*6 • OT/X- -mo. 33! LIBRARY New york botanical New York State Museum Bulletin Published by The University of the State of New York No. 331 ALBANY, N. Y. December 1942 NEW YORK STATE MUSEUM Charles C. Adams, Director GEOLOGY OF THE CATSKILL AND KAATERSKILL QUADRANGLES PART I CAMBRIAN AND ORDOVICIAN GEOLOGY OF THE CATSKILL QUADRANGLE By Rudolf Ruedemann Former State Paleontologist , New York State Museum GLACIAL GEOLOGY By John H. Cook Temporary Geologist, New York State Museum ECONOMIC GEOLOGY By David H. Newland Former State Geologist, New York State Museum CONTENTS FAGE Preface 7 Physiography 8 Relations of geology and topog- raphy to flora, fauna and hu- man culture of region 26 Descriptive geology 37 Cambrian system 37 Canadian system 78 Ordovician system 88 Silurian and Devonian strata of Becraft mountain 124 Structural geology 132 Overthrusts 139 Normal faults, Cross faults 142 Folding 145 Boudinage and Cleavage 150 PAGE Metamorphism 157 Age of folding and thrusting. . . .160 Historical geology 171 Precambrian history 175 Cambrian history 176 Canadian and Ordovician history.180 Silurian history 181 Devonian history (see Chadwick, Part 2) 182 Carboniferous history 186 Mesozoic history 187 Cenozoic history 187 Glacial geology by John H. Cook . . 189 Economic geology by David H. Newland 239 Bibliography 242 Index 249 ALBANY LD CD CL- UJ CO M360r-Je 41-2000 THE UNIVERSITY OF THE STATE OF NEW YORK 1942 Digitized by the Internet Archive in 2017 with funding from IMLS LG-70-15-0138-15 https://archive.org/details/newyorkstatemuse3311newy New York State Museum Bulletin Published by The University of the State of New York No. 331 ALBANY, N. Y. December 1942 NEW YORK STATE MUSEUM Charles C. Adams, Director GEOLOGY OF THE CATSKILL AND KAATERSKILL QUADRANGLES PART I CAMBRIAN AND ORDOVICIAN GEOLOGY OF THE CATSKILL QUADRANGLE By Rudolf Ruedemann Former State Paleontologist, New York State Museum GLACIAL GEOLOGY By John H. Cook Temporary Geologist, New York State Museum ECONOMIC GEOLOGY By David H. Newland Former State Geologist, New York State Museum CONTENTS PAGE Preface 7 Physiography 8 Relations of geology and topog- raphy to flora, fauna and hu- man culture of region 26 Descriptive geology 37 Cambrian system 37 Canadian system 78 Ordovician system 88 Silurian and Devonian strata of Becraft mountain 124 Structural geology 132 Overthrusts 139 Normal faults, cross faults 142 Folding 145 Boudinage and cleavage 150 PAGE Metamorphism 157 Age of folding and thrusting. . . .160 Historical geology 171 Precambrian history 175 Cambrian history .* 176 Canadian and Ordovician history. 180 Silurian history 181 Devonian history (see Chadwick, Part 2) 182 Carboniferous history 186 Mesozoic history 187 Cenozoic history 187 Glacial geology by John H. Cook. .189 Economic geology by David H. Newland 239 Bibliography 242 Index 249 THE UNIVERSITY OF THE STATE OF NEW YORK 1942 THE UNIVERSITY OF THE STATE OF NEW YORK Regents of the University With years when terms expire 1943 Thomas J. Mangan M.A., LL.D., Chancellor Binghamton 1945 William J. Wallin M.A., LL.D., Vice Chancellor - - - Yonkers 1950 Roland B. Woodward M.A., LL.D. - -- -- -- - Rochester 1951 Wm Leland Thompson B.A., LL.D. - -- -- -- - Troy 1948 John Lord O’Brian B.A., LL.B., LL.D. ------- Buffalo 1952 Grant C. Madill M.D., LL.D. Ogdensburg 1954 George Hopkins Bond Ph.M., LL.B., LL.D. Syracuse 1946 Owen D. Young B.A., LL.B., D.C.S., L.H.D., LL.D. - - New York 1949 Susan Brandeis B.A., J.D. - -- -- -- -- -- New York 1947 C. C. Mollenhauer LL.D. - -- Brooklyn 1944 Gordon Knox Bell B.A., LL.B., LL.D. - New York 1953 W. Kingsland Macy B.A. - -- -- -- -- -- Islip President of the University and Commissioner of Education George D. Stoddard B.A., Ph.D., LL.D., Litt.D. Deputy and Associate Commissioner (Finance, Administration, Vocational Education) Lewis A. Wilson D.Sc., LL.D. Associate Commissioner (Instructional Supervision, Teacher Education) George M. Wiley M.A., Pd.D., L.H.D., LL.D. Associate Commissioner (Higher and Professional Education) J. Hillis Miller M.A., Ph.D., Litt.D. Counsel Charles A. Brind jr B.A., LL.B., LL.D. Assistant Commissioner for Research J. Cayce Morrison M.A., Ph.D., LL.D. Assistant Commissioner for Teacher Education Hermann Cooper M.A., Ph.D., LL.D. Assistant Commissioner for Personnel and Public Relations Lloyd L. Cheney B.A., Pd.D. Assistant Commissioner for Finance Arthur W. Schmidt M.A., Ph.D. Assistant Commissioner for Instructional Supervision Edwin R. Van Kleek M.A., Ph.D. Assistant Commissioner for Professional Education Irwin A. Conroe M.A., LL.D., L.H.D. Assistant Commissioner for Vocational Education Oakley Furney B.A., Pd.M. State Librarian Robert W. G. Vail B.A. Director of State Museum Charles C. Adams M.S., Ph.D., D.Sc. State Historian Arthur Pound B.A., L.H.D. Directors of Divisions Adult Education and Library Extension, Frank L. Tolman Ph.B., Pd.D. Elementary Education, William E. Young M.A., Ph.D. Examinations and Testing, Harold G. Thompson M.A., LL.D. Health and Physical Education, Hiram A. Jones M.A., Ph.D., D.Sc. Higher Education Law, Joseph Lipsky LL.B. Motion Picture, Irwin Esmond Ph.B., LL.B. Research, Warren W. Coxe B.S., Ph.D. School Buildings and Grounds, Gilbert L. Van Auken, B.Arch. Secondary Education, Warren W. Knox M.A., Ph.D. LIST OF ILLUSTRATIONS PAGE Figure 1 View across the Hudson River plain looking west from Plass hill frontispiece Figure 2 Blue hill, a chert monadnock, seen from southeast 11 Figure 3 Mt Merino, a chert monadnock, seen from northwest 12 Figure 4 Unconformity at Jonesburgh quarries, Becraft mountain IS Figure 5 Twin pond in kettle hole, Elizaville 19 Figure 6 Warackamac lake, a typical kettle hole, Cokertown 20 Figure 7 Early stage of Susquehanna drainage in Mesozoic time 23 Figure 8 Diagram of physiography of Catskill quadrangle 25 Figure 9 Northernmost station of prickly pear in Hudson valley, Mt Merino 31 Figure 10 Ledge of chert with growth of red cedar, east of Blue hill 33 Figure 11 Young forest of red cedars upon chert plateau, east of Blue hill 34 Figure 12 Nassau phyllite near Jacksons Corners 39 Figure 13 Further enlargement of Nassau phyllite 40 Figure 14 Chart showing locations and vertical sections of iron mines near Hudson 44 Figure 15 Adits of the old Mt