the slates, and from this village to the Hudson, a distance of about two miles, it occupies a drowned valley. It receives a few small tributaries within the quadrangle, the largest of which drains the slates southeast of Wappinger Falls and empties into the main stream below the village. Wappinger creek furnishes power at Pleasant Valley, near Titus- ville, and at Wappinger Falls, and formerly was utilized at Rochdale. Fishkill creek is a somewhat larger stream and has a greater watershed. It also drains a large part of the area just to the east, where the main stream has its source on the western slope of Chestnut ridge, a high mass of schist separating the Clove and Dover-Pawling valleys. East of the quadrangle it receives an important tributary with its source in Whaley pond. Sylvan lake sends a small tributary into this stream near the eastern edge of the quadrangle. Several good-sized brocks join the main stream from the north. Of these Whortlekill creek is a small brook which enters the quad- rangle just east of Arthursburg, about a mile from its source. It joins the Fishkill about a mile south of Hopewell Junction. Jack- son and Sprout creeks are larger. The former drains the western slope of the ridge between Lagrangeville and the Clove valley, while the headwaters of Sprout creek extend to the narrow ridge northeast of Verbank, whose eastern slopes drain into the Dover- Pawling valley. Sprout and Jackson creeks join north of Fishkill Plains and the stream formed by their union flows into Fishkill creek, two miles north of Brinckerhoff. Plate 1 ture, as seen from Mount Beacon 1C t of the pi he left hal in ¢ f Bald hill, shown i 1ew O ° = } A Jodoid ssouuo py JUNOW St sinjord 9y1 Jo 4yoy °Y} HO s.usUTID ayy, “weYyUaTy JO dSPT[IA ay} Ieau WOT uaes se ‘SUIEJUNOW []IYYSIy oy} Jo Inds SSouUO FT JUNOT Yi Jo Mara Z aed a GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 9 Several brooks which drain the northern slopes of the Fishkill mountains and the valleys between them join Fishkill creek from the south. Of these, the largest are those leaving the Highlands through Shenandoah hollow and the valley of East Fishkill Hook, and “Clove creek” south of Fishkill Village. Fishkill creek fur- nishes power at Hopewell, Brinckerhoff and Matteawan. Casper creek rises near the northern boundary and flows south- west in a rather wide valley to the Hudson which it joins two and one-half miles north of New Hamburg. Fallkill creek drains a large area to the north. It flows in a general southwest course to Poughkeepsie where it turns on itself, and, making a large loop, flows north for one-half of a mile and then west to join the Hudson. Several brooks, but none of any size, drain the slopes on the west of the Hudson. There are no. natural lakes or ponds of conspicuous size within the quadrangle. Those of any consequence apparently date from the time Of the retreat of the ice sheet from this region. GENERAL GEOLOGY ~The Fishkill mountains belong to the Highlands province of Pre- cambric rocks. ‘These have their greatest development in Putnam county just to the south. The spurs that have been mentioned are the northern terminations of ridges of gneisses which have a general northeast-southwest trend. Above Peekskill these gneisses are continued across the Hudson into New Jersey. Eastward they extend into Connecticut. The summits of the Fishkill mountains, with those of neighbor- ing ones at the south, present a fairly even sky line which may be followed northeastward along the crests of the ridges of the younger rocks. This general uniformity’ of level is believed by many to mark a former peneplain in this region toward the close of Cretacic time (see plate 3). North of the Fishkill mountains are the younger rocks of the area. In general, these do not now tend to climb far up the flanks of the older masses. In most cases the two are faulted against each other and the rocks of the mountains reach close to their bases. In a few places the younger strata extend up a moderate distance on the older rocks and are disturbed relatively little. These younger strata rest unconformably upon the Precambric. They are the southwestward representatives of the rocks of western Massachusetts and Vermont and are now known to include strata 10 NEW YORK STATE MUSEUM which range in time from the base of the Paleozoic to the upper part of the Ordovicic period. Northeastward these rocks extend into Massachusetts and Vermont and southwestward into New Jersey, Pennsylvania and beyond. Within the quadrangle they are of considerably lower average elevation than the gneisses of the mountains. This reduced eleva- tion is believed to represent the erosion that has taken place in these rocks below the Cretacic level after the peneplain had been elevated at the close of Cretacic time. So far as now known, these younger strata have no later rocks older than the Quaternary overlying them within the limits of the quadrangle. PREVIOUS GEOLOGIC WORK Because of the extensive geographic development of these rocks and their difficult geology there has appeared, during the last fifty years or more, a large body of literature dealing with them through- out their length and breadth. The work has been carried on under the auspices of State and federal surveys and by private enterprise. Work within this quadrangle was undertaken early in the history of serious geological investigation in this country. In 1843 W. W. Mather submitted his quarto report on the Geology of the First District of the State of New York. This dealt with southeastern New York and was the first important contribu- tion bearing on the geology of this area. With the exception, per- haps, of an excursion by Sir William Logan and James Hall in 1864, which resulted in the assignment of the younger rocks of this and neighboring areas to Logan’s Quebec Group, and which introduced much confusion at the time, no other important contribution was made until 1878. In that year T. Nelson Dale discovered fossils in the slates at Poughkeepsie. The fossils were assigned by Hall to the “ Hudson River Group.” The find attracted the attention of Professor J. D. Dana to the strata of southern Dutchess county. This eminent geologist, what the time was working at the difficult stratigraphy of western Massachusetts and the neighboring portion of New York State, now traced the limestones from the north to the Hud- son river, discovered fossils in them at Pleasant Valley, and dis- cussed their general geologic significance. Apparently through the influence and encouragement of Dana, Professor W. B. Dwight began his fruitful investigations in the Wappinger limestones of Dutchess county. Professor Dwight’s papers were published at intervals from 1879 to 1900. His investi- ooUvISIP 94} UL dInjord dy} Jo JYSI4 oy} UO UMOYs st Bury WIOJS JO IWOp Pepunos oy T, “ule;dauod ‘UIRJUNOW YuYVaIG Suoje PteMjsomyjnos UoOoveg JUNO WOT, MaIA VY IPT) PIJIISStP 9Y} SUIMOYS “IOALL uOspnyy 9y} Ssoroe € 331d GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 1 bal f gations greatly extended our knowledge regarding the age of the Wappinger limestones, particularly those of the Wappinger creek belt. In 1886 J. C. Smock, as a part of a preliminary report on the Pre- cambric rocks of the Highlands east of the Hudson, discussed the gneisses of the Fishkill mountains. But notwithstanding these con- tributions, the areal geology has not been mapped in detail up to the present time. St kAriGhAPrIG AE al Bins SEDIMENTARY PERIODS sO ERUPTIVES Formations Terranes Alluvium Recent Quaternary Terraces : Kames Glacial Drumlins (Unconformity) ‘“Hudson River’’ slates, B grits and phyllites Utica? Trenton Ordovicic Wappinger limestones and| Trenton dolomites, in part (Disconformity) Beekmantown —————————_—___———| Hortontown hornblende (Disconformity ?) rock Cambric Wappinger limestones and! Potsdam -dolomites, in part yeas Georgian Poughquag quartzite Georgian (Unconformity) ; Gneisses of the Fishkill Shenandoah granite Precambric mountains and inliers of| ‘‘ Grenville ”’ Bald Hill granite gneiss these rocks tlt RC RIC GNETS Sas DISTRIBUTION Within the Fishkill mountains the boundary of these rocks, as shown by the map, follows closely the lower contour lines of the spurs. The Glenham belt is an inlier of these rocks. It has the same trend as the ridges of the gneisses in the Highlands and extends as a narrow strip from a point just north of the carpet mill at Glenham northeastward to “ Vly mountain.” 1The hill marked Fly mountain on the map is just southeast of what, in this vicinity, is called Vly mountain, corrupted to Fly mountain. The swamp just south of the eminence doubtless suggested the name (Vly- swamp). [2 NEW YORK STATE MUSEUM South of the Glenham belt, in the town of Matteawan, are two smaller inliers of the gneisses connecting the Glenham belt with the Highlands. Between the rocks of the Highlands and those composing the masses of inliers there are some differences which help to throw light on the history of both. There are also marked resemblances which apparently serve to clinch their relationship. PROBLEM OF THE GNEISSES The study of the gneisses speedily develops very puzzling prob- lems, which in all cases may not admit of satisfactory solution. In some way these rocks must express the several successive changes which they have experienced. A complex history is suggested, but all its events are not easy to trace. PROMINENT STRUCTURAL FEATURES The most impressive feature of the gneisses is the northeast- southwest alignment of the ridges which constitute their outcrop. Between the ridges are parallel longitudinal valleys. From the published descriptions, these features, with some exceptions, seem to hold for the entire Highlands and to extend southward into West- chester county. The gneisses are uniformly banded or foliated throughout their entire breadth from west to east, and the strike of the foliations in general follows the trend of the ridges. In a few places only does the foliation approximate schistosity in any degree. Over most of the area there is an easily distinguishable arrange- ment in parallel stratalike masses which also follow the topo- graphic features. These do not show an orderly repetition, though masses of very similar mineralogy are irregularly repeated. Occa- sionally more massive types occur, but these, too, seem to follow the structural features just mentioned. The prevailing dip of the folia- tion planes to the southeast imparts a strongly isoclinal character. The ridges clearly date from Postcambric time. It seems rea- sonable to infer that the other structural features just outlined have a common origin and belong to an earlier epoch. There is much evidence of extensive faulting which is developed chiefly, or at least most prominently, along the strike. Such faulting might easily account for the lack of orderly repetition of character- istic rock types. Most of this faulting belongs to the disturbance GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 13 that produced the ridges. The gneisses clearly show the effects of repeated orogenic disturbances. In some places it is clear, from the position and structure of the overlying younger rocks, that most of the features of the gneisses date from Precambric time. Where the relationship of the basal quartzite to the underlying gneiss is most plainly seen, as in the West Fishkill Hook,' the latter stands at a high angle with a uniformly northeast-southwest strike, while the quartzite dips at a low angle with varying strike. In other places the discordance between the dips and strikes is plainly discernible. The quartzite has been folded relatively little in many places, and never within this quadrangle to the extent shown by the gneisses. Faulting, instead of extreme folding, occurred in connection with Postcambric movements within the gneisses. The early crystalline condition of the gneisses would have favored faulting and shearing and would have prevented much later folding within them. It is certain that the isoclinal character is of Pre- cambric age. It seems possible, therefore, in a large way, to apportion the structural features of these gneisses as seen in the field among Oro%ene movements of Precambric and later time. It is quite uncertain how many different disturbances may have occurred in Precambric time and whether all the later structural features are of similar age. The lines of foliation, as seen in outcrops, are usually rectilinear. When wavy, they are only slightly so. This latter feature seemed most noticeable on Shenandoah mountain. Crinkling is rare. Two or three instances of it were noted in the Glenham belt. Jointing is common and frequently gives the appearance of thick exfoliation. Faults are divisible into two kinds, reversed and normal. It seems most likely that the normal faults followed the compression that produced the thrusts and are therefore of the nature of adjust- ments. All the faults that have been noted appear to belong to the great mountain building process of Ordovicic time which elevated the Paleozoics of the Green mountain belt. This is indicated by the relations which exist between the younger and older rocks and by the fact that the fault lines of the mountains are projected north- 1 The recesses east and west of the short spur that separates Mount Honness from Shenandoah mountain are respectively known as East and West Fishkill Hook. I4 NEW YORK STATE MUSEUM ward into the younger strata, where they show features that leave their age unmistakable. Doubtless in some cases what now appear to be reversed faults of moderate displacement within the gneisses, or along contacts, are truncated thrusts of large size. This inference is borne out by the presence of large thrusts in the Paleozoics at the north. It would appear that not only did distinct normal fault breaks occur as the result of adjustments following the elevation of the Green mountains, but that normal slips occurred along the planes of the earlier thrusts. | This feature is best shown in the relations now existing between Bald hill and the Mount Honness spur, and in similar ones between Shenandoah mountain and the mass of gneiss at the east of it. In these two instances the Paleozoics have clearly been dropped back between the gneiss spurs with a large throw on the west, marked in one case by the scarp on the east of Bald hill, and in the other by that on the east of Shenandoah mountain. The two spurs in each case tended to act as a single block. The normal fault intersects the thrust at an acute angle forming a tri- angular valley narrowing southward. Some backward movement along the thrust plane must have accompanied the slump. Dimin- ishing tension faulting eastward is marked by small scarps on the west of the Honness spur but is not noticeable on the eastern gneiss mass. The Hook spur shows these features imperfectly developed. PETROGRAPHY- General. The gneisses show much similarity in their mineralogy. Distinctive characters are furnished by the structure, the preponder- ance of some minerals, or the degree of alteration in the rock. A few composite types may thus be defined. It will be convenient to describe these first, while the variations in many instances may best be indicated in discussing their outcrops. The thin sections may be reviewed as a whole later. Possible ancient surface altera- tions must always be carried in mind. Bald hill granite gneiss. This rock is prominently developed within and south of the quadrangle. There is great uniformity in its general color, mineralogy and texture. It shows a few variations, but as a whole is remarkably homogeneous. In outcrops it is com- monly drab colored and granitelike in appearance. The thin sec- GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE I5 tion of the usual variety shows quartz in large and small anhedrons. Orthoclase and plagioclase are abundant, with the former slightly imymexcessy -s Dinene 1s some microcline and hornblende is plentiful. Irregular. grains of magnetite are frequent. There are a few. scat- tered zircons. In some instances, even where the hand specimen appears rather massive, the thin sec- tion shows a stringer- like arrangement of the hornblende (see figure 2 oe te magnetite 1s often hydrated, giving Fig. 2 Bald hill granite gneiss. Actual size 3 mm. Q, fy . z Bent. O, orthoclase; P, plagioclase; H, hornblende; surface exposures a black, magnetite rusty color. The principal variation is a rock of coarser texture, with. the mineralogy of a diorite. It shows hornblende, abundant plagioclase and a very little quartz (see figure 3). In one case where the FOCk - was extremely fresh the magnetite formed a perfect pseu- domorph after the am- phibole and was abund- ant in the section, while the hornblende was greatly bleached. Minere 1s utter lack of evidence to show that the rock has undergone a complete change from an earlier condition. It would seem that, so far as the rock has just been Fig. 3 Diorite variation of the Bald hill gneiss. Actual dicencced aie GS miner- size 3mm. P, plagioclase; H, hornblende; Q, quartz alogy and texture, we are dealing with primary features. On the whole, the sections indicate a rock of plutonic habit which took on a