Tom mine 47 Figure 16 Diagram of section at Mt Tom mine 49 Figure 17 Abandoned workings and adit of former Plass Hill mine 51 Figure 18 Contact of Nassau beds and Burden iron ore in Greendale road section 52 Figure 19 Schodack limestone in Greendale Road section 55 Figure 20 Thin section of Burden iron ore 56 Figure 21 Diagram of Greendale Road section 59 Figure 22 Section of Schodack beds along road south of Elizaville 67 Figure 23 Section of Cambrian and Ordovician along road southwest of Bingham Mills 69 Figure 24 Schodack beds in Fishers quarry 71 Figure 25 Enlargement of lens of edgewise conglomerate in Fishers quarry 72 Figure 26 Road cut on Highway 9, showing lenses of edgewise conglom- erate; Schodack beds 73 Figure 27 Enlargement of two lenses of same 74 Figure 28 Diagram of section in road cut 75 Figure 29 Ash Hill quarry, Mt Merino 83 Figure 30 Deepkill chert along Mt Merino road 84 Figure 31 Photomicrograph of Normanskill chert showing dolomite rhombs 91 Figure 32 Photomicrograph of Deepkill chert crystallized into fine- grained quartzite 91 Figure 33 Photomicrograph of Normanskill red chert with radiolarians . . 92 Figure 34 Photomicrograph of crush-brecciated radiolarite with radio- larian spicules 92 [3] 4 ILLUSTRATIONS PAGE Figure 35 Diagram showing distribution of Normanskill chert and grit. . 93 Figure 36 Top of anticline in Normanskill grit in Austin glen 103 Figure 37 Broome Street quarry in Normanskill grit, South Catskill 104 Figure 38 Normanskill grit bedding plane with mud pebbles, Broome Street quarry 105 Figure 39 Alternating Normanskill grit and shale along New York Cen- tral Railroad, Linlithgo 106 Figure 40 Crest of overturned pitched anticline along New York Central Railroad, Rhinecliff 109 Figure 41 Syncline with fault along New York Central Railroad, North Germantown HO Figure 42 Large anticline with accessory smaller anticline along New York Central Railroad, North Germantown Ill Figure 43 Compressed, recumbent anticline along New York Central Railroad, North Germantown 112 Figure 44 Asymmetric overturned anticline in Normanskill grit, Catskill. 113 Figure 45 Rysedorph polymikt conglomerate at Mt Merino road 121 Figure 46 Enlargement of same 122 Figure 47 Ledge of Rysedorph conglomerate near Elizaville 125 Figure 48 Schodack-Manlius contact at Hudson 126 Figure 49 Thrust in Devonian strata at south end of Becraft mountain. . . 133 Figure 50 Diagram of formations in three supposed troughs of upper and middle Hudson valley 136 Figure 51 Section through southern part of Catskill quandrangle 140 Figure 52 Normal fault in Mt Merino quarry 143 Figure 53 Sharp zigzag folding in Mt Merino quarry 147 Figure 54 Steeply overturned broken anticline in Normanskill chert, south of Rip Van Winkle bridge approach 148 Figure 55 Section through Mt Merino and Becraft mountain 149 Figure 56 Nassau phyllite and quartzite showing bedding and cleavage.. 151 Figure 57 Quartzite bed in Nassau phyllite with boudinage fracture near Elizaville 152 Figure 58 Boudinage structure on Roeliff Jansen Kill road 153 Figure 59 Enlargement of same 154 Figure 60 Diagram of structure seen in figure 59 155 Figure 61 Diagram of successive stages in buckling 155 Figure 62 Vertical section through layers with boudinage 156 Figure 63 Schist with disjointed quartzite cemented with quartz 156 Figure 64 The St Lawrence and Acadian geosynclines in their original position 162 Figure 65 The structural units of the St Lawrence and Acadian geosyn- clines in their present position 164 Figure 66 Section through Mt Tom to Bell pond 177 Figure 67 Sketch of Burden iron ore belt 178 Figure 68 Diagram showing topographic relations at southern end of the “Albany clay” district 192 Figure 69 Diagram showing superglacial drainage from Niverville plain west of Kinderhook lake to the pools in which deposits form- ing the 250-foot terrace were made 198 ILLUSTRATIONS 5 PAGE Figure 70 View from ice-contact of a 270-foot terrace, northwest across the Roeliff Jansen valley near the mouth of Doove kill 205 Figure 71 Gravel ridge west of Maplewood Camps 206 Figure 72 Close-up view of gravel pit in ridge shown in figure 71 206 Figure 73 Looking north from the ridge shown in figure 71 207 Figure 74 Cherry Hill pond and environs, looking southwest to Blue hill from a steep ice-contact 211 Figure 75 Explanatory diagram of figure 74. 211 Figure 76 Part of the Koettlitz glacier, South Victoria Land, Antarctica. 215 Figure 77 Sketch map showing that the residual ice directed lines of superglacial drainage southward out of the Roeliff Jansen Kill basin 219 Figure 78 Diagram of ice-confined terraces at the southeastern corner of the Catskill quadrangle and the Shook’s Pond terrace west of Rock City 221 Figure 79 Diagram showing delta fan north of Blue Stores 229 Figure 80 Diagram showing delta fans north of Bell pond... 230 Figure 81 Ice-contact slope east of the Potts Memorial Hospital 231 Figure 82 Bell pond and Manor hill 231 Geologic map .In pocket at end • r . ■ . . ■ - Figure 1 View across the Hudson River plain looking west from Plass hill south of Church hill. One sees in front the broad river plain (Albany peneplain), the stream bed being hidden except in the right corner. On the other side of the river plain the Helderberg plateau with the level surface of the Tertiary peneplain is seen. Above it rise the Catskills. In the river plain are wooded strips, marking rock ledges or creeks and orchards, often located on drunilins. (E. J. Stein photo) Part I CAMBRIAN AND ORDOVICIAN GEOLOGY OF THE CATSKILL QUADRANGLE By Rudolf Ruedemann PREFACE The mapping of the Cambrian and Ordovician formations of the eastern portion of the Catskill quadrangle, also of the Silurian and Devonian formation in the Becraft Mountain outlier, was undertaken at the request of Dr G. H. Chadwick who has mapped the western Devonian belt of the quadrangle, as well as the adjoining entirely Devonian Kaaterskill quadrangle. The work was also undertaken in the hope that problems that had remained undecided in the Saratoga-Schuylerville and Capital District bulletins would be cleared up by a study of the region to the south, especially as Dr Winifred Goldring had taken up the mapping of the Coxsackie quadrangle, directly between the Albany and Catskill quadrangles. It was hoped that T. Y. Wilson could at the same time map the Kinderhook quad- rangle, thus completing the group of quadrangles directly south of the Capital District. The writer has had in the mapping and study of the formations the frequent assistance of Dr Winifred Goldring and T. Y. Wilson to whom he is greatly indebted for their interest in the problems encountered. To E. J. Stein, Dr Winifred Goldring, J. W. Graham and the New York Central Railroad Company, the writer also wishes to make acknowledgment for most of the photographs. To Dr Homer D. House, state botanist, and Dr Rogers McVaugh of the U. S. Department of Agriculture, Washington, D. C., who for several years has been studying the plant ecology of the Hudson valley the writer is under obligation for information freely given on the flora of the region. Doctor McVaugh has been kind enough to write the chapter here incorporated in the physiography. Walter J. Schoonmaker has contributed data on the fauna. [7] 8 NEW YORK STATE MUSEUM PHYSIOGRAPHY The Catskill quadrangle extends north from 42° latitude to 42° 15' and west from 73° 45' western longitude to 74°. On the whole it is a sector from the Hudson River valley just east of the Catskill mountains which here rise in a 2000-foot wall to heights of more than 4000 feet not more than ten miles from the river bank. Below this great mountain massif extends the Helderberg plateau which rises from the river plain 300 to 400 feet in a steep escarpment that extends from north-northeast to south-southwest near the western margin of the quadrangle at a distance varying from one-half to two miles from the river bank. The river, here an estuary that extends above Albany to Troy, is about three-quarters of a mile wide. The river bed is entrenched about 100 feet on either side in rock cliffs and clay beds and lies in the river plain proper which extends westward with an average height of 200 feet to the foot of the Helderberg escarpment and eastward with the same average height about seven miles to the foot of a plateau that is seen in the southeast corner of the quadrangle, its edge extending southwest from Pine Hill (see Copake sheet) near Livingston through Elizaville and the Spring lakes. This plateau that, as we shall see, is largely caused by slight metamorphism resulting in greater hardness of the rocks, as well as overthrusting, and that we will therefore call the phyllite plateau, rises along the edge 300 feet above the river plain to 500 feet and gradually farther eastward beyond the quadrangle (on the Copake quadrangle) to 1000 feet. This plateau which also strikes northeast and which is nine to ten miles wide is rather abruptly followed by a broad depression, the so-called Harlem valley through which the Harlem branch of the New York Central Railroad passes. It is three to four miles wide and averages 600 feet in height, above sea level. Beyond this rises abruptly the Taconic Mountain range in peaks above 2000 feet such as Alexander mountain (2243 feet) on the Copake quadrangle. This mountain range forms the New York-Massachusetts boundary. The Silurian-Devonian rock series of the Helderberg plateau reached once across the river east to an unknown distance, but undoubtedly far beyond the Catskill quadrangle. An outlier known as Becraft hills in the northeastern corner of the quadrangle shows the former presence of these rocks on the east side of the river. There are thus recognizable a series of levels, one the Hudson River lowland, 100-200 feet high, and ten miles wide, beyond this GEOLOGY OF THE CATSKILL QUADRANGLE 9 on the west side the more or less reduced Helderberg plateau rising from 400 feet above the Hudson River plain or lowland at the escarpment to 700 feet at the foot of the 2000-foot wall of the Cats- kill escarpment (see figure 1). In the east the Hudson River lowland extends farther to about seven miles from the river, bearing on its back in the Becraft outlier, a remnant of the old Helderberg plateau. A third level, recognizable only in the east is that of the phyllite plateau, rising from 750 feet to 1000 feet and beyond the Harlem valley and the Taconic mountains (see figure 8). It is readily recognized that these plains and plateaus are differ- ential erosion features. This is obvious from the fact that the plain is cut across folded and faulted rocks and that hills of harder rocks, so-called monadnocks, rise above these plains indicating former erosion levels. The Becraft Mountain outlier was mentioned already. It is a relict mountain. Distinct monadnocks are Mt Merino and Church hill south of Hudson, Blue hill south of Greendale and Mt Tom southwest of Blue hill. They rise abruptly 300 to 350 feet above the river plain (see figures 2 and 3). Mt Merino and Blue hill are due to upfolded masses of hard Ordovician Normanskill chert, Church hill and Mt Tom to hard folded beds of Lower Cam- brian Nassau quartzite and Schodack limestone. The phyllite plateau is also a differential erosion plain. It mainly projects through the greater hardness of the slightly metamorphosed Nassau, Schodack and Normanskill beds. The Harlem valley on the other hand has been sunk into the folded mountain masses by the presence of a belt of pure Cambro-Ordovician limestone (Stock- bridge limestone) that is more easily dissolved and eroded than the phyllites adjoining in the west and the hard schists that form the Taconic mountains. It is a question how much these erosion plains partake of the nature of true peneplains. The writer has distinguished in the Capital District (1930) three peneplains, viz., the Albany peneplain, an incipi- ent peneplain of the broad inner lowland extending from the Helder- bergs to the Adirondacks, the Helderberg peneplain and the Catskill peneplain and tentatively referred the Helderberg peneplain to the early Tertiary (Eocene) peneplain of the Appalachians known as the Harrisburg peneplain and the Catskill peneplain to the earlier Cretaceous peneplain known as Kittatinny peneplain. It is possible that these peneplains are much younger than has been supposed and only of middle and later Tertiary age. The Helderberg peneplain rises to 2000 feet southwest of Albany and gradually descends south- 10 NEW YORK STATE MUSEUM ward around the