gneissic character and underwent certain other changes at the time Loe NEW YORK STATE MUSEUM of its formation. The gneissic character is best regarded as primary, justifying the use of the term gneissoid granite to qualify the name granite gneiss. The restlessness of the magma at the time the minerals were forming seems to find expression in the stringerlike arrangement of the hornblendes and in parallelly arranged pellets of quartz occur- ring in the feldspars, which do not appear to be secondary and of later introduction. ‘hese features, with the rounded character and smaller size of some of the grains and the absence of micropegma- titic intergrowth, point to conditions hampering crystal formation. The thin sections also show certain dynamic effects of later date, in common with all the gneisses of these mountains, in the form of strain phenomena of different kinds. There are one or two instances of comparative freedom from such in which the quartz always gives sharp, decisive extinction and in which prominent cracks and bent lamellae are absent. Hornblende gneisses. ‘The outcrops of these rocks are much alike and the thin sections which have been examined agree very closely. Exposures are dark in color. The essential minerals are chiefly plagioclase and hornblende, with some quartz and a little orthoclase. Magnetite is rather common as irregularly-shaped par- ticles, or as “dusts: Zircons are occasional. Some sections show biotite in addition ‘to hornblende, but the for- ies 3 mer is decidedly subor- WE A dinate and usually has Zs sil every appearance of Bilsing being secondary. It ap- VA 5 yi: ap a, parently belongs to that period of metamorph- ism which more usually found expression in strain phenomena of different kinds but which sometimes _ re- Fig. Sketch of a hornblende gneiss. Actual size 3 mm. : a! ‘; MOS atete P, plagioclase; H, hornblende; black, mag- sulted in new minerals re among the “ primary ” ones, especially in those cases where the rock had previously been exposed to unusual alteration. The feldspars also frequently show evidence of former decay. The indurated and general compact GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE iy, condition indicates that the alteration is an ancient character. Fig- ure 4 gives a sketch of a thin section of typical hornblende gneiss. val aN AS Fig. 5 Sketch ofa micaceous gneiss. BS QO, quartz; O, orthoclase; P, plagioclase; B, biotite Actual size 3 mm. Micaceous gneisses. diineses may. sve passed Ovetue Didehy.) Fle xcepe that biotite plays the role of hornblende, they are very similar in their mineralogy. In some cases magnetite is asso- ciated with a mineral whose identity is lost or obscured. The thin sec- tions often suggest that the prominent biotite is secondary and in these cases the outlines of an- other mineral, possibly. hornblende; “may~ © be faintly traced. In these instances it is possible that the biotitic gneiss was first a hornblende rock and that it was subjected to more than usual alteration before recrystallization. Microcline is rather abundant. Biotite oc- curs abundantly as a “primary ’’ mineral in- dependent of ‘horn- blende. Sometimes these gneisses show much quartz and are finegrained, strongly suggesting altered sedi- ments. Shenandoah moun- tain granite. A coarse, white granite made up almost entirely of quartz and feldspar was noted on Shenandoah Fig. 6 Shenandoah mountain granite. Actual size 3 mm. Q, quartz; O. orthoclase; P, plagioclase; M, microcline; Mu, muscovite mountain at the summit of the steep northwestern slope, along the road from the East Hook to Hortontown. It is very massive in 18 NEW YORK STATE MUSEUM appearance in the ledge and hand specimen. The thin section shows quartz, orthoclase, microcline and plagioclase. A few small and scattered flakes of muscovite, which is probably a primary min- eral, are present. Microcline is abundant. There is a tendency to microperthitic intergrowth of plagioclase and orthoclase. It has the earmarks of a plutonic rock and bears little evidence of eneissoid structure, so that if it is of Precambric age it must be thought of as having escaped any pronounced foliation. This seems remarkable, considering the prominence of foliation in the gneissic series. The effects of dynamic metamorphism are chiefly in the form of strain shadows in the quartzes. Glenham gneiss. The prevailing and characteristic surface rock of the Glenham belt 1s a granitic gneiss. It appears to be an altered derivative of other gneisses which are entirely similar to those of the Highlands, and which are exposed in places within the belt. The surface gneiss is foliated in certain por- tions, while in others it is massive. «There ganre , minor variations in tex- SC \ ture and in mineralogy MESS which depend upon both an ancient and a more recent alteration. These varieties grade into one another. The gneiss is usually red from dis- seminated iron stains and over much of the belt is deeply chlorit- ized. Fig. 7 Glenham gneiss. Actual size 3 mm. Q, quartz; ! : 5 M, microcline; P, plagioclase; CB, chlorite after biotite, The thin section gts ae shows abundant quartz with orthoclase, microcline, plagioclase, and biotite altered to chlor- ite. Magnetite is abundant and zircons are occasional. Occasionally the rock consists of feldspar and quartz with very little or no mica. OUTCROP .OF THE BISHRILE, MOUNTAIN: GNEISSES Matteawan. Gneisses which can be readily traced into those of the Fishkill mountains outcrop near their base in the eastern part aS Ge bag: es as « a ae “~~ eo at nt 6 LEGEND if | i : | | ( | Xu + 8 a ot « ” GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 19 of the town of Matteawan. . The discussion of these may be fol- lowed by reference to the map of Matteawan (figure 8). The most western outcrop which has been noted is at the corner of Vail avenue and Washington street. The gneiss at this spot is very similar to that which composes the two inliers shown on the map at the northwest. Another outcrop occurs at the junction of Prospect and Mountain streets. A line drawn between these two outcrops marks the western boundary of the gneisses of the mountains, so far as they can be followed by actual outcrops. East of Washington street along Prospect, Union, Robinson and Alice thoroughfares and along Green, Park, Duncan and Goodrich side Smeets OuLcEops are mumerous. North of Mountain street the gneisses pass beneath the drift. A quarter of a mile to the north- east they are exposed again in the gorge of Mount Beacon brook. The reddish and greenish colors, characteristic of the Glenham belt and the inliers farther west, and frequent epidotic gneiss, were noted among the surface exposures of the gneisses just described. Other- wise these exposures are similar to the rocks in the Mount Beacon brook section. Mount Beacon brook section. Above and for a short distance below the bridge on Mountain street, near the foot of the mountain road, the brook has cut an interesting section in the gneisses. Just above the bridge the foliation and “ bedding” planes strike n. 54° e. an@uaipeabout 75 s.e. Below the bridge the strike varies be- tween this angle and 69° e. of north. The rocks in this section show an isoclinal arrangement in “ beds ” with high dip to the south- dst. Below the bridge, the lowest portion of the section involves some forty feet of dark hornblendic gneiss. This rock is banded, though in places for the width of several inches it is massive. When water- worm, such surfaces present a spangled appearance. This “stratum” is abruptly succeeded by a lighter colored one of much less uniformity of appearance. It is made up of imperfect alter- nations of granitic, quartzitic and composite “ beds,’ which vary in thickness from the width of an inch or less to two feet. Some “beds” show light and darker bands. Others are uniformly light colored, often with little or no trace of a ferromagnesian constitu- ent, ~Uhis stratum’ continues up stream for a hundred feet or more and passes beneath the bridge. It is succeeded by the Bald hill gneiss with varieties that strongly resemble the rocks of the Glenham belt and the Matteawan inliers in texture and mineralogy. 20 NEW YORK STATE MUSEUM In the upper portion of the gorge above the bridge the north wall for some distance is a rusty, pinkish rock of fine grain and rather massive appearance. It resembles certain phases of the basal quartz- ite which have been noted outside the quadrangle, particularly the outcrops in the brook crossed by the mountain road a mile south of Dutchess Junction. This rock is jointed, and rests upon the gran- itic derivative of the Bald hill gneiss. Bald hill. The rock composing this spur of the Highlands was carefully examined along its base while tracing the quartzite, and also in two sections across its summit from west to east. One of these sections was made across the northern portion of the spur along an old wood road leading from the lane southeast of the Maddock farm near Glenham station. The other was taken partly along the road ascending Mount Beacon, then bearing to the left past the Graham place through “ Hell Hollow ” to the Cold Spring road. The rocks in the quarries near Mount Beacon reservoir, and in the excavations made for the new house at the summit of Beacon during the summer of 1908, as well as the section along the road descending from the reservoir to Matteawan, were studied. Com- parisons were made with the outcrops along the base of the ridge to the quarry at Storm King station and in the railroad cuts from Storm King to Cold Spring. An examination of other parts of the ridge of which Bald hill is the northern extremity, was necessary in order to form a clear idea of the character of the gneiss. Along the northwestern slope of the spur the gneiss is mainly a medium-grained, laminated hornblende rock with some micaceous variations. Along the basal portion of this slope the gneiss is usually rusty from included iron stains. Higher up it is commonly a drab or gray rock. The laminated character is more noticeable and the laminations are finer along the basal portion of the northwestern slope. Throughout most of the mountain the gneiss is rather coarsely or indistinctly foliated and in places is quite massive and granitic in appearance. The characteristic rock of Bald hill, as just described, is identical in texture and mineralogy with the rock in the quarry at Storm King station and with the prevailing type in the railroad cuts be- tween Storm King and Cold Spring. It is the chief variety in the quarries at Mount Beacon reservoir. At the excavations for the new mountain house on Beacon, the drab-colored granitic gneiss passed into a variety composed of white feldspar and hornblende. In the hollow between Beacon GEOLOGY OF THE POUGHKEEPSIE ‘OUADRANGLE 21 and Bald hills, along the road descending from the reservoir, the granitic hornblende rock is often very dark in color, which cor- responds with a greater freshness in the rock. The presence of cccasional micaceous variations has been noted. They are apparently confined to the more finely laminated portions of the gneiss and there is reason for thinking that the mica is secondary. The thin sections show abundant disseminated mag- netite which has become hydrated in many places, giving surface exposures a rusty color. | The hcemogeneous character of the Bald hill granite gneiss is noteworthy. In areal extent, it covers about eleven square miles east of the Hudson. The general igneous character of the rock is very impressive. The varieties that have been described would appear to be explainable as normal variations from a common magma. Mincenock is certainly. of Precambric age. By its’ form and isolation it Coes not appear to have the character of a basal mem- ber. JI have been unable to discover any other type which could reasonably be referred to this gneiss. If a basal formation, it should be of more frequent occurrence in these greatly eroded rocks. It therefore does not appear to be older than the other gneisses. All evidence of a possible unconformity would have been com- pletely obliterated. If contemporaneous with the other gneisses, on the assumption that they are sedimentary and that it is igneous and having the character of a sill, it should then occur also in other places to the east. It might be a laccolith, in which case it might have furnished the initial bulge at the time of folding. The more strongly banded character of the gneiss along the margin and the somewhat massive central portions might permit the interpretation of anticlinal structure. The pronounced alignment which this granite has with the other gneisses favors the view that it was thrust up into the gneisses at the time of their folding. All possible exomorphic and endomorphic effects would have been neutralized by the agencies of regional metamorphism. In addition to its other characters, the thickness of this formation is opposed to the idea that it is of sedimentary origin. The Mount Honness spur. A short distance east of the Cold Spring road in the hollow between this spur and Bald hill the rock resembles the Bald hill gneiss. In some places it is granitelike, 22 NEW YORK STATE MUSEUM coarse-grained and only slightly foliated, looking like an altered de- rivative of the gneisses. The fault that borders Bald hill on the east may be within the Bald hill gneiss for a distance. North along the road toward Fishkill Village the rock becomes more foliated. A thin section of this variety shows some biotite in addition to hornblende, but the former is decidedly subordinate and is apparently secondary. Two mountain roads over this spur from the Cold Spring road to West Fishkill Hook give fair sections. There are also numer- ous outcrops in the fields to the north and south. Surface exposures are confusing both as to structure and petrographic characters. In some places the gneiss apparently dips to the northwest at low angles, but where the foliation planes may be detected, they dip to the southeast at high angles. The rock often has a granular and hybrid character that seems best interpreted as the condition resulting from the induration of a partially disintegrated rock which is pri- marily a very ancient character. The apparent northwest dip is accordingly best explained as a sort of exfoliation between the basal eneiss and the altered surface derivative. On the whole, the section is across a series of “strata” showing tendency to definite alignment with each other and to variety of composition. In the main the rocks of this spur may be classified b as micaceous and hornblendic gneisses forming rather thick “strata,” which usually exhibit uniformity in mineralogy for some distance across the strike. The road from Brinckerhoff to Johnsville crosses this spur north of Mount Honness proper. Fine exposures have been made in the dark colored hornblende gneisses along the road in the process of constructing the new State road, and in the quarries just south of Arvis Haight’s, from which stone was removed. These sections show thick masses of the hornblende gneiss. Lighter colored eneisses have been noted interstratified with the hornblende varieties. In connection with the question of the origin of the hybrid char- acter of the gneiss along the northwestern slope of this spur it is interesting to note that the slope is gentle. Although it now lies in a faulted position against the limestone, the basal quartzite may have reposed on the gneiss along this slope subsequent to the eleva-. tion which brought the gneiss against the limestone. More distinct “ passage beds ” overlying the inclined gneiss occur just beyond the point where the two mountain roads cross on the crest of the ridge. Between the eastern fork of the roads thus GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 23 formed, west of the barn of Irving Knapp, thick masses, resem- bling both the gneisses and the quartzite in their mineralogy, dip to the north at a moderate angle. Farther along the road to the east of the house, ledges more closely resembling the quartzite were found. The woods and thick covering of drift, however, greatly obscure everything to and for a short distance beyond the west road into the mountains. South of the Carey farm, between the brook and the road, the quartzite was found grading downward imtonay hybrid rock. \ ; The Hook district. South of the quartzite slope, back of the farm of Garrett Smith, the thick woods obscure the succession in the gneisses and good outcrops are scattered. The outcrops in the field southwest of Alonzo Smith’s house (see plate 4) on the east road into the mountains and in the neighboring woods, are micaceous gneisses. Within the small space of the outcrop shown in the plate the gneiss passes from a rather coarse rock with quartz stringers through one with finer laminations into a purplish rock with still finer laminations. A comparison of the thin sections of these varieties shows a similarity as to essential “primary” minerals with biotite as the ferromagnesian constituent. The feldspar is chiefly plagioclase. Omlantez 1s abundant The degree of alteration of the primary minerals varies much. It is severe both in the feldspars and the biotite, but shows itself chiefly in Enter: lattetaae elem vlae coarser gneiss the biotite is only slightly altered, — while in the finely lami- nated purplish rock it is represented by masses of magnetite anda great abundance of finely Fig. 9 Altered micaceous gneiss from the Hook district. 