Catskills owing to the southwest dip of the harder Devonian limestone beds which control the weathering. FOSSIL PENEPLAIN A plain that appears to be a most striking fossil peneplain is developed at the base of the Silurian Manlius limestone. It is well seen around the Becraft Mountain outlier. Here north-striking belts of Lower Cambrian Nassau beds and Schodack limestone and Ordo- vician Normanskill chert and shale are seen to disappear successively from east to west under the Silurian-Devonian outlier and to reap- pear in the north from under the outlier. It is therefore obvious that here Silurian beds were spread over an even surface of strongly folded beds of greatly varying ages. West of the Hudson river the Manlius limestone rests on Normanskill grit and shale. This pre- Manlius peneplain stands at Becraft mountain at 200 feet above sea level and it holds the same level in the long contact line from Catskill to the south margin of the quadrangle. It is therefore probable that this contact plain of the Cambro-Ordovician and late Silurian was originally a wide uniform plain of erosion approaching a peneplain. There is, however, also evidence of marine erosion by the invading Manlius sea. A good exposure is that figured by Schuchert and Longwell (’32, p. 319; see also our figure 4) in the Jonesburgh quarries at the northwest side of Becraft mountain. Here Manlius rests with an angular unconformity in broad folds on much crumpled Normanskill shale. At the top of the Ordovician appear small val- leys which are filled with slightly conglomeratic sandstone, indicating a somewhat irregular surface that was leveled by detritus (Rondout) before the deposition of the Manlius limestone. At the north end of Becraft mountain (see figure 48) an irregular two-foot sandstone bed separates the Manlius limestone from the underlying Schodack beds. At other places, as notably west of the river the contact is a sharp line of unconformity. It therefore seems that the advancing sea filled on one hand depressions with sand and on the other leveled the possibly hummocky surface to a large degree. This is especially suggested by the monadnocks (Mt Merino, Blue hill, Church hill, Mt Tom) which rise as much as 350 feet above the pre-Manlius erosion plain and appear by their bounding cliffs, seen especially well on the east side of Mt Merino, and steep slopes as much like early rocky islands as monadnocks of an erosion plain. It is obvious that they were there before Appalachian folding affected the Silurian and Devonian limestones and that they are not due to that orogenic agent. [11] Figure 2 Blue hill, a Normanskill chert monadnock seen from southeast. (E. J. Stein photo, 1935) [12] Figure 3 Mt Merino, a K onnanskill chert monadnock, seen across the Hudson river from northwest. (W. Goldring photo, 1936) GEOLOGY OF THE CATSKILL QUADRANGLE 13 While we thus see that the general setting of the topography of the region and, especially, the carving out of the different levels or erosion plains is controlled by the relative hardness of the rock formations, it is also readily recognized in a study of the topography and geology of the area that two other geomorphologic factors have largely contributed to the minor features of the topography. These are the folding, faulting and the resultant strike of the rocks and the action of the continental glacier. OROGENIC FACTORS OF TOPOGRAPHY The tectonic features of the country rock will be dealt with in another chapter. It may suffice here to state that the north to north- east strike of the Cambrian and Ordovician rocks is the controlling agent of many of the higher hills, as notably Mt Merino, and of an endless number of smaller ledges and ridges of Cambrian Nassau quartzite, Schodack limestone and Ordovician Normanskill chert and grit which partake of the nature of “hogbacks.” As a glance at the map will show, these harder rocks appear everywhere above the glacial deposits where many of them are spaced out from the glacial cover by the overprint. Some are also distinctly influenced by over- thrust planes as notably the long curving ridge extending south from Mt Merino through Church hill to Mt Tom. On account of the infertility of the rocky ledges, these hills are usually wooded or bear pastures in contrast to the drumlins and eskers which are covered by orchards or vineyards. While the smaller ledges, of which there are too many to be shown on the map, and the drumlins regularly strike from north to south, the larger hills, or monadnocks as Mt Merino, Blue hill and also Becraft mountain show a distinct north-northeast strike. It is apparent that the smaller rock outcrops were controlled in their outlines by the ice moving down the valley bottom, while the larger hills and mountains follow the strike of the hard rocks that preserved them as monadnocks. While the multitude of north-south striking ledges of rock, mostly Normanskill grit or Normanskill chert but often also Nassau quart- zite or Schodack limestone, form the wooded hills, the intervening broader fertile valleys are usually underlain by the softer shales of these formations, which were first removed in part by the advancing ice and afterward the depression filled in again with drift or allu- vium. The landscape is therefore characteristically divided by wooded rocky hills, or drumlins with orchards and north-south ex- 14 NEW YORK STATE MUSEUM tending valleys in which the fields and pastures are located. The roads run usually at the foot of the hills, where also the farm houses are located. Such charming and fertile farming country is especially well seen in the region extending south of North Germantown beyond Germantown to Madalin. The left side of the river for half a mile to a mile above the steep riverbank south from Linlithgo to Barrytown and beyond is prac- tically devoid of soil and is now a wooded region, in which the palatial homes of the wealthy New York people are located in parks overlooking the river. The fact that in traversing the area one passes innumerable ledges of Cambrian limestone or quartzite and Normanskill grit or chert gives one the impression that these are the principal country rocks. This is, however, not the case, for the great bulk of the component rocks is shale, mostly barren, greenish gray shale, both in the Cam- brian and in the Ordovician formations, which is, so to say, the matrix in which the others, especially the quartzites, limestones and grits (to a lesser degree the cherts) are carried. These great shale masses are, owing to their softness, buried out of sight in the numer- ous longitudinal depressions between the ridges and exposed only rarely in specially deep valleys, as for instance in the lower stretch of the Roeliff Jansen kill, where 60 feet of dark Normanskill shale without any grit are exposed. Besides the lower Roeliff Jansen valley, some other broader depressions, now filled with glacial debris are obviously also due to the erosion of underlying shales. Such an area is the broad glacial belt of good farm land extending from Cheviot past Madalin to Barrytown and coming out in North and South Bay. This shale belt is flanked on the west by the Normanskill grit belt extending above the river and is continued in Magdalen and Cruger islands, while on the east chert and grit ridges protrude, as well as drumlins that were built above rock ledges. Also the broad valley extending south of Hudson between Mt Merino and the Becraft hills, that is now filled with morainal material and lacks all outcrops, is probably an old large preglacial valley eroded in shale. The principal orogeny that affected these rocks was undoubtedly the pre-Silurian Taconian orogeny which in a general way followed the Precambrian grain of the continent, that is the structure of the fundamental Precambrian complex, along the east coast of North America. Its general strike is to northeast in eastern America; locally on our quadrangle it varies from north to north-northeast. [15] Figure 4 Unconformity at Jonesburgh quarries, west side of Becraft mountain. Valleylike depressions in crumpled Normanskill shale, filled with local Silurian (Rondout beds). View looking east. (From Schuchert and Longwell, 1932) GEOLOGY OF THE CATSKILL QUADRANGLE 17 The Appalachian orogeny is recognizable in the folding and fault- ing of the Siluro-Devonian rocks of the Helderberg plateau west of the river and to a lesser degree also in Becraft mountain which forms a low syncline and has probably survived for that reason as an outlier. The influence of the Appalachian orogeny on the earlier Taconian folding is difficult to establish. It would seem that it was very superficial in this area, as otherwise the Ordovician-Silurian unconformity would be distinctly affected and not form a horizontal plane. GLACIAL FACTORS OF TOPOGRAPHY The glacial factors will be fully dealt with in another chapter by J. H. Cook. We shall therefore only mention here the general features. The obvious, coarser topographic results of glacial action in this area are the erosion, the lack of original soil, the mantle of drift, the drumlins, the kettle hole lakes, the wide alluvial plains now drained by insignificant brooks and the complete alteration of the preglacial drainage as far as the minor water courses are concerned. The erosion is principally recognizable in the numerous rock ledges now striking from north to south more or less with the movement of the last Wisconsin glaciation, which alone is here recognizable. They all expose the fresh rock on top because the original soil-mantle has been carried off. It is interesting to note here, however, that the soil has not been carried away so completely as is generally assumed. This becomes especially conspicuous above and along the ridges of Schodack limestone and ferruginous grit as in the large Cambrian inlier east of Germantown. Here the southern fingers can well be traced by the red to orange-red color of the soil on the ridges, which originates from the underlying Schodack beds, showing that the last drift was merely local to a large extent. This close relation of the deeper glacial drift with the underlying rocks, especially recognizable in the color above Schodack beds, but often also in the black shale debris above Normanskill, had already been noticed on the Saratoga- Schuylerville quadrangles (1914) and in the Capital District (1930). It is possible that it points to the very last stages of the glaciation. The drift mantle of typical moraine is conspicuous in many areas and sometimes, as along the lower Roeliff Jansen kill it reaches the great thickness of a hundred feet or more. It therefore has been most effective in filling former preglacial valleys to the general country level as in the case of that creek. Larger glacial boulders are, on the whole, rare in the area, probably 18 NEW YORK STATE MUSEUM because much of the original drift is covered by later postglacial de- posits. One large boulder of very fossiliferous New Scotland lime- stone, 30 feet long and 15 feet wide, was seen in a pasture, three- quarters of a mile southeast of Livingston and another large block of Nassau phyllite standing upright in the alluvial plain of Roeliff Jansen kill. The latest stages of glaciation produced under the ice the numerous rounded longitudinal hills known as drumlins. They are composed of more or less unstratified material. Some are shown south of the Greendale road, west of the Precambrian inlier. Most distinct and regular drumlins arise in a row from east to west southwest of View- monte (see figure 8). Another double east-west row is seen east of Madalin. The northern row proved especially interesting, as the road leading east from Madalin, in being straightened and macadamized, had been cut into the north ends of these drumlins and there exposed rock cores of Normanskill grit, which obviously had furnished the starting points for the drumlins. Unfortunately the slumping of the overlying material and the building of walls for the protection of the roads have later covered these rock cores again, but the map shows the exposures by the overprint along the road. There is another group around Elizaville and a very peculiar rounded one a mile east of Blue Stores. The opposite of the drumlins are the kettle holes which form a number of charming lakes in the eastern area of the quadrangle (see figures 5 and 6). These are Bell pond, at the northeastern edge of the quadrangle, the Twin ponds north of Elizaville and Warackamac lake near the southern edge. The near-by