2 cre eee ONC Tee iaiiciccace. piace, granular, material, prob- tit ioti O90 0 pupae es ably sericite, with only occasional traces of the boundaries of the original mineral (see figure 9). The second variety mentioned shows a gradation between the 24 NEW YORK STATE MUSEUM other two. The purplish color of the darker rock is plainly due to the abundant magnetite. Though apparently greatly decomposed, these rocks are firm and compact in the hand specimen. The magnetite is not altered into hematite or limonite. The conditions suggest that the altera- tion of these rocks dates back to an epoch preceding the deposition of the basal quartzite, which, as the proximity of this formation shows, formerly covered the gneisses, probably until glacial time. East of the east road into the mountains the quartzite has been dropped by a fault. It extends farther to the south than on the west of the road, partly on this account and partly because of a syncline at this point. No peculiar variations were noted in cross- ing the Hook spur to East Fishkill Hook. The southward exten- sion of the quartzite leaves comparatively few outcrops outside the thickly-wooded area of the spur. Shenandoah mountain.‘ Above the drift-covered slope of the quartzite, along the northwestern slope of the mountain, dark, micaceous gneisses were noted in conspicuous ledges. Along the road from the East Hook to Hortontown, these were succeeded near the summit of the mountain by a light granite interbedded with the gneisses and estimated to be from forty to sixty feet thick. I have called this the Shenandoah mountain granite. With the exception of one or two quartzitic members, the usual succession of the gneisses is crossed in going from the granite “stratum” across the mountain to Hortontown. On the whole, the micaceous types seemed more abundant. Outcrops are numerous along the road and in the fields on each side. The age of the granite can not be affirmed. It appears to have the strike of the adjacent gneisses; but it did not prove possible to trace it more than a few hundred feet. The quartzite formation, or its possible equivalent, was not found resting on the granite, so that its age could not be definitely assigned by showing an unconformity. If thrust up into the gneisses at the time of their folding, it has escaped foliation. It probably belongs to the Precambric series. If so, the absence of foliation indicates that Postcambric movements did not contribute to the characteristic foliation of the gneisses. The eastern gneiss mass. The rocks along the northwestern base of the eastern gneiss mass in some cases suggest a continuation of those of Shenandoah mountain. 1The spur next east is locally known as Shenandoah mountain, from the hamlet of that name at its northern termination. The Shenandoah of the map is East Fishkill Hook. WTSIP YOOH TATYSH] Io 94} UL YWUUS OzUO;Y JO WAR}; dy} UO UDdyR} ydersojoyg ‘opsue MOT B J JSVOYFIOU OY} OF SdIp punoIsstO}F 9Y} UL dpIzJIeNb sy} oTYM ‘o[sue Yysty e& je ysvayynos Aq ysvo ay} 0} sdip [jem oy} puosoq sstous poyeprys oy yp, ‘oyzjsenb daquivg JOMOT OY} PUL SSIOUS ITIqUIBIAIG 94} UdaMjoq AjIUWIIOJUOUN 94} SUIMOYS > al + - 4 . : \ bem = H < , ‘ - - 1 ~ > 4 a ~ u i . . { A a f GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 25 At Fowler’s kaolin mine, east of Shenandoah, a rock was found beneath the kaolin deposits that was almost identical with the Shen- andoah mountain granite, though coarser in texture. The decom- posed rock, from which the kaolin was derived, is usually coarse, showing quartz chunks the size of a walnut in a mass of altered feldspar. Probably the kaolin is the product of the disintegration of a pegmatitic granite. The clay beds are apparently not very extensive, although their exact extent is obscured by glacial deposits along the slope. If the kaolin is thought of as the decomposition product of an arkosic, conglomeratic quartzite, it is difficult to account for the granitoid texture of certain specimens examined and the perfect resemblance which they have to the Shenandoah mountain granite. The quartz chunks are not rounded as one would expect in a conglomerate. A careful search failed to reveal the quartzite in the neighborhood. The structural features suggest that certain gneisses of this mass probably are faulted portions of the Shenandoah spur. Their resemblance might, of course, be explained as due to repetition. At Hortontown, near the quadrangle boundary, there were noted certain gneisses which had an almost unmistakable sedimentary ap- pearance. Though firmly crystalline, the quartzes frequently show a granular character on the fresh surface of the hand specimen, and the thin interlocking and dovetailing light and dark bands and fine texture indicate an impure sediment. ‘There is nothing about such varieties that points to an altered igneous rock. The gneisses of the eastern mass were examined in their outcrops along the base of the northwestern slope, along the mountain roads and to some extent along the wooded summit. It did not prove possible to assemble them into an orderly series. They present irregular repetitions of hornblendic and micaceous gneisses with some few minor variations. The micaceous gneisses were the more abundant. No decidedly massive types were noted. The thin sections are not conclusive as to the early condition of these gneisses, although in many cases they hint at altered sediments or ancient derivatives. PEE RGINETS Sm NETERS The Glenham belt. The southern extremity of this belt is a few yards northwest of the dam at Groveville. Above the dam it forms the west wall of the gorge of Fishkill creek as far as Glenham. Northeastward it may be followed distinctly as a narrow belt as 26 NEW YORK STATE MUSEUM far as Vly mountain. North of this hill it disappears against the slates. The belt is bounded by the slates on the west throughout its entire length. Vly mountain is cut off from the main mass by a transverse fault which has offset the main belt to the west by its own breadth. This fault is occupied by a large swamp, to which the eminence probably owes its name. The mountain is bounded on the east by the slates and on the south by the Fishkill limestones. The latter border the main portion of the belt on the east to its southern extremity. ‘The southern end of the strip is faulted against the slates. Mather called this mass a ‘ ‘ granite rock ” in his description! and in his section the “ Matteawan granite” (see plate 12, loc. cit.). He separated it from the gneiss of Bald hill, but apparently regarded it as a part of the Highlands. IX. IXmmons? cited this rock as an example of the uplift of in- ferior rocks into the newer ones. He described the relations at Glen- ham. His section is given herewith. : Fig. 10 a, slate; b, granite (of Glenham belt); c, limestone; e, Fishkill mountain. (After Emmons) Hall and Logan, in 1864, called it an ‘altered sandstone,” * J. D. Dana, in 1870,* referréd to it as “ bastard granite’ and described it as one of the “stratified deposits as is shown by its conformable position and by its taking the color of the slate near its junction.” The Highlands were the source. Smock in 1886° expressed doubts of its being stratified. He placed it with the Highlands, though the prevailing types of rock were unlike the characteristic varieties of the Fishkill mountains. In the southern portion of the Glenham belt the prevailing rock is a massive variety of the granitic gneiss. This is exposed for some depth in the railroad cut west of Glenham station. It is of dark green color and shows scarcely any tendency to foliation. South of this cut and for some distance to the north. surface out- crops are almost always of this type of rock, though varying in 1 Geology of the First District, 1843, p. 437. 2 Agriculture of New York, Part IV, 1846, p. 103. | Amer, JOUt. Sck, sen 2, 40:07 “Amer, Jour. Sct." Ser. 3, 27 480. ° Thirty-ninth Ann. Rep’t N. Y. State Museum, p. 176. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE PAGE the degree of chloritization of the mica. It is without evidence of bedding. This rock grades in places at the south into a laminated finer-grained variety which is common in the gorge of the creek below the railroad bridge at Glenham. At the north this type is more abundant, outcropping frequently between the road from [ish- kill Village to Wappinger Falls and Vly mountain. Vly mountain is composed of this variety. It grades into the coarser rock and, like the latter, is usually chloritized, though the red color of the iron usually predominates. The laminations strike between n. 12° e. and n. 15° e. As was noted in the petrographic description of this gneiss, it occasionally passes into a rock com- posed only of feldspar and quartz. The varieties so far described make up the surface rock of the Glenham belt and are the ones which have been emphasized by most observers. The road from Fishkill Village to Wappinger Falls crosses the Glenham belt diagonally about midway of its length. Several shal- low cuts have been made in the gneisses along the road. Beginning at the first cut on the south, the section is through about one hun- dred feet of a coarse, granitic hybrid rock. This is followed by hornblende gneiss and at the top of the hill the latter is succeeded by a banded, slightly crinkled gneiss with pinkish red and dark green laminae. A hundred yards beyond to the north of this rock on the west side of the road is a massive, coarse granitoid gneiss with quartz, light colored feldspar and biotite as the chief minerals. The joints in this rock are filled or faced with epidote. Beyond this is a fine-grained pinkish rock carrying epidote in many places and very similar in essential mineralogy to that described in the Mount Beacon brook section as composing the wall of the gorge above the bridge. Beyond this the cut is for some distance through medium- grained hornblende gneiss exposed on both sides of the road. The last section, on the east side of the road, is mainly through this hornblende rock which shows slight variations and fairly distinct “bedding,” with a southeast dip. These gneisses of the Glenham belt show no distinct types, except as described above for the surface exposures. On the other hand, the hornblende and other gneisses show marked resemblance to the mountain rocks. Roughly correcting the section for the gradient, the bearing of the road and the angle of dip, which seems a little smaller than that of the mountain gneisses, the thickness of the gneissoid types is similar to those observed in the gneisses of the spurs. to CA NEW YORK STATE MUSEUM The Matteawan inliers. The coarse granitic rock so character- istic of the southern portion of the Glenham belt forms a small inier farther south in Matteawan. It begins in “ Rock Hollow,” just west of the intersection of Washington avenue and the road that connects the latter with Liberty street, and extends south across Rock Hollow road (Walnut street) to Anderson street, and then aS a narrower strip to Grove street. (See map of Matteawan, fig. 8.) The rock here is not quite so deeply chloritized as in the Glenham belt. Another mass of similar rock, about 700 feet long by 400 feet wide, les to the south of this and forms the conspicuous knoll on which the Matteawan schoolhouse stands. The principal outcrops are between Spring, East and Falconer streets. This mass almost certainly connects with the gneisses in the eastern part of the town, but outcrops are concealed along Mill, Louisa and Washington streets and Mountain avenue between this mass and the westernmost out- crop of the gneisses at the east. Limestone may overlie the gneiss in this interval. The latter outcrops between Woodall and Henderson streets, and presumably has or had an eastward extension from here. The first inlier described above is succeeded at the south by the basal quartzite which forms a knoll between Anderson, Walnut and Grove streets, and is separated from the Precambric on the north and west by Anderson street. The contact could not be found; it may be faulted. The quartzite is overlain by the limestone on the east and south and on the west for a distance of 75 feet north of Grove street. A small mass of slate has been faulted in between the lime- stone and the spur of the Precambric on the west of Anderson street, near the house of Mrs C. E. Phillips. At the northern end of the Glenham belt on the southwest side of Vly mountain, north of the road at its base, a small knoll of quartzite, overlain by limestone, has been faulted with the gneiss of the moun- tain. It is separated from the main mass of foliated, reddish gran- itic gneiss by a narrow gully. As noted above, a coarse granitic rock of a mineralogy quite similar to that of the coarse granitic variety of the Glenham belt and the inliers at the south, occurs in places in the bed of Mount Beacon brook above the bridge. It occurs in outcrops among the gneisses in the eastern part of the town and was noted on Prospect street, 50 feet north of its junction with Walcott avenue and at the corner of Vail avenue and Washington street. The mineral epidote is of frequent occurrence in the Glenham belt and in places among the gneisses in the eastern part of the town of GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 29 Matteawan, and the rock which carries it in these different localities is often of very similar mineralogy and appearance in other HESPECLS. Interpretation. The Matteawan inliers connect the Glenham belt with the Highlands in a very satisfactory way. Other field relations which are cited above, show that the rocks composing these inliers are of Precambric age. The banded gneisses seen in the section on the Wappinger Falls road across the Glenham belt, bear strong resemblance to many of the gneisses outcropping in the town of Matteawan along the base of the mountain. The hornblende gneiss in places is identical with those occurring on the road from Brincker- hoff to Johnsville across the Honness spur. When the dip may be observed in the gneisses along the Wappinger Falls road, it is prac- tically the same as that of the Highlands rocks. The essential identity as to the age and fundamental likeness in mineralogy and relations of these inliers with the Highlands is almost certain. The character shown by the rocks which make up so much of these inlying masses, and upon which most observers have dwelt, apparently admits of ready interpretation. During the time the early Paleozoic sediments of this region were being laid down the sea was progressively transgressing upon and overlapping the old land mass from which its sediments were de- rived. This old land mass would doubtless have become decayed for moderate depths beneath the surface, or at least would have suffered some changes in the minerals composing the rock. Where subaerial disintegration actually took place, its products may. have remained undisturbed in favorable places, and it is possible to imagine that they were finally covered by the advancing waters without having been much sorted. In other cases they would have been washed away, leaving only the firmer rock, which probably, however, had undergone some mineralogical changes, such as the alteration of its ferromagnesian mineral. In other instances the disintegrated rock would have undergone partial sorting. In other cases it would have been completely sorted and a pure sandstone formed. In some places the advance of the sea would have been rapid enough to leave most of the material unsorted and only a superficial layer of partially sorted stuff. All would probably have been covered finally by a thoroughly worked over quartzitic sand that deepened offshore as the sea advanced. In the process of time burial in itself would have brought some changes in the subjacent altered gneisses; but the principal ones would have been effected by the same processes that changed the 30 NEW YORK STATE MUSEUM basal sandstone to a quartzite and metamorphosed the overlying limestone and slate. The partly disintegrated upper portions of the gneisses would have been thoroughly indurated into a compact rock and probably partially recrystallized. ‘The less altered gneiss would also have been changed, although not necessarily in such a way as to form entirely new minerals. Chlorite would now appear in a firm rock as a pseudomorph after biotite, or hornblende, and the old iron oxids would have been preserved as magnetite or hema- tite. In places where alteration had not taken place, the practically unchanged gneiss would be preserved. It is possible in this manner to account for the peculiar rock types of the Glenham belt and for the occurrence of such features as a coarse granitic “stratum” resting on upturned gneisses and _ fol- lowed by a somewhat foliated, finer-grained, quartzitic rock as shown in the gorge of Mount Beacon brook; or for the occurrence of such extensive surface developments of rock as the chief varieties of the Glenham belt, which so certainly rest upon and grade into the in- clined gneisses. Conditions would have been very favorable for the interaction of feldspars and ferromagnesians, which now find ex- pression in the abundant and widely distributed epidote that clearly belongs to an ancient period of alteration. A relatively large proportion of the ancient altered gneisses has been preserved in the Glenham belt. The section along the Wap- pinger Falls road, with its assemblage of altered and unaltered types, seems intelligible from this explanation. At places, as at Vly mountain, and near “ Rock Hollow ” in Mat- teawan, fragments of the quartzite have been preserved and these apparently grade into the underlying rock with which they are both unconformable and coextensive. These principles of subaerial decay have been applied in the foregoing discussion to certain altered gneisses and hybrid rocks occurring in many places among the Fishkill mountains. They serve to account for an evident ancient alteration in these recks and for the occurrence of certain types that are intermediate in character between the quartzite and the underlying gneiss. SUMMARY OF THE MICROSCOPIC CHARACTERS OF THE GNEISSES A microscopic examination has been made of about twenty-five sections of the gneisses of the Fishkill mountains, selected from types which were believed to show the principal variations in the gneissic series from west to east. A half dozen were also selected from the Glenham belt. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 31 These sections, except perhaps, those of the Bald hill granite gneiss and the Shenandoah mountain granite, do not afford any convincing evidence of the original character of the gneisses. ‘They give some support to the inference made as to their alteration and afford some ideas of the age of different characters in the rocks. In instances, they bear out the character as seen in the hand speci- ~ men and in the outcrop. In other cases, on account of the coarse- ness of the rock, they entirely fail to show the megascopic structural features. There are no striking variations: in the kinds of “ primary ” min- erals present, except in the ferromagnesian, although the propor- tions vary. Quartz is usually present, frequently in large anhed- rons only, but oftener both as large and smaller ones. Sometimes it is absent from the section or quite insignificant. Plagioclase 1s universal, often with orthoclase, but occasionally alone in types with much ferromagnesian content and little or no quartz. Ortho- clase is occasionally in apparent excess of plagioclase and micro- cline is frequent. Biotite often appears alone as a primary constitu- ent, being clearly of the same age as the other essential minerals. Hornblende often occurs alone in the same relationships. Buiotite sometimes occurs with hornblende, but then often suggests a sec- ondary character from its distribution and subordinate amount. Magnetite is abundant and is evidently secondary. It occurs chiefly in irregular grains in bunches or as dust masses in or near the ferromagnesians, or scattered about the section within the feldspars and along fractures. It is occasionally pseudomorphic after the ferromagnesian. ‘The latter are plainly very ferruginous in char- acter. Zircons are numerous and widely distributed. Tuitanite ap- parently occurs as leucoxene about the magnetite at times. Chlorite is abundant, often replacing all or most of the ferromagnesians in the section, but this mineral is associated with the gneisses which, in the hand specimen, betray an ancient alteration. Muscovite or sericite occur only as secondary minerals in the feldspar, except possibly in the Shenandoah mountain granite. The textural features present some variations, but they do not as a rule help much in deciding the question of whether the rock is sedimentary or igneous in origin. Very often the arrangement is very similar to that in plutonic rocks of the granitic or dioritic types and the modifications shown might readily be explained as due to conditions imposed on a magma. Other gneisses, either from a more granular character or from the abundance of the ferro- magnesian mineral, suggest altered sedimentary types. But these 32 NEW YORK STATE MUSEUM features are plainly far from decisive. On the whole, the sections are less satisfactory than the field outcrops; but so far as they go they sustain the uncertainty of the field examination. If these gneisses are mainly altered sediments they have been so thoroughly crystallized that they now often closely resemble igneous types. The hornblendes in their relation to the feldspars sometimes indicate a formation in the usual order of crystallization from a magma. If mainly of igneous origin, these gneisses were greatly squeezed in their formation and would now be more properly desig- nated gneissoid eruptives than eruptive gneisses. In either case the primary minerals (that is, those plainly belonging to the last change that affected the whole rock) and their essential arrangement are of contemporaneous origin. . So far as examined, the sections are entirely free of the minerals usually found in areas of profound dynamic metamorphism. It is, of course, impossible to tell how many complete metasomatic or other changes these rocks may have undergone, but there appear to be no traces of any antecedent generations of minerals. The sections sustain the belief that the primary features of the gneisses, as a whole, are of very ancient character and of Precam- bric age. They show, on the other hand, many evidences of subse- quent metamorphism. This later metamorphism is shown in the sections in several ways, but chiefly as pressure effects. In almost all cases the quartz crystals show pronounced strain phenomena, such as strain shadows and Wavy extinction, and are often cracked. The plagioclases almost always show pinched-out, bent or broken lamellae. Fractures and long cracks are common. In places where the gneiss evidently had undergone an early alteration, the rock was indurated and occasion- ally new minerals formed. Some molecular movement is indicated by chloritic fillings, disseminated magnetite and secondary quartz injected into the feldspars. Some biotite very clearly belongs to this later metamorphism. Some of the sections from the Bald hill gneiss and those in the bed of Mount Beacon brook show fewer appazent strain effects than those from the spurs farther east, which may be interpreted as the expression within these rocks of a somewhat lesser degree of metamorphism at the west. The conclusion that the primary gneissic characters were changed very little in Postcambric time seems inevitable. As the field relations show the gneisses had reached practically their present crystalline condition and gneissic structure GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 33 in Precambric time. Because of their early crystalline condition, these gneisses would have undergone fewer changes and a relatively lesser degree of metamorphism than the sediments which overlay them, during the mountain building process of Ordovicic time. Such changes as they underwent from this cause should, however, show some correspondence with those in the younger rocks, as is perhaps afforded in the apparent lesser degree of metamorphism at the west. This difference is not, however, noticeable in the field unless the more clearly “ bedded” strata in the bed of Mount Beacon brook and the more clearly definable nature of the altered Precambric gneisses of the Glenham belt are indications of it. An examination of the thin sections of the gneissoid types from the Glenham belt entirely supports the assertion that these rocks are members of the Highlands gneiss series. In mineralogy, texture and metamorphic characters they are entirely similar. The thin sections of the more characteristic types of this belt afford the clue to their interpretation and seem to show their original nature. They also carry characteristic strain effects. BAWIERS IN -DEs GNETSSES During the Green mountain uplift the Precambric gneisses appar- ently buckled somewhat, but seem to have yielded chiefly by break- ing. These faults greatly complicate the problem of the configura- tion of the Precambric land mass while the quartzite was being laid down. Beginning at the west, the first fault is that shown by the Glenham belt. A reversed or thrust fault has thrown the gneisses against the slates on the west and south. Evidently the slates were folded and overturned and then overridden by the older rocks. The strati- graphic displacement necessary to elevate the Precambric into con- tact with the slates must have been an extensive one. Apparently at Vly mountain the upthrust was greater, resulting in the elevation of the mountain mass above the main portion of the belt and caus- ing the transverse break between the two. ‘That Vly mountain is not mainly an erosional feature is indicated by its relationships. It forms an isolated block which is faulted against the slates on the west, north and east. The transverse fault on the south involved the limestones which were bought against the slates on the east of them. The gneiss and limestone form the upthrow as a result of reversed faulting, both resting against the slate. The gneiss apparently also moved with reference to the limestone. Pro- 34 NEW YORK STATE MUSEUM jected southward, the fault on the east of Vly mountain falls in line with the scarp on the east of Bald hill (see plate 5). The gneiss inliers in Matteawan, south of the Glenham belt, are also clearly faulted against the slates on the west. A long swamp borders the northern one of these on the west, while on the north it is in faulted contact with the slates. The relationship existing between the limestone and the gneiss all along the eastern margin of the Glenham belt and the smaller masses at the south, is far from plain. Although relatively small, there is probably some stratigraphic displacement, in places at least. The Bald hill mass shows a still greater vertical displacement. As now uncovered, the break is partly within the gneiss itself and partly along a contact with the limestone, and probably in some places with the quartzite. The slope of the gneiss is always very steep and often precipitous. A moderate slope at the base, in places, may be interpreted as that of the quartzite or the surface from which it has been removed in late geological time. This kind of slope usually changes abruptly to a sharp angle with the vertical in ascending the mountain. The abundant talus at the bases of these scarps is misleading and gives the appearance of a much gentler slope than they really possess. The complementary result of recession of the summits by weathering is also confusing. Apparently the overthrust which elevated the Bald hill mass involved a larger area of the gneiss. It seems reasonable to explain the faulted contact of the gneiss of the Mount Honness spur and the Fishkill limestone on the northwest of it as primarily due to this thrust. Later or simultaneous tension faulting dropped the limestone east of Bald hill into its present position. A number of scarp faces at different elevations along the northwestern slope of the Honness spur in line with the strike of the gneisses, and visible even in the season of foliage, mark tension strike faulting of dimin- ishing intensity eastward from the great normal fault on the east of Bald hill. The eastern face of Honness is marked by a rather conspicuous normal fault scarp which diminishes and dies away to the south- ward (see plate 6). The throw here was not so great as on the east of Bald hill. Along the west side of the east road from West Fishkill Hook into the mountains, is a drop fault of small displacement. It is marked first by a cliff of the quartzite, but higher up the mountain it is in the gneisses. | ITY preg Jo ysvo oy} uo divos yNvy oa G 93e1q GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 35 On the east of the Hook spur another fault of moderate dis- placement has dropped the quartzite and limestone into the East Hook. The northwestern slope of Shenandoah mountain is very steep from the point where it cuts the southern boundary of the quad- rangle nearly to Shenandoah. The quartzite has a northwest dip of approximately 50°. The gneiss in places shows precipitous ledges, though these are not very high. The angle of slope changes abruptly from quartzite to gneiss. The steep dip of the quartzite shows considerable disturbance before the break occurred. East of Shenandoah mountain is a clearly defined normal fault scarp along which the younger rocks were dropped. Their erosion has formed Shenandoah hollow. Along the northwestern slope of the eastern gneiss mass are very steep and precipitous scarps, sharper even than those of Bald hill. The drift-covered talus slopes at their bases are not to be confused with the quartzite. It is probable, however, that in places the quartzite was involved in the upthrow and was brought against the limestone. These breaks are interpreted as the result, primarily, of the com- pression producing the Green mountain elevation. The tendency was to produce a system of flexures like those in the younger rocks at the north. The gneisses buckled relatively little but, unable to resist the great pressure, were broken and thrust up into the younger rocks. Tension faulting within the expanded arc accompanied or followed the upward thrusting. The faulting in the gneisses is clearly subsequent to the de- position of the quartzite. The only disturbance capable of produc- ing these effects would appear to have belonged to the close of Ordovicic time. These faults would certainly have greatly disturbed any orderly sequence which the gneisses may have had. SUMMARY AND CONCLUSIONS The relatively brief treatment of the gneisses of this quadrangle given above results from the impossibility of assembling them into an orderly sequence. ‘The thickly-wooded character of the country, the presence of faults and the difficulties introduced by ancient subaerial alteration, greatly hinder their study and make a Satisfactory map practically impossible. 9) oa 36 NEW YORK STATE MUSEUM The origin of the gneisses is very obscure. In some respects they appear to be largely igneous in character. In many places their sedimentary origin seems almost certain. It is entirely possible that the two kinds occur together in a parallel and roughly alternate arrangement, but faulting makes it impossible to decide this point in the face of the other difficulties present. The thickness is too great to permit the interpretation of a monoclinal series. It seems entirely justifiable to attribute the apparent igneous character to profound metamorphism. It is plain that if the eneisses represent a sedimentary series in any part, the strata must © have been jammed into close folds and overturned. If folding was accompanied by the injection of igneous rocks along the axes of the anticlines, the accompanying alteration would have been very severe and both sedimentary and igneous types would have come strongly to resemble each other. There would probably be no dis- tinguishable exomorphic and endomorphic effects to aid in separat- ing the two. The gneisses below the bridge in the Mount Beacon brook section show a “ bedded ”’ character more clearly than at any other place. The general absence of crumpling and crinkling in the gneisses is noteworthy in considering the possibility of their sedimentary origin. Interbedded limestones, if such could be found, were thought of as likely to afford the most convincing evidence of a sedimentary series in these gneisses. Dr C. P. Berkey has discovered such lime- stones in the Highlands farther south’ and in the Fordham gneiss of New York city. The possibility that the basic rock and bastite ledges at Hortontown, described in the following pages, might be altered calcareous and magnesian sediments of Precambric age was considered, but the field relations do not easily permit this interpretation. Taken as a whole, the gneisses in this quadrangle present sufficient diversity to be considered, at least in part, as an altered sedimen- tary series. NAME AND CORRELATION Dr C. P. Berkey* has correlated the basal member of the Man- hattan series with the basal gneisses of the Highlands and has 1Structural and Stratigraphic Features of the Basal Gneisses of the Highlands. N. Y. State Mus. Bul. 107, 1907. 