Spring lakes are bounded by rock on one side but had the same origin. The kettle hole lakes are surrounded by glacial drift, mostly mo- raine, and, quite obviously, mainly due to the filling in of material around iceblocks that remained for a time when the ice finally with- drew and melted away. A most striking feature is the wide alluvial plains which extend between the hill regions as notably southeast of Becraft mountain, west of Livingston, along the Roeliff Jansen kill from Blue Stores south to Elizaville and an especially large area extending north from Elmendorf along the upper reaches of Stony creek to near View- monte. To what extent these fertile, very flat alluvial plains are old bottoms of lakes that were left after the glaciation and have since been drained or were formed by frequent inundations from brooks or damming of brooks is a subject for the specialist. [19] Figure 5 Twin pond in kettle hole near Elizaville. (E. T. Stein photo, 1936) [20] Figure 6 YVarackamac lake near Cokertown, a typical kettle hole in glacial drift. (E. T. Stein photo, 1936) GEOLOGY OF THE CATSKILL QUADRANGLE 21 Some of these alluvial plains, as that of Stony creek, mentioned above, that are not entirely level, but are slightly graded downward, were probably gradually built up along the creeks by successions of beaver dams. The early settlers called many of these places “beaver meadows,” being well aware of their origin. Most of these alluvial plains are usually considered as old late glacial lake bottoms. It is obvious that these rich bottom lands were the earliest to be chosen by the mostly Dutch settlers that spread northward through the Hudson valley and some families became prominent in early days by their rich lands, as the Livingstons on the alluvial plains near the present village of Livingston. The richest orchard and fruit-raising district of New York extends north and south of Hudson over these alluvial bottoms and the deep morainal soil. A most interesting group of deposits of the latest glacial stage are the varved clays covering the bordering lowlands of the river up to about 200 feet and forming in some localities as around North and South bays near the southern edge of the steep grit, banks reaching 140 feet above the river. They extend away from the river to various distances. These clays, which distinctly show the varved structure that is a regular alternation of lighter and darker layers deposited respectively in winter and summer, are by these varves recognized to have been deposited in quiet fresh water. They were formerly sup- posed to have been deposited in one extensive body of water, Lake Albany, extending on both sides of the present river from the region of Kingston to the neighborhood of Saratoga and Schenectady (Woodworth, 1905). More recently there has been brought forward (Cook, 1930) evidence that suggests that instead of one lake there was a series of bodies of water at slightly different levels along the river held in place by residual ice tongues in the river valley. While the coarser features of the topography have resulted from the general erosion of the country that is controlled principally by the rock structure, the finer and final details of the land sculpture have been worked out, according to the studies of John H. Cook, by the stagnant ice at the end of the glacial period. This fascinating chapter of the physiography of the region will be fully dealt with in a separate chapter by Professor Cook. DRAINAGE The present drainage is the last conspicuous and also the most com- plex result of the glacial period. It is well known that the enor- mously thick body of moving ice with its great eroding, transporting 22 NEW YORK STATE MUSEUM and crushing power everywhere completely altered the preglacial drainage by filling in valleys in one place, eroding deeply in softer rocks in other places, thus creating channels for later rivers and lakes. The glacialists are still busy all over northern North America trying to trace the preglacial drainage and many a great river of today is found to be nothirlg but a composite of former and very different drainages. Such a river is the Ohio. The Hudson river existed long before the glacial period. It is even known to have extended 90 or more miles beyond New York at the present bottom of the ocean and to have had already excavated a tremendous canyon through the Highlands and far above to the Albany district before glacial time, facts which indicate a much greater elevation and farther extension of the eastern coastal section of the continent. The history of this fine scenic and historic river is probably very long, going back to the time when this section of the continent last emerged from the sea ; that is, towards the end of the Paleozoic period. Considering the enormous amount of erosion that has been accomplished by the river in digging its bed to present sea level through the 4000 feet of sandstones and shales that now build up the mural front of the Catskill mountains and once extended across the valley to the Rensselaer grit formation, and that it sunk even way beyond present sea level in a deep canyon that has been found below the river channel, it is seen that the history of the river must be enor- mously old. This gorge extends hundreds of feet down (more than 500 feet in the Highlands and about 300 feet at the site of the Pough- keepsie bridge) and was formed when this part of the continent stood thousands of feet higher than now. The near-vertical rock walls of the present stream bed are therefore only the upper lips of the old gorge, which according to Cook is not very deep through the Catskill quadrangle. Where these walls are broken down as at the North and South bays and varve clay forms the riverbanks, preglacial tributaries must have reached the stream. There is little doubt that the Hudson river carried out this ero- sional work in Mesozoic and Tertiary time beginning its course on top of the beds that now compose the Catskills and possibly even higher on beds of Carboniferous age that must have extended northward from Pennsylvania. The stages by which this great river was de- veloped are still clothed in mystery as is evidenced by the fact that widely opposing views are held by different writers. While Davis (1892), the pioneer in this field, held that the Potomac, Susquehanna, GEOLOGY OF THE CATSKILL QUADRANGLE 23 Delaware and Hudson are now abnormal in flowing from the Alle- gheny plateau (and Adirondacks) across the inner lowland and out through the oldland to the Atlantic, Johnson (1931) has thought to account for this abnormality by the ingenious hypothesis of an exten- sive coastal plain cover, extending 125-200 miles back into the country on a very ancient peneplain of pre-Schooley (or pre-Kittatinny) age, from which the rivers were let down in their present courses on the buried irregular topography of mountain folds, and held their original consequent courses. The writer (1932) on the other hand has tried to explain the drain- age of the Susquehanna, Delaware and Hudson rivers in the Catskill and surrounding nearer regions by assuming that the Susquehanna (see figure 7) was the original consequent river flowing southwest with the dip of the general surface towards the sea and that later the Delaware and Hudson took advantage of their shorter courses and steeper gradients to behead the upper branches of the Susque- 24 NEW YORK STATE MUSEUM hanna in the east and develop straight north-south courses largely by piracy, at least in their upper reaches as indicated by the diagrams. Recently Meyerhoff and Olmsted (1936) have advanced the view that the original trunk rivers were headed southeast in conformance with the southeast dip slopes of overthrust folds, thrust sheets and Paleozoic formations that have been removed. These streams are in- ferred to have been flowing in Triassic and early Upper Cretaceous times and to have been altered later by the irregularities of topog- raphy induced by the differential hardness and structure of the under- lying formations. There is no doubt that the Hudson river has held its preglacial course through the various glacial and interglacial periods, and that it thus reaches back at least to Cretaceous times or, taking the end of the Mesozoic era as a measure, some 73-75 million years according to Holmes and Lawson’s lead-ratios in the calculation of ages of radio-active minerals (1927). If we now turn to the tributaries of the Hudson river on the Cats- kill quadrangle, (see figure 8) we find on the west side the Catskill and the Esopus creeks which both have their entire courses in the Devonian rocks, mostly of the Catskill mountains and only their mouths in the Ordovician. They, therefore, lie outside of our field of investigation. On the east side there are also only two creeks of notable size, the Taghkanic creek which in the northeast corner flows into the smaller Claverack, the latter continuing its name until it reaches the Kinderhook creek north of our quadrangle. The most notable creek is the Roeliff Jansen kill which derives its name from an early Dutch settler. Arising in the Harlem valley at the foot of the Taconic Mountain range in a latitude to the north of the upper margin of our quadrangle, it flows south in the Harlem valley for about two-thirds of the quadrangle, swings to the southwest into the phyllite plateau turning sharply northwest just beyond the southeast corner of the Catskill quadrangle to pursue a northwest course to the edge of the phyllite plateau and then flows north-northwest to the Hudson. The creek has thus a most remarkable angular course with a reversal in the second half (see figure 8). A glance at the map shows that the Taghkanic follows an exactly parallel course, also with a reversal in the phyllite plateau. And the Kinderhook creek to the north of our quadrangle also has a somewhat similar course in arising behind the Rensselaer grit plateau and breaking through the phyllite plateau in a curve. It, however, swings then to the southwest. The courses of these creeks, especially the retrograde parts, indicate GEOLOGY OF THE CATSKILL QUADRANGLE 25 26 NEW YORK STATE MUSEUM that they have a very complex history, and Professor Cook holds that they are composites made up from sections of various preglacial rivers. There as yet are not sufficient data at hand to elucidate their history, but Professor Cook will present some provisional conclusions. It is a remarkable fact that the Roeliff Janseh kill sinks in its lowest course into a 100-feet deep drift mantle, reaching Normanskill shale and grit bedrock at the bottom. It obviously has discovered there an old preglacial river course, but it reaches this by breaking through a grit ridge west of Blue Stores*. Stony creek drains a wide alluvial plain east of Madalin and leaving this breaks also through a prominent grit ridge and reaches the Hudson river at a steep grade. ANCIENT BEAVER MEADOWS Alluvial plains of the type of the fertile Stony Creek plain east of Madalin have currently been considered as old postglacial lake bottoms. More recently (Ruedemann and Schoonmaker, 1938) the fact has been recognized that these level valleys, which show a gentle grade downstream and are strikingly horizontal from bank to bank owe their configuration to the activity of beavers, who by building dams in the valleys for thousands of years in postglacial time gave the valley bottoms an even grade down the valley and a horizontal surface from one side to the other. The Stony Creek alluvial plain is one of the most striking examples of a valley formed from ancient “beaver-meadows” by the aggrading activity of beavers. This alluvial plain evenly declines from 216 feet A. T. at the upper end to 164 feet at the outlet. The Sawyers Kill alluvial plain running northward from Saugerties is another distinct example of aggrada- tion by beavers. RELATIONS OF GEOLOGY AND TOPOGRAPHY TO FLORA, FAUNA AND HUMAN CULTURE OF REGION The great charm of the section of the Catskill quadrangle east of the river arises from the great diversity of the physiographic features, from the multitude of north-south stretching mountains, hills and narrow ridges or single ledges, which are densely wooded or as in the case of the drumlins bear orchards and vineyards, while between extend fertile valleys, nearly all with brooks flowing length- wise in the valleys. Here and there the valleys expand to larger * Probably a simple diversion for this short stretch. The valley seems to have run northwest from