2 Science. n. S., 37 :936. ® Structural and Stratigraphic Features of the Basal Gneisses of the Highlands. N. Y. State Mus. Bul. 107, 1907, p. 361. JLISIP YOO] ISIA\ OY} wody Ud9S SB ‘ssoUUOFY JUNOP FO 4svo oy} UO d4vds qpNey | 9 21d | GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE Sy, called the whole the Fordham gneiss. This he correlates with the Grenville of Canada and the Adirondacks. ei ORTON TOWN BASI©C PRUEPLIVE AND AS SOCEM DD Vii AMOR E ENC ROCKS General relations. In the orchard by the house and near the _ barn on the farm of Albert Lawrence at Hortontown, are several outcrops of a massive, compact, greenish rock. One or two ledges are of moderate size, but most of the outcrops are small and incon- spicuous. This rock is traceable only a short way to the north or south by actual outcrops, but in the fields and stone walls south of the orchard there are numerous boulders of this rock. The actual ledges disappear beneath the hill to the southwest of the orchard. At the summit of this hill, in a west by southwest direction from the house, and about 200 or 300 yards away, are numerous ledges of a rusty, blackish rock, which may be followed to the southwest ton a short distance and then are lost. Just to the west of these outcrops, on both sides of the road and in the road itself, are numer- ous outcrops of quartzite with southeast dip and a strike east of north. A conspicuous ledge of this quartzite borders the west side Ouevereade.) West of this)is a cully about 50 of 75 feet in width which at the west is bounded by a perpendicular cliff of the eneisses. The relationships just described are indicated on the accompanying sketch map (see figure IT). It was not possible to determine the configuration of the mass to which the greenish rock belongs. The east-west. distance be- tween outcrops was estimated at 50 feet, but there is reason for thinking that the rock has a greater extent. Petrography and general description. ‘The greenish rock is very tough. It shows variations from a greenish black rock, streaked with lighter green, through a mottled variety to a lighter, greener rock with a tendency to fibrous structure. The rock may be cut with a knife. Some varieties, when pol- ished, give a rich, dark, glossy finish. When powdered and tested by the magnet-it reveals large quantities of magnetite to which the darker hues are due. Weathered surfaces show freckles of black and greenish yellow, caused by the bleaching of the microscopic crystals among the magnetite grains. The thin section in transmitted light shows innumerable dustings and irregular grains of magne- tite, while the rest of the section is yellowish white. With crossed 38 NEW YORK STATE MUSEUM nicols the latter appears as a network of spindles, flakes and needles of bastite. There seems to be no trace of an antecedent mineral (see figure I2). The ledges of the black rock are prevail- ingly rusty. Excavation has been made at one place to a depth of two or three feet, apparently in a search for ore. | These ledges are in- conspicuous, and, when surrounded and _ over- grown by grass, are readily missed, except in systematic search. The hand specimen shows avery coarse tex- ture. The rock is made Fig. 12 Bastite rock at Hortontown. Actualsize 3 mm. , é Showing a network of bastite needles and spindles with up chiefly of massive ip euipee. tet hornbiende. There are patches of finer texture in which magnetite is abundant. Small pyrite grains are frequent. In some places the hand specimen shows a relatively porous mass of rounded grains as though some mineral had been dissolved away. The rock has a high specific gravity and in almost all cases is rusty in color. The thin section shows large, irregular pleochroic brown and green hornblendes, with some pyroxene. Magnetite inclusions are numerous and this min- eral also occurs abundantly along numerous cracks, sometimes in association with serpentine borders or fillings. The ledges of the quartzite are more numerous and more ex- tensive than those of either of the other rocks. Its apparent width is about 75 or 100 feet. It is thin-bedded and steeply inclined. It is very similar to the basal quartzite as seen at certain places and appears to belong to that formation. It may be followed distinctly for several hundred feet. At the north and south these types give way to the characteristic eneisses of the mountains. The exact field relations of these rocks are very obscure. No contacts could be found. Seemingly the only clue to their age and relationships is to be obtained from the structural features and the associations. CO E RUPTIVE AINEISS Fig. 11 Sketch map to show the general relationships at Hortontown. Scale approximately 200 feet to the inch. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 39 Interpretation. The possibility suggested itself that some of these rocks might be members of the basal gneiss series. The quartzite, however, is almost certainly Paleozoic in age. he black hornblende rock has the characters of a basic eruptive. The green serpentine variety gives little idea of its original character, but it 1s apparently not an altered pyroxenic rock. The southwestward continuation of the reversed fault along the northwestern slope of the eastern gneiss mass would apparently intersect the fault on the east of Shenandoah mountain in this neighborhood. The latter scarp is only a short distance west of the quartzite. This intersection would have been a most favorable point for an igneous intrusion. Some of the basal Paleozoics were evi- dently caught at this intersection and intruded by the hornblende rock. The quartzite offered little for the eruptive to act upon. The bastite rock very probably represents an impure ferruginous dolo- mite. From what is known of bastite, it is commonly, at least, the alteration product of orthorhombic pyroxene; but the present rock gives no indication of the former presence of any antecedent min- eral. There seems to be no grave objection to the inference that the passage was direct.’ This is the only occurrence within the quadrangle that permits the interpretation that an eruptive has penetrated and altered the overlying Paleozoics. (iio pS OUT ZItE (ROUGE OUAG) Distribution and general structural features. This formation, which has frequently been mentioned in connection with the gneisses, in this quadrangle occurs only in proximity to the Pre- cambric rocks. , In the town of Matteawan the quartzite forms a small inlier as described above, in connection with the first small inlier of gneiss south of the Glenham belt (see page 28). Outcrops were also seen just north of Howland avenue in the open field at the foot of the Mount Beacon incline. The only other outcrops which have been noted in this vicinity occur farther north along the base of Bald hill on the Maddock estate.2 About 300 yards south of the house and well up in the woods, about 200 or 300 feet east of the private 1 Professor B. K. Emerson assisted the writer in the identification of the mineral bastite. 2 The presence of the quartzite at this point was discovered by a com- panion, Mr W. R. Clarke. 40 NEW YORK STATE MUSEUM drive, are two or three good-sized ledges. Farther up the hill on Mountain street at the point where it forks, going east, is an outcrop of the quartzite. This was first interpreted as a boulder, but the proximity of this rock in place farther down the hill suggests that. it is a small ledge which has been preserved. These outcrops are the only ones which were noted in this town, after a careful search, which were referable to the quartzite as typically developed in this quadrangle. As has been discussed above, there is strong reason for thinking that certain phases of the gneiss owe their peculiar character to the subaerial decay and partial sorting which took place during the epoch of the transgression of the sea in which the quartzite was laid down, and are therefore of the same general age. At Vly mountain a small patch of the quartzite has been pre- served just north of the road on the south side of the mountain at the summit of the hill as the road descends into the swamp, going west. A careful search was made along the northwestern base of Bald hill from the Maddock farm to the northeastern end of the spur. The topography between the more precipitous portion of the hill and Fishkill creek often suggests the presence of the quartzite. Out- crops are few and the gentler basal portions of the slope are usually drift-covered. ‘The foliated Bald hill gneiss outcrops in places north of the Maddock residence between it and the farmhouse at the north- east. QOutcrops are absent at the base of the gneiss to the northeast of this farm, nearly to the end of the spur. The ledges of gneiss often rise precipitously from the edge of the gentler portion of the slope and the bases of the scarps are hidden by abundant talus which, in many cases, doubtless forms the gentler slopes. Near the extremity of the spur, due south from Fishkill Village, a ledge of the quartzite was discovered in the woods near the edge of the gneiss. The gneiss extends to the north of this ledge. The Bald hill thrust carried the quartzite with it in places before the rupture occurred and in these places a characteristic quartzite slope has been preserved. Only a few scattered ledges now mark the former presence of this formation in the eastern part of the town of Matteawan. The small ledge near the extremity of the spur seemingly belongs with the upthrow block and probably rests by thrust against the limestone. It is a question whether the precipitous ledges of the gneiss northeast of the Maddock farmhouse rest against the quartzite or the limestone. | GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 4i The map represents the quartzite slope, with the break to the southeast of it passing into the limestone southwest of the Maddock farmhouse. Northeast of that point it shows the gneiss against the limestone for a distance as indicating the tendency of the thrust, and then against the quartzite, with a probable break between the quartzite and the limestone. There are no traces of the quartzite south of Fishkill Village in the valley of Clove creek, nor along the northwestern base of the Honness spur. Along the northwestern base of Mount Honness _ proper the gneiss is only 50 or 100 feet from the limestone, from which it rises in bold ledges. The quartzite may once have covered a portion of the northwestern slope of this spur. East of Honness, about one-third of a mile south of Johnsville, the compact quartzite with some conglomerate outcrops for a short distance in the woods at the base of the scarp, but is soon lost beneath the kames which rest against the cliff. South of these kames on the farm of Irving Knapp, as mentioned above, a large mass of rock with northerly dip forms conspicuous ledges in the east fork of the mountain roads. It resembles both the quartzite and the gneiss and probably represents a transition from one to the other. The quartzite outcrops along the road east of Knapp’s, in one or two places, but is mostly concealed by drift west of the west road from the Hook into the mountains. It was found in the bed of the brook just west of John Ireland’s house and about 300 yards south of the Thomas Carey farm on the roadside just above the brook. Some conglomerate occurs at this point. Eastward from the Carey farm, on the farms of Garrett Smith and Ward Ladue, it forms large conspicuous ledges and extends to a point one-fourth of a mile south of Garrett Smith’s and terminates with an abrupt talus slope in the woods. ‘The unconformity between the quartzite and gneiss is plainly shown just south of Alonzo Smith’s (see plate 4). East of the east road into the mountains, the quartzite extends a little farther south before the gneisses are reached. The southern boundary swings round northwest of the McCarthy place and then east through the woods across the Hook spur to the fault on the east of this. At this point the quartzite was dropped by a fault and is now concealed by surface deposits nearly to the quadrangle boundary. Just north of the road on the west side of the brook it appears in large ledges. Low ledges of limestone outcrop in the meadow just east of the brook. Near the quadrangle boundary a small brook, which comes down from Shenandoah mountain, has cut through the surface deposits. 12 NEW YORK STATE MUSEUM The quartzite was found exposed well up the slope in the bed of this brook dipping 50° to the northwest with a strike of n. 49° e. following closely the strike of the ridge. For a mile and a half to the northeastward this formation forms a clear topographic feature, though concealed by drift. Farther on it outcrops frequently and in large ledges along the south side of the road from the East Hook to Shenandoah. It crosses the road less than one-fourth of a mile west of that hamlet and is succeeded by the gneisses. There are numerous outcrops of the quartzite just north of Shenandoah. It is probably cut off at the east by the fault that borders the mountain on the east. The quartzite is absent along the eastern base of Shenandoah mountain until one reaches the mass associated with the basic eruptive at Hortontown (see page 39). Along the northwestern slope of the eastern gneiss mass the topography from the schoolhouse near Hortontown to Fowler’s kaolin mine suggests the presence of this formation. The quartzite was not found and the lower portion of the slope is covered with drift which contains frequent large quartzite boulders. The kaolin rock at Fowler’s mine may represent the quartzite. It seems likely that the gneiss rests against the limestone southeast of Shenandoah, and that the quartzite has since been eroded. South of the junction of the Hortontown and Mountain roads, gneiss is the outcropping rock in the valley of the brook as far as Hortontown. Along the slope of the eastern mountain mass, northeast of the kaolin beds and the ore deposits, everything is beneath the drift for a long distance at the base of the mountain. The gentle slope which is present is probably due to talus. No outcrops of the quartzite were found. South and southeast of Charles E. Bailey’s the lime- stone is only a short distance from the precipitous gneiss. Just north of the road at the base of the mountain scarp, east of Bailey’s, a wide swamp extends northeastward. Three-fourths of a mile east of the point where this road turns southward into the mountains the quartzite was found in good-sized ledges within the edge of the woods. The conditions along this slope resemble those described for Bald hill. There was a tendency for the quartzite to fold somewhat before the rupture occurred, and the slope of the hill marks the slope of the quartzite as seen southeast of Shenandoah. Toward the northeast the rupture occurred earlier, so that the gneiss now stands in precipitous ledges against the limestone. Farther on, east GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 43 of Bailey’s, the quartzite was brought against the limestone marking a diminishing tendency in the thrust to the east. As shown on the map portions of the quartzite are yet preserved near the quadrangle boundary. Where the quartzite could not be found the gneiss is represented as resting against the limestone; but in some cases, as discussed above, the quartzite may have once been present. The wide swamp east of Bailey’s marks the northeastward con- tinuation of the great thrust fault along the limestone-quartzite contact. Petrography and general description. This formation has great uniformity of appearance and general character throughout tievanea, lits principal variations may be stated very briefly. Whe predominating variety is a compact, granular quartz-rock of medium grain. This grades into a fine conglomerate at the base in a few places and in others at the top into finer-grained quartzitic shales. The predominating variety is either white or pinkish in color. Feldspathic varieties are rare. Within the quadrangle there does not appear to be any apprecia- ble difference in metamorphism in this formation from west to east. At the type locality at Poughquag there is indication of a eneissoid character. Within this quadrangle the quartzite appar- ently never was involved violently enough to induce this structure. The thin-bedded varieties, often with shaly character, were noted at the northern end of the Hook spur south of the Hupfel estate, in the steep bed of the brook in the East Hook near the quadrangle boundary, north of Shenandoah and at Hortontown. Conglomeratic phases were seen southwest of Johnsville near Honness mountain, south of the Thomas Carey farm in the West Hook and north of the McCarthy place to the east of Ward Ladue’s. Strikes and dips in this formation vary greatly. In Matteawan good observations could not be made in the thick quartzite south of Anderson street nor at the foot of the Mount Beacon incline. Read- ings taken just south of the Maddock residence gave a strike of ise. ald cayvcipr ot 54" on. we Whe enetss, only, 20 feet away, dipped 50° to the southeast. Observations at the quartzite ledge at the extremity of the Bald hill spur gave a strike Of Mm 42 e€. and a dip of 48° to the northwest. A treading taken on the east of Honness gave a strike of m. 42° e. and a dip of 35° southeast. South of the Carey farm in the West Hook the dip is 15° to the northeast. On the farms of Garrett Smith and Ward Ladue, west of the fault, the dip is to the north- 44 NEW YORK STATE MUSEUM west. East of the fault it is to the northeast. As the boundary swings round the western slope of the Hook spur, the dip changes from northeast to north and northwest, and at the northern end of the spur from northwest to north. On Shenandoah mountain in the East Hook, near the quadrangle boundary, the strike is n. 49° e. and the dip 50° n. w. .This general strikeand@aip holds to Shenandoah. North of Shenandoah the dip changes to north. The quartzite disappears at the east under a mass of kames. Readings made a mile east of Bailey’s gave a strike of s. 70° e. and: a dip. of about. 