Blue Stores (Cook). GEOLOGY OF THE CATSKILL QUADRANGLE 27 alluvial plains which are prosperous farming regions. The region altogether gives the impression of a fertile, yet not monotonous country. The flora has of course been largely restricted to the ridges and gorges, but owing to the great diversity of underlying rocks it ex- hibits considerable variety. According to Bray (’30, p. 69) the Hudson Valley region belongs to the much favored zone B of the vegetation zones of New York, only Staten Island and southern Long Island which belong to zone A having a longer growing period and more favored climate. Zone B which extends up the Hudson valley and through the Mohawk valley to the Lake Ontario-Erie belt and is also found in the Delaware, Susquehanna and Allegheny drainage valleys, is characterized by the dominance of oaks, hickories, chestnut, tulip trees etc. in the woods. Its indicator species are red cedar {Juniper us virginiana) , black walnut ( Juglans nigra), butternut ( Jugians cinerea), the hickories, bitternut or swamp hickory ( Hicoria cordiformis) , shag-bark (H. laciniosa), white-heart hickory {H. alba), small fruited hickory (H. microcarpa) , pignut hickory (H. glabra)', numerous oaks, viz., red oak ( Quercus rubra), swamp or pin oak (Q. palustris) , scarlet oak (Q. coccinea), gray oak (Q. borealis), black oak (Q. velutina), white oak (Q. alba), post or iron oak {Q. stellata), mossy-cup or burr oak (Q. macrocarpa) , swamp white oak (Q. bicolor), rock chestnut oak {Q. prinus) , chestnut oak or yellow oak (Q. muhlen- bergii) ; further the sweet birch {Betula lenta), the chestnut ( Cas - tanea dentata), the hackberry ( Celtis occidentals) , red mulberry (Morus rubra), cucumber tree or mountain magnolia {Magnolia acuminata) , the tulip-tree or yellow poplar {Liriodendron tulipifera), the paw paw {Asimina triloba), the sassafras {Sassafras sassafras), the wild hydrangea {Hydrangea arborescens) , the American crab- apple {Malus ( Pyrus ) coronaria), the sycamore {Platanus occiden- tals), the red-bud {Cercis canadensis), the Kentucky coffee tree ( Gymnocladus dioica), the honey locust ( Gleditsia triacanthos) , the prickly ash {Xanthoxylum americanum) , the flowering dogwood ( Cynoxylon {Cornus) floridum), tupelo {Nyssa sylvatica), great laurel {Rhododendron maximum), mountain laurel {Kalmia lati- folia) . This list of the characteristic trees and bushes of zone B is a won- derful array of beautiful plants which depict a rich tree flora hardly duplicated in any other country of equal temperate climate and most certainly not in Europe with its small tree flora, because it became 28 NEW YORK STATE MUSEUM woefully depauperated by the glacial period which extinguished the multitude of trees that could not withstand the cold and could not escape over the latitudinal mountain ranges of the Pyrenees, Alps, Carpathians and Caucasus. How many of these magnificent trees and bushes as the red oak, black walnut, tulip tree, the honey locust, the great laurel or the mountain laurel, however, does one still see in the woods of the Hudson valley? Man has done there his nefarious work of destruction of wild life only too well. The small herbaceous plants show a similarity in richness. Of these Bray cites the following as indicator species : white dogtooth violet ( Erythronium albidum), lizards tail ( Saururus cernuus), American lotus or water chinquapin ( Nelumbo lutea), golden seal ( Hydrastis canadensis) , wild sensitive plant ( Chamaecrista ( Cassia ) nictitans), partridge pea ( Ch . fasciculata) , shooting-star ( Dode - cathion meadia) , Virginia cowslip or blue bells ( Mertensia virginica) . Several areas in the quadrangle are botanically of greater interest because of their geologic structure and the divergent character of the rocks which lead to particular florulas. Dr Rogers McVaugh of the U. S. Department of Agriculture, Washington, D. C., who for several years has made a special study of the botanical ecology of the Hudson valley, has kindly written the following note on the flora of the principal mountains (and the Hudson estuary) : These hills are covered with a growth of trees, including mostly oaks ( Quercus spp.) and sugar maple ( Acer saccharum) , with dense stands of juniper ( Juniperus virginiana ) covering considerable areas, especially on Becraft mountain. As the stony nature of the soil, combined with the steepness of the terrain, has made agricul- ture, in the main, impossible, many of the steep shaly hillsides sup- port a characteristic and interesting vegetation, which is not to be found elsewhere in the vicinity, and which includes numerous species more abundant southward. Among the junipers and chestnut oaks ( Q . prinus ) are found numerous individuals of the dwarf chestnut oak (Q. prinoides ) and the scrub oak ( Q . ilicifolia ), while the hackberry ( Celtis occiden- tals), is found in abundance. On the dry open hillsides in the spring one finds the bright yellow flowers of the early buttercup ( Ranunculus fascicularis) , and in the more calcareous places the purple virgin’s-bower ( Clematis verticillaris) . Later in the season the visitor finds the showy purple penstemon (P. hirsutus) and on Mt Merino the well-known colony of the prickly pear ( Opuntia vulgaris), which was reported at least as early as 1825 and repre- sents the most northerly known station for this species in the Hud- son valley. Late summer brings out on Blue hill and Mt Merino the brilliant deep yellow flowers of the rare goldenrod ( Solidago GEOLOGY OF THE CATSKILL QUADRANGLE 29 rigida ) as well as the white ones of the milkweed ( Asclepias verti- cillata ). The crimson stamens of the tall grama grass ( Bouteloua curtipendula) also attract the eye, while the botanist might find the interesting but rather less conspicuous false pennyroyal (Isanthus brae hiatus) , the small mosslike plants of the rock selaginella (>S\ rupestris ) and the green milkweed ( Acerates viridiflora) . On the exposed shale ledges of these hills grows the rusty woodsia ( Woodsia ilvensis), while on the limestones of Becraft mountain and Mt Merino are to be found other ferns, including the purple cliff brake ( Pellaea atro purpurea) , the wall-rue spleenwort ( Asplenwm rutamuraria) and occasional patches of the walking