18> n: e: : The quartzite thus follows the folds of the gneisses and, although eroded and disturbed by faulting, tends to fringe the spurs and hollows along the northern margin of the Highlands. The conformable series at West Fishkill Hook. East of the normal fault that extends along the east road into the mountains, the basal quartzite is overlain by bluish-gray limestones having the same dip as the quartzite. The nearest approach to actual con- tact is in Ward Ladue’s orchard, a few feet north of Jones’s barn. The pinkish ledges of granular quartz rock are only a few feet away from the limestone and the two are seen to be in strict con- formity. The limestone, which is greatly broken up into large blocks, can be followed to the south and east. In both directions it is suc- ceeded by the quartzite. The limestone swings round the north- western slope of the Hook spur and appears in numerous ledges in the fields southeast of W. L. Ladue’s barns. Here it is con- formably overlain by gray calcareous shales. At the eastern side of the pasture, south of the orchard on W. L. Ladue’s farm, the shales dip to the northwest and north. A little farther west, in the center of the field, the interbedded shales and shaly limestones have buckled into a low anticline. Fig. 13. Generalized section to show the conformable series of the Lower Cambric in the West Hook district. Distance approximately one-third of a mile Fossils from the quartzite and overlying limestone. With the exception of a few worm borings found in the quartzite along the west road from the West Hook into the mountains in the summer GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 45 of 1906 (see figure 14), fossils had not been discovered in this formation up to the summer of 1900. inmeaueust of that? year the writer discovered in the yard of Ward Ladue at the West Hook a fossiliferous slab Gi compact quartzite, about three feet square, and plainly derived from a bed about five inches thick. Both surfaces were covered with fossils, chiefly brachiopods and the cephalic borders and spines of trilobites. Some of the latter were from one and one- half to two inches long. itticeclanawas hom ad) Mile -Sralmeds m1, ) wer hornes an Lower gray quartzite bed and was very compact Ce eee and resistant. The fresh surface showed numerous rusty markings. This discovery led to persistent search for the fossiliferous rock in’ place. 3 Directly south from Ward Ladue’s house a gorge in the quartz- ite apparently marks the beginning of the normal fault displacement that extends southward just to the west of the public road. The western wall of this gerge is composed of thickly bedded compact quartzite. The eastern wall shows thinner rusty layers interbedded with the compact rock. The fact that only a hundred feet or so to the eastward the quartzite is overlain by the limestone, together with the evidence of faulting, were taken to indicate that the rocks in the eastern wall are younger than those on the western or upthrow side. With this assumption as a basis, and in the belief that the rusty layers interbedded in the superficial portion of the quartzite should yield fossils, if such were present, the eastern wall was given a very careful examination. No fossils could be found between Ladue’s and the point where the gorge intersects the road. Although the dip of the quartzite is very gentle along here, the thickness crossed is considerable. The gorge was then traced southward from the road. A rich assemblage of fossils was discovered in the eastern wall about 250 yards southeast of Herman Adam’s house. The ledge occurs just beneath an old stone wall that separates the gully from an old orchard. The fossil traces were first discovered in the compact rock similar to that seen in the slab in Ladue’s yard, and showing the same rusty markings on the fresh surface. This rock overlies 46 NEW YORK STATE MUSEUM some thinner, rusty, decomposed layers in which fragments of trilobites and brachiopods are very abundant. The trilobite fragments are smaller than those displayed on the slab described above, but in other respects are quite similar. They were identified as fragments of Olenellus, probably thompsoni. The brachiopods bear a strong resemblance to Obolella. Two speci- mens of the rusty quartzite crowded with fossils are shown in figure 15. Fig. 15 Fossiliferous Lower Cambric quartzite In the summer of 1908 the opercula of Hyolitheli@s micans were discovered in the limestone overlying the compact quartzite in Ladue’s orchard at an estimated distance of 20 feet above the latter. After a careful search another operculum was found at a slightly higher level in the first ledge east of the lower barn on Jones’s farm. Age and correlation. ‘These fossils prove the quartzite to be of Lower Cambric age. The similar relations which it has to the underlying gneiss indicate that it is the equivalent of the basal quartzite at Poughquag. The latter was described and named by Prof, J. D. Dana’ as the Poughquag quartzite. 1 Amer. Jour. Sci., Ser. 3, 1872, 3 :250—50. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 47 Summary and conclusions. The relationships among the quartzite, limestone and calcareous shale described above are ex- hibited nowhere else in this quadrangle. The field relations of the gneisses and the quartzite indicate that the older rocks have been thrust up into the younger series and that in general their present relative position must be regarded as very different from that which obtained when the Cambric sea over- lapped the older land. It is plain that the quartzite was involved in the thrust movement and, although never violently folded, was yet greatly disturbed by folding in certain places. In many instances the quartzite was moved bodily with the gneisses, so that where it is now present, or was apparently present up to a comparatively recent epoch, it is not contiguous with the limestones of its own epoch, but with later ones on which it has been thrust. A not unreasonable restoration of the Precambric floor, which is thus assumed to have been fractured and elevated, would allow a considerable extension of the thick quartzite formation south- ward from its present northern position. ‘The actual evidence for such a former extent consists in the faulted mass at Hortontown, which, since the thrust movement was northwestward, could hardly have had an original position farther northwest, but which might readily have come from the southeast, and in occasional ledges observed in the woods during a reconnoissance south from West Fishkill Hook across the quadrangle boundary. ‘The character of the slope of the quartzite where least disturbed, as in West Fishkill Hook, its thickness and the rather steep southern termination at certain places, indicate a former southward extension. The varying strike and dip of this formation is best interpreted as the result of disturbance subsequent to its deposition, rather than to original initial slope. In attempting to explain the present valley position of the younger rocks along the northern border of the Highlands, instead of assuming that they were deposited in valleys, we are offered the alternative explanation of down-faulting, and subsequent partial or entire erosion in which the ice sheet may have played an import- ant part. The Precambric masses may have stood as isiands in the early Paleozoic sea, but the present relationships do not require such an interpretation. The disturbance of the quartzite has given it such inclination that it might be regarded as of different geological age at different altitudes, Of this there is no evidence. 48 NEW YORK STATE MUSEUM THE WAPPINGER (BARNEGATE) LIMESTONE This formation appears within the quadrangle in two main belts with some smaller faulted masses lying between them. The west- ernmost main belt is the Barnegate limestone of Mather, but now commonly referred to as the Wappinger creek or New Hamburg belt. It is followed by Wappinger creek from the latter’s source near Pine Plains to the Hudson river, and its eastern contact with the overlying “ Hudson River” formation crosses the river at New Hamburg. The eastern belt is known as the Fishkill limestone, as it lies chiefly in the town of old Fishkill. THE WAPPINGER CREEK BELT This belt enters the quadrangle from the north at Pleasant Valley and continues in a southeast by south course to New Hamburg. It reappears west of the Hudson and continues in the same direc- tion beyond the western boundary. East of the Hudson it is broken up into a central strip, with a large rectangular strip on the west of this along its southern half and separated from it by a narrow band of the slates, and several smaller masses lying to the east of the central strip along its middle portion. THE WESTERN STRIP Boundaries. ‘This strip is clearly faulted against the slates at the north. The fault line runs in a southeast-northwest direction across the Poughkeepsie driving park. The western contact is marked at many places by swamps or scarps which indicate that the western margin is also a faulted one.” The presence of a fault along here receives confirmation from the apparent age of the lime- stone in contact with, or in proximity to, the slates. The western boundary begins just southeast of the junction of Hooker avenue and the road that runs southward from it on the west of the driving park and passes across the northwestern part of the Ruppert farm and just west of the old Hinckley house, and then may be traced by swampy ground or a low scarp to the schoolhouse at the corner of the Spackenkill and Poughkeepsie roads; thence under drift to the first road leading to the river. The limestone outcrops on the north side of this road in low-lying ledges and in more conspicuous ones south of it in proximity to the slates. From here the contact is 1 Geology of the First District, 1843, p. 410. . 2 This fault was described by Professor W. B. Dwight. See Amer. Jour. Sci Heb: 1236; 31:125-37, with) map: GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 49 indistinctly followed to the river, where the limestone terminates in a bluff. The northern portion of its eastern boundary is concealed by drift, but farther south to the east of the road that runs south- ward on the east.of the driving park the limestone forms a con- spicuous feature for several hundred yards along the eastern edge of R. J. Kimlin’s farm. Southwest from here it apparently follows Casper creek to the Hudson river. The slates which come in between it and the central strip form conspicuous ledges both north and south of the Spackenkill road and were noted southwest of the Poughkeepsie-Wappinger Falls road, on the east side of the road to New Hamburg, and also near the Hudson river. The lower reaches of Casper creek, west of the Poughkeepsie road, are choked with kame deposits. Terranes present. The Potsdam and Trenton horizons have been recognized in the strata composing this western strip of limestone. The Potsdam. Fossils belonging to this horizon have been discovered in a few places. The first were reported by Professor W. B. Dwight! from the northern portion of the strip. Just south of the Poughkeepsie driving park, and to the west of the new pri- vate road which runs south from the park to the Ruppert farm- house, are a number of low-lying ledges. They have yielded: BMtmathepiss pinmntorim Ss oo. minima, Ww. ac umit = tae Omotella “CGeingulelia) prima, .Obolella MecemMuline aia naqelatyceras «Ptychioparia (Con o- Sepuaiies) mn. sp: -Wicellocephalus, Ptychaspis, Stromato- cerium, encrinal columns.” A few months later Professor Dwight reported other Potsdam fossils from a locality about a mile southeast by south on the Spackenkill road, about one-half mile east of the Ruppert farmhouse, at the point where the private fod to the Warick farm leaves the main road. In addition to Eingulepis pinniformis and allied species found at the amet locality, he identified Ptychoparia saratogemnsis Walcott, and P. calcifera Walcott. These fossils may be seen in the museum of the Vassar Brothers’ Institute at Poughkeep- sie. Another ledge yielding L. pinnifcormis was found by Professor Dwight near the eastern margin of the belt about one-half mile southeast of the first locality described. This ledge is just east 1 Amer. Jour. Sci., Feb. 1886, 31:125-37. See also Trans. Vassar Bros. hist. 4.2ts0—7 12 2 rans, Vassar, Bros) Imst.,ve14, pt. 2) p) 200-14. s Amer. Jour. Sci. July; 1887, 34 :28-32. 50 NEW YORK STATE MUSEUM of the little house north of Mr R. J. Kimlin’s barn. The ledge carrying Solenopora compacta found by Professor Dwight is only a short distance to the southeast. In the summer of 1908 a new Potsdam locality was discovered by the writer. The beds yielding fossils were found in the quarry on the Ruppert farm about 200 yards north of the Spackenkill road. The rock was being removed for lime and blasting operations greatly facilitated the search for fossils. These are scattered and usually fragmentary. They are embedded in compact, resistant limestone which made the search difficult. A half dozen good specimens of © Lingulepis pinniformis were found, besides numerous fragments; also a head of Ptychoparia sp. A photograph of the quarry is shown in plate 7. Fossils seemed most abundant in the middle layers. Figure 16 shows two of the best preserved speci- mens of li -pitunifo rm es:. Fig. 16 Two specimens of Lingulepis pinniformis from the arenaceous Upper Cambric limestone beds at Ruppert’s quarry The rock in the floor of this quarry showed many peculiar mark- ings of concentric rings from three-fourths to one inch in diameter. These were sectioned and examined by Professor John M. Clarke. A part of a letter from Dr Clarke referring to these structures is given below. ‘“T have had the specimen you sent to me cut and polished in the hope of bringing out some structure from the concentric masses therein. The result is not very satisfactory, except as indicating what seems to be an inorganic origin, though I would not be willing to say that the masses were not spongoid like Streptochaetus. The successive laminae might indicate such a structure, but the intimate composition of the skeleton has been so altered by granulation as to seem to leave possibility of organic structure pretty hazy; yet I am inclined to believe that the rock carries organic remains, as ‘ds erszedoyoAj}q pue stwiofyruurd ey nsuryT Pepfatd savy ssakey] appiw sy som oy} 0} ApWYSr[s dip speq esoy fT, ‘osdsoyxysnog JO jsvoyjnos wey Sjioddny je Atienb 9y} ul Speq s1Iquiey Joddy [eJuOozIIOY Jsowye 94} Surmoys ~ - + = = - f ' -: ) ‘ on GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 5I indicated by apparent fragments of shells seen on polished surfaces amdeaim section, | returm these specimens fo you for your. ex- amination. I notice that one side of the rock specimen exposes something that suggests a head of Conocephalus or other primitive trilobite.” Figure 17 is a_ photomicro- graph of a section of this roc and shows what appears to be a fragment of a tiny shell. The microscope failed to bring out any structure in the concentric masses. In addition to the suggestive marking referred to by Doctor Clarke as possibly representing a trilobite cephalon, the writer. noted another strongly suggest- Fig. 17. Showing a thin section of the lime- stone in the floor of Ruppert’s quarry ing a Hyolithes. The rock layers in the floor of the quarry are about ten or twelve feet below the layers yielding L. pinniformzis and the whole are conformable. The Trenton. This horizon, as mentioned above, was reported by Professor Dwight from the eastern margin of the belt on the tanmoieow Re | Kimlin and was recognized by the presence of Solemopora compacta. No other localities have been described. Petrographic characters and further description. ~The Potsdam rock in the locality first reported by Professor Dwight was described as varying from a tough compact limestone through fissile, shaly argillaceous types and arenaceous and oolitic limestones, into quartz- itic varieties which were sometimes brecciated. All were calcareous. M@hese'may be verified for the most part. Whe calcareous quartzite is often friable from the loss of the carbenate and rusty from iron discoloration. It frequently carries shell-like depressions or molds. Along the western margin of this strip large quantities of sand are dug and shipped away for molding purposes. In appearance, it strongly suggests the rusty quartzitic phase of the Potsdam of this western strip. As favorable a place as any for observing this Sandeis (ome: tara or ivi Poel on the Camelot road north of Casper creek. A section beginning at the eastern margin of the belt, just south- east of R. J. Kimlin’s farm, and running west along the Spackenkill 52 NEW YORK STATE MUSEUM road to the Poughkeepsie road, and then continued to the river along the road to the molding sand dock a mile and a half north of Camelot, and thence along or just east of the track to Camelot station gives all the principal varieties of rock that have been met with north of Stoneco quarry. Beginning at the east, south of Kimlin’s farm, at the top of the hill on the Spackenkill road, the rock in the ledges is of a light steel-blue color and of medium grain (letter A in the section, fig. 18). PoTSDAN CR’s Quarry) 7 SHALY LimcsTone CHERTY Soreniee Fig. 18 Section along the Spackenkill road It often carries on fresh. surfaces markings of calcite, shaped like the segments of various curves, and blackened depressions and pits which have no particular or definite form. Just north of the junc- tion of the two roads at this point on the east side of the road that passes Kimlin’s house a brecciated conglomerate was noted re- sembling the Trenton as seen elsewhere in the quadrangle and carry- ing masses that resembled Solenopora compacta. The next cut west on the Spackenkill road shows many chertlike masses and scroll effects of silicilous material that have weathered out. North of here in the fields of Mr Mulkemus and in the neigh- boring woods the ledges carrying this variety of rock are very numerous and may be traced some distance east and west (let- tered B, fig. 18). This rock gives place, near and at the junction with the Varick road, to dull gray ledges of arenaceous limestone which has a coarse sandpaperlike appearance on weathered surfaces. One-fourth mile beyond this, rock outcrops on the north side of the road and lies quite flat (lettered CG, fig. 18). The rock at Ruppert’s quarry, one-fourth mile farther west (lettered D, fig. 18), in general character is almost identical with that of the two previous outcrops. The rock in the quarry varies in color from black to gray. The beds average thicker at the base and grow thinner toward the top. There are a few shaly layers. The strike of the quarry rock is about n. 75° e. and the dip about 10° northwest. At the corner of the Spackenkill and Poughkeepsie roads im- pure limestone outcrops on the east side of the latter road with 1Camelot station is at the point marked Stoneco on the map. The name Stoneco is usually applied to the Clinton Point Stone Company’s quarry, a mile below Camelot station. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 53 a strike of n. 23° e. and a dip of 70° s.e. This may belong with the slate formation and may therefore be on the downthrow side (let- tered F, fig. 18). Ledges of rock similar to that in Ruppert’s quarry occur to the southeast along the western margin of the belt, to the north and south of the first road leading to the river, and west of the road leading from this toward Camelot station. East of Camelot sta- tion, about roo feet up the hill, on the south side of the New Hamburg road, ledges of rock identical with that in Ruppert’s quarry strike approximately east and west and dip about 12° to the south. The first road leading to the river, south of the Spackenkill road, leaves the Poughkeepsie road (old Albany turnpike) one-fourth mile south of the schcolhouse. The river road gives off two branches, the shorter, lower one going to the dock of the White- head Sand Company and the other to Camelot station. On the east side of the lower road, just north of the red house, coarse conglomerate, familiar in Trenton localities within this quad- rangle, outcrops in one or two large ledges. This rock, in a brec- ciated condition, was also noted farther south along the upper road where this runs parallel with the railway track, about one-fourth mile north of Camelot station. Along the middle portion of this western strip the topography generally indicates a very gently sloping almost flat substratum of rock, and the extraordinary width of the belt is plainly due to the nearly horizontal position of the underlying strata for long distances. The varieties of rock described by Professor Dwight would seem to be accounted for mainly as outcrops across the dip of several beds showing variations of texture and composition, and partly to the different effects of weathering on these, as well as to possible frictional brecciation. The portion of the section which may be seen at Stonec ) in the quarry of the Clinton Point Stone Company is be- tween one-fourth and one- third of the breadth of the strip from its eastern margin and displays a thick mass of dolomitic limestone dipping gently to the west (see plate 8). For the most part it is thick-bedded. There are some thinner layers near the top and in the middle. Some beds carry numerous chertlike masses and in this particular, as well as in Fig. 19 Section at Stoneco quarry 54 NEW YORK STATE MUSEUM general character, the reck strongly resembles the variety described above along the Spackenkill road cn the farm of Mr Mulkemus near the eastern margin of the belt. No fossils were found in the beds of this quarry and hence no definite idea of its age could be obtained. Just east of Camelot station, as described above, arenaceous lime- stone identical with that in Ruppert’s quarry, dips to the south at an angle of 12°. This suggests a southward pitch and a superior position for the strata in the Stoneco quarry, a mile to the south of Camelot. The stratigraphic position and estimated thickness of the Stoneco beds agree with those of the cherty rocks along the Spackenkill road to the northeast. Presumably these strata once entirely covered the Upper Cambric (Potsdam) along the central and western portions of the strip and have been preserved at the south on account of the pitch of the series. ) Structural features. It is not possible to tell with absolute certainty what the exact relationships are among the different strata composing the series of this western strip. Presumably the Upper Cambric beds are followed conformably by those which apparently have a superior stratigraphic position. But in these latter strata it is necessary to recognize a probable interval of erosion as is in- dicated by relationships which can be determined with more exact- ness within the central strip and which is shown by the presence of a conglomeratic layer, even in this western belt. As will be discussed farther on this conglomerate, though possessing peculiar features, marks a change in fauna as well as in the lithic character of the rock and must be taken as marking a definite hiatus. The present almost horizontal position of the Upper Cambric and overlying beds theoretically admits of two explanations. It either represents a close overturned, recumbent fold, of else™a reversed fault accompanied by westward thrusting, which was pre- ceded by only relatively little folding. These rocks show no indications of extensive slickensiding, of compression of layers, or of flow structures such as would be ex- pected in violently folded strata. There is evidence of some brec- ciation and slipping in the rock along the eastern margin, but this is not severe. There is extensive fracturing which is, however, readily explained by the hypothesis of reversed faulting and thrust- ing. The field relations point to an upward movement of older strata into overlying younger ones similar to that already described for JSoM oY} 0} SuIddip sauojs -SUT] Popped APY 9Y} SurmoYys ‘Od9u0}G ‘AuRdUTOD 90S WTO Uo TTD) oy} Fo AdIvND oy} }v [[eM ysvoayyNos oy} Fo uos0d vy | 8 Id . GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 55 the gneisses. Along the western margin of the strip the compres- sion brought the Upper Cambric beds against the slates, which were first folded and overturned and then overridden. At the quarry at Stoneco and below Marlboro station across the river the west- ward dipping younger strata show a diminution in the upward thrust toward the southwest which may be associated with an earlier re- lease that elevated the Glenham belt. As already indicated, the conglomerate appears in places along the western margin of the strip. It is best interpreted as belonging with the downthrow block and is to be associated with the slate rather than with the limestone. It is likely that there was a strong horizontal component in the thrust that carried the older beds over the slates to the west of this strip. ~The conglomerate alcng the eastern margin would appear to occupy a normal position, but the fact that it is brecciated is note- worthy. ‘The presence of ledges yielding Lingulepis pinni- formis, as described above (see page 49), along the eastern margin in the near neighborhood of the Trenton, seems best ex- plained as an instance of faulting. The Potsdam beds seem clearly to have been overlain by younger strata, as is now the case at Stoneco quarry. It does not seem possible from the relationships exhibited elsewhere that the overlying strata were eroded so as to expose the Potsdam before the deposition of the Trenton. Apparently the limestone on the west of the Hudson is es- < sentially the continu- SE NW. AMIOMeOn this westery strip, but presumably the beds are younger even than those of the quarry at Stoneco.. Some of them resemble the beds of the central strip, as shown at the New Hamburg tunnel. On the west of the Hudson, near ie rivers. wedge vat Danskammer, the limestone dips to the southeast at an angle Ol Ose wlonge thie western margin, as shown just below Marlboro station, the dip is to the northwest. The limestones rest by overthrust on the slates at the west. Fig. 20 Section at Danskammer ae Fig. 2t Section below Marlboro station S.E,. 56 NEW YORK STATE MUSEUM Metamorphism and alteration. Brecciation has been noted along both margins of the strip. Fracturing has been extensive, pro- ducing many small cracks that have been healed by calcite. The broken surfaces of the rock along the eastern margin of the strip show by the smooth, distorted blackened depressions that there has been some movement in the rock. ‘The alteration is least where the beds are flattest. The principal changes then are due to granulation which usually has been sufficient to conceal or destroy organic remains. Summary. Presumably the Upper Cambric beds are followed » in this strip by the Beekmantown (Calciferous), as is the case in the central strip; but fossils belonging to this horizon have not yet been discovered. This terrane may be represented by all or part of the dolomitic strata shown in the Stoneco quarry and their apparent equivalents to the north. Locally about Saratoga a very fossiliferous limestone lens appears in the basal portion of the dolomite formation.” The trilobites discovered by Professor Dwight on the Spackenkill road, as mentioned on page 49, were like those discovered by Mr Walcott at Saratoga.® No fossils have been reported from the limestone on the western bank of the Hudson within this quadrangle. In 1879 R. P. Whit- field* reported Maclurea magna from these limestones at Newburgh and in 1880 W. B. Dwight® found an assemblage of Trenton fossils in that city. 1The description of the cherty, dolomitic limestone at the Stoneco quarry and overlying the Potsdam beds along the Spackenkill road was written in October I909. At the meeting of the Geological Society at Cambridge, Mass., the following December, Professors Ulrich and Cush- ing described a dolomite in the Mohawk valley which “is found to con- sist of two distinct formations, the lower a dolomite formation of Ozarkic age, the upper a limestone of Lower Beekmantown age with a distinct unconformity between the two.” The Beekmantown was described as thinning to the west, so that west of Little Falls the Lowville rests on the Ozarkic. The unconformity may be followed into the Champlain valley, reappears in the St Lawrence region “and is believed to mark the line of division between the two formations everywhere in northern New York.” 2Preliminary list of papers. G. S. A., 22d winter meeting at Boston- Cambridge, December 1900. 3 See Thirty-second Ann. Rept. N. Y. State Mus.; also U. S. G. S. Bul. 30, p. 21, and Science, 1884, 3 :136-37. 4 Amer. Jour. Sci., Ser. 3, 18:227. 5 Amer. Jour. Sci., Ser. 3, 19 :50-54. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 57 EE CE INGA 2 oi REP Boundaries. This strip enters the quadrangle from the north at Pleasant Valley. Its eastern margin forms the western bank of Wappinger creek north of the covered bridge at Pleasant Valley and southward follows the creek closely as far as Rochdale. At this place the limestone is in contact with the slate at the dam and on the island just below it. South of Rochdale the limestone fol- lows the creek for one-half mile and then bears slightly to the west. It apparently ends just north of the terrace one-fourth of a mile east of Tompkins’s house (see plate 17) on the Pleasant Valley road.: This terrace fringes an old meander of the creek and extends around to the south side where the limestone appears again just south of the road that skirts its edge. East of the portion of this road run- ning north and south, just west of Frank De Garmo’s house, are numerous outcrops of the slates, but these disappear at the terrace slope and no outcrops appear in the deep westward embayment formed by the old meander. This embayment is regarded as lying in a zone of transverse faulting. It seems probable that the slates were dropped down in here. At any rate, either on this account or because of faulting, a weakness was produced which the base-leveling forces caught and finally left as a gap in the ridge of limestone. It seems probable from the dimensions of certain faulted limestone blocks a short dis- tance to the eastward that they belong in or near this gap. The slate has been dropped between the faulted masses and the dis- membered main strip. South of the break in the central strip its eastern margin follows the road until the latter turns eastward and then extends as a con- spicuous wooded scarp in a north and south line to a point about one-third of a mile south of Frank De Garmo’s house. At this point the limestone sends a sharp angular spur eastward for about 200 yards, as shown on the map. The strike of the slates just west of De Garmo’s house, projected southward, would bring them sharply against the limestone in the included angle of this spur, showing a transverse fault between the slates and the spur and indicating that the eastern marginal scarp south of De Garmo’s is a faulted one. Limestone outcrops at the apex of this spur, whence it may be traced by continuous outcrop along the margin of the slate to and across the railroad track and highway west of Manchester Bridge. South of here the eastern margin follows the eastern base of an immense drumlin and south of this distinctly to the Poughkeepsie- 8 NEW YORK STATE MUSEUM ot New Hackensack road; then across this and fer a short distance to the south. ‘The margin is then apparently broken by a spur in a manner similar to that just described, although this time the break appears to be along an extensive fault line. The slates which out- crop south of the Poughkeepsie-New Hackensack road and west of the cross road that leads from it to the Spackenkill road, lie in the included angle of this spur. The contact is then easily followed southward by the steep mar- ginal scarp in the limestone, from the point where the cross road just mentioned makes its turn, to and across the Spackenkill road, and east of the old Boardman farm. The gully which, as shown on the map, cuts across this central strip west of the northern termination of the narrow faulted strip lying on the east, may represent a fault. South of the Spackenkill road slates outcrop in numerous places between the main strip and the narrow faulted mass just east and south through the swamp to the southern end of the small strip, leaving no doubt but that, at the surface, the two limestone masses are separated by a narrow band of the siates. The eastern contact is then very readily followed through the fields to Channingyville and then less distinctly under the drift between the creek and the New Hamburg road to the bank of Wappinger creek near its junc- tion with the Hudson. The western margin of the central strip could be determined with much more exactness in certain places than in others. At the north the surface deposits conceal it for the most part, but swamps and other topographical features and oc¢asional outcrops enable one to follow it approximately, and in a few places distinctly, until it crosses the Pleasant Valley road just west of Rochdale. The lime- stone then forms a distinct scarp east of the road to the break just southeast of Tompkins’s house. South of this the margin is distinct to the railroad, but across this it is soon lost under the drift com- posing the large drumlin at this point. The limestone reappears on the south side of this hill and again a little farther south as a scarp which crosses the Poughkeepsie-New Hackensack road. South of this road the margin is readily followed, often with the limestone and slate in close proximity, to the Poughkeepsie-Wap- pinger Falls road which, going south, ascends the western scarp of the limestone. South along the New Hamburg road the contact is clearly for a distance on the east side of the road as the slate was noted in the latter. But along here the kame deposits effectually conceal the exact relationships between the limestone and slate. At the northern end of the New Hamburg tunnel the limestone rests GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 59 by overthrust upon the slate (see plate 9) and occasionally the limestone outcrops along the slope to the northeast for a short distance. _ Terranes present. The Potsdam, Beekmantown (Calciferous- Rochdale group) and Trenton horizons have been identified along this central strip within the quadrangle. The Potsdam. This horizon was first noted in this strip just _ a little north of the quadrangle boundary half way between Pleasant Valley and Salt Point At Pleasant Valley Lingulepis pin- niformis was reported along or near the western margin of the strip to the northwest of the village in rather characteristic argil- laceous limestone, and also from some hills to the north of the vil- lage between the old Poughkeepsie and Eastern Railroad bed and Wappinger creek.2 At the latter place the beds carrying L. pinni- formis also had small brachiopods, apparently Orthis and Tri- plecia, as well as minute gastropods, fragments of trilobites and Opimileta compacta. These beds were mixed with Calci- _ferous and Trenton strata carrying other fossils characteristic of these limestones in this region. The Potsdam was identified near Rochdale, just west of the Poughkeepsie-Pleasant Valley road. The beds exposed in the quarry just northwest of Alson De Garmo’s house, from which stone was removed for the State road, are pos- sibly of Upper Cambric age. A search for fossils in this quarry was unrewarded. In a note to his paper on the discovery of Pots- dam fossils in Poughkeepsie, south of the driving park, as described for the western strip, Professor Dwight* mentioned the discovery of a fragment of brachiopod shell which he believed to be that of Miran leopis pinwitormis ma rock very similar to that at the locality south of the driving park. He described this new locality as about one-half of a mile south of the Boardman mansion on the Spackenkill road, but it is uncertain from his description at just what point the fossil was found. The Beekmantown (Calciferous-Rochdale group). In Jan- -uary 1880, Professor Dwight* reported the discovery of a rich assemblage of fossils of Pretrenton age at Rochdale, a small fac- tory hamlet four miles northeast of Poughkeepsie. Wo be Dwight Amer jour Scr, July, 1881, 34:27—-32. 2(W. B. Dwight) J. M. Clarke. Guide to the Fossiliferous Rocks of New York State. N. Y. State Mus. Handbook 15, p. 9-10. 3 Amer. Jour. Sci, Feb. 1886, 31 :136. 4 Amer. Jour. Sci., January, 1880, 19:50 et seq. 60 NEW YORK STATE MUSEUM The following named fossils were enumerated as the most ‘im- portant: “Ophileta complanata (possibly Ophileta\ come pacta), ©. levata, ©: > sordida ~ Qlacltiieawo aa: dida), Orthoceras primigenium.” OthemMunivalge: were noted but not identified. A network of “ fucoidal fronds ” might be Bythotrephis antiquata. The fossils of the neighboring Trenton at the east were absent from this rock and it was believed to lie beneath the Trenton, both strata having an east- ward dip. It was called the Calciferous.' In October 1880, Dwight? found at the Rochdale locality another remarkable assemblage: “ great numbers of Orthocerata and other fossils, many of which are not reported as occurring in New York State.” In lithology this rock was identical with that previously assigned to the Calciferous. Orthocerata were abundant and dis- coidal gastropods very plentiful. In addition to its own peculiar fossils, it contained the “ fucoids”’ and other types of the adjacent Calciferous. Dwight hesitated to announce the exact stratigraphical position of this new fossil assemblage. The wealth of cephalopods separated it very sharply from any other known terrane in the United States below the Black River-Trenton, to which it was in- ferior. In its numerous orthoceratite cephalopods it resembled the Quebec group of Canada. In 1882 Diwght® reported tracing the Calciferous in this strip to a point five miles below Poughkeepsie. In addition to the above- named *‘ Calciferous ” fossils he announced in this paper: A large Holopea and smaller ones not identified, many Pleurotomaria re- sembling Canadian forms, a minute Ophileta n. sp., a Mur- chisonia resembling gracilis of the Trenton, one or two orthides, many undeterminable fragments of Bathyurus, Chaetetes ly- coperdon var. ramosa, not hitherto reported below the Tren- ton, 25 to 30 species of Orthocerata, all apparently new in the United States, two species of Lituites and a Cyrtoceras. In 1884* a number of these fossils were described with figures; trilobite frag- ments were provisionally assigned to the genus Bathyurus (B. 1 The ledges at the summit of the hill north of Alson DeGarmo’s house on the Pleasant Valley road belong, in part at least, to Dwight’s Calci- ferous locality. 2 Amer. Jour. Sci. Ser. 3, 21:78. 3 Proc. Amer. Assoc. Adv. Sci. (Montreal meeting), v. 31. Abstract Aug. 1882, p. 3-6. . 4 Amer. Jour. Sci., Ser. 3, April, 1884, 27 :249-59. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 61 taurifrons and B. crotalifrons). New cephalopod species wiene described as Cyrtoceeras vassarina, C. ? dacty- fomates CC. microscopicum, Orthoceras apissi- fomedim:) O: henrictta, Oncoceras vassifiorme. In 1900 Dwight! designated the main Calciferous strata as the Cyrtoceras vassarina beds and called attention to the great persistence for a distance of nearly thirty miles in the Wappinger limestone, of a layer which contains a fauna quite different from that of the main beds. It lacked cephalopods entirely. There were no important fossils in common in the two beds except two or three always present in the Calciferous. In some respects it resembled the Fort Cassin of Vermont, but differed in the extreme scarcity of eepmalopods, ihe presence of Lingulepis pinniftormis suggested a low horizon in the Calciferous. What Dwight has called a low horizon in the Calciferous may be Upper Cambric discon- formably overlain by Beekmantown. The Trenton. Fossils belonging to this horizon were the first to be discovered in the Dutchess county limestone und were hrst reported from the area within this quadrangle. Mather referred only in a footnote to their having been found in a quarry south of Pleasant Valley by Professor Briggs. His assign- ment of the age of this formation was based on fossils found in the beds of limestone within the slate formation a mile or so north of Barnegate. In 1879 Professor Dwight? found the following Trenton fossils fapnoccidaic: Weptaecna (Rlectambonites ) sericea, Oraiisstricenaria, Receptaculites sp. A week after the discovery Dwight and Dana visited this locality. The following i@eciismmere found: Ika (PrP) serreea HE sehatr apo ait ec ta, pibodictya acuta, the caudal shield of a trilobite probably, PEE us wetwshis, Orthis tricenaria, \O! pec mmella, ©, testudinaria, an- Endoceras, an’ Orthoceras: specimens of Chaetetes, and encrinal columns.? On this same excur- sion the quarry south of Pleasant Valley, mentioned by Mather, was visited. A fossil assemblage very like that at Rochdale was at once discovered. Subsequent examination of this collection HoOWcda mo epopmonmena alternata © fragments: file Chaetetes was named by Dwight C. tenuissima. D Bul Geol. Soc. Amer, v. 12) 1900, abstract. 2;Amer. Jour. Sei May, 1870, 17 :380. emer, our Sin i \Wlayasis70; «17300, See also p-138t- 62 NEW YORK STATE MUSEUM In 1880 Professor Dwightt added to the above from the Roch- dale locality: a number of cyathophylloid corals, among them Petraia corniculum, a head of Echinoencrintees anatiformis, and the caudal shield of a trilobite identified as Eilaenus (‘crass veanid a. The C. ténwisis timate identified as in part at least, Stromatopora compaena Billings (Chaetetes compacta Dawson). This tess now recognized as Solenopora compacta. The Trenton also occurs at Pleasant Valley in the railroad cut just east of the Central New England station on the old Pough-. keepsie and Eastern road. The Trenton beds here have yielded Tetradium cellulosum and great numbers of entomostraca and fragments of small trilobites.2 The characteristic Trenton con- glomerate carrying Solenopora compacta occurs at the northeast end of the cut. The Trenton apparently has an extension eastward in the village. The conglomerate carrying fossils was noted by the writer at the hose house. It is quite probable that other Trenton localities in later years were noted by Professor Dwight which were never published. Petrography and further description. Beds from this strip, which have been referred to the Potsdam, vary from argillaceous to arenaceous limestones with occasional shaly layers. It is not pos- sible to say much about the extent of the Potsdam along this strip to the south. It may occur at many places for which, however, there is at present no paleontologic evidence. ‘The structural features suggest that it is probably confined to the northern and central por- tions of the strip and that the beds at the south are probably younger The shaly limestones in the quarry west of the tunnel at New Hamburg have been thought to be of Potsdam age on stratigraphic grounds. The Beekmantown (Calciferous) of this strip is best studied at its type locality at Rochdale. It is often, 1f not characteristically, arenaceous and varies in color from a bluish gray to a gray with lighter chamois-colored layers which weather very white. The two are interstratified, though the writer's observations indicate that the bluish beds are usually near the eastern margin and therefore in the upper layers. The bluish beds carry grayish wavy markings and are very tough and splintery, breaking with conchoidal fracture. 1 Amer. Jour. Sci., v. 19, January 188o. 2(W B. Dwight) J. M. Clarke. Guide to the Fossiliferous Rocks of New York State. N. Y. State Museum Handbook 15. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 63 The lower portion of the Calciferous shows many thick, grayish layers in places. Apparently the Beekmantown has a wide distribution in this strip. It forms the main mass of the high hill northwest of the Trenton in the cut at Pleasant Valley and may be traced rather satisfactorily as a lithic unit to Rochdale, where it 1s seen to have a great thickness, estimated at from 1000 to 1200 feet. Dwight claimed to have traced it definitely to a point five miles below Poughkeepsie (see above). The beds resting on the slates at the New Hamburg tunnel are probably of Beekmantown age. At Rochdale the Beekmantown in places passes through a heavy conglomerate into the Trenton which rests upon it. Just a little way south of a ledge of this conglomerate on the property of Henry Titus. along the road, are fine exposures of the bluish-gray beds. These give place at the west to the gray and dove-colored beds which compose most of the hill between Rochdale and the Pleasant Valley turnpike. The bluish-gray beds were noted farther south near the eastern margin just north of the break in this strip. Taking the apparent _ thickness at Rochdale as a guide, the beds intervening between these biue beds and the scarp just east of Tompkins’s house are probably all Beekmantown. South of here the lithology does not convey very much, though indicating on the whole the southward continu- ation of the lower portion of the Beekmantown as shown at Roch- dale. Within this strip farther south, about one-fourth mile north of the Spackenkill road, along an old wood road, or cow path, are probable beds of the Beekmantown within a few rods of coarse Trenton conglomerate apparently carrying Solenopora com- Daeta, Whe road from the orchard on the north side of ‘the Spackenkill road, opposite the old Boardman farm, leads to these outcrops. ‘This locality is seemingly not so far south as Professor Dwight claimed to have traced the Beekmantown; but the writer has not been able to add anything definite to the age of this belt to the south of this point. The Trenton, within this strip, is usually a dark blue rather crystalline rock of quite different appearance from the Beekman- town. Its lower portion is conglomeratic and carries colonies of the coral S. compacta which, without careful examination, might be taken for pebbles. This coral, or a conglomerate appear- ance, is often the only means for identifying this member of the limestone formation. The Trenton is also somewhat finely con- glomeratic at times. The conglomerate was noted at Pleasant 64 NEW YORK STATE MUSEUM Vailey, at Rochdale and north of the Spackenkill road. - The Trenton also is probably present in places not yet discovered along the eastern margin of this strip. At Rochdale the dark blue Trenton beds have a thickness apparently between 60 and 100 fee and i a conspicuous stratum. Strikes and dips within this strip show much uniformity. In the Poughkeepsie and Eastern Railroad cut at Pleasant Valley the Tren- ton beds show a strike about n. 37° e. and a southeast dip. In the quarry on the Pleasant Valley road to the west of Rochdale the sup- posedly Potsdam beds strike n. 42° e. and dip 60° to the southeast ; at Rochdale in the road near the mill site, the strike is n. 40° e. and the dip 55° southeast; at the conglomerate ledge on the Titus place approximately n. 43° e. and 58° s.e.; at the eastern margin east of Tompkins’s n. 28° e. and 35° southeast; north of the Spacken- kill road in the woods near the old barn n. 53° e. and 42° s.e.; at the New Hamburg tunnel about n. 60° e. and 30° s.e. Structural features. The presence of an €roSiom) jimteage! between the Trenton beds and the Beekmantown is conclusively shown by the relationships at Rochdale. The Beekmantown is separated from the Trenton by a heavy conglomeratic layer, and the fauna and lithologic character of the two strata are markedly dif- ferent. The general uniformity of dip shows a “ deceptive uncon- formity”’ or “disconformity.’? From the apparent thickness of the Beekmantown at Rochdale, it would seem that this formation was not extensively eroded here. The limestones of this central strip rest against the slates on the west by overthrust. This is best shown at the north end of the New Hamburg tunnel (see plate 9). The occurrences of the Potsdam along this western margin is also evidence of it. Fre- quent slips along and across the strike within the limestone are probably present. The slates along the eastern margin of the strip may be at places in conformable relationship with the limestone. In other cases such is almost certainly not the case. Metamorphism and alteration. The strata composing this strip are all visibly altered. Fossils have usually been greatly obscured. The Beekmantown shows the metamorphism most. Fossils in it are recognized or identified usually with difficulty although they sometimes weather out with distinctness. The Tren- ton beds are usually somewhat crystalline, but fossils are preserved in them in better condition than in the Beekmantown. 1 Professor A. W. Grabau. Science, n. s., 22 :534. Juuny SINQUIV FT MIN IY} FO Pus ULOYJIOU IY} Je Sope[S IY} UO JSNAIYIIIAO SoUc SOUT = : rh GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 65 Summary and conclusion. The absence of the Trenton con- glomerate at places along the eastern margin of the central strip might be interpreted as the result of faulting and, in any event, is probably due in part, at least, to faulting. The presence of Tetradium cellulosum in the Pough- keepsie and Eastern Railroad cut at Pleasant Valley is noteworthy. Professor Clarke! has indicated that elsewhere this fossil 1s charac- teristic of the Lowville. The Trenton conglomerate at this locality is apparently a few feet above the beds carrying this fossil. This would seem to indicate that the Lowville might have been deposited here. Doctor Ruedemann? has discussed the Trenton, as descrbed by Dwight, as probably not lower than Midtrenton in age. The examination of this strip leaves one in great doubt as to how to represent its structure. It is certainly very different from Pro- fessor Dana’s early representation as a simple fold.* It is best inter- preted as belonging to the same thrust that pushed the western strip on the slates, but as the map shows the limestone broke both along and across the strike and at the south was pushed farther west, apparently feeling the influence of the Highlands mass. MISCELLANEOUS FAULTED BLOCKS OF THE WAPPINGER CREEK BELT Several smaller limestone masses, each of which can be reason- ably shown to be a detached and separate block, forming an inlier in the slates, are scattered to the east of the central strip along its middle portion. The mantle of the surface deposits at times greatly obscures their exact relationships to the slates, but as a rule the field relations leave scarcely any doubt of their inlying character. In most, if not all cases, these relations point to faulting, both along and across the strike between the limestone masses and the slates which surround them. These blocks will be described separately and will be designated by numbers from north to south. The occurrence of these faulted blocks of limestone to the east of the central strip seems to be -directly due to the thrust which carried the limestone of this belt over the slates. They have been left, stranded as it were, behind the main mass. 1 Guide to the Fossiliferous Rocks of New York State. N. Y. State Mus. Handbook 15, p. 9. 2 Hudson River Beds near Albany and their Taxonomic Equivalents. NEY state Mus: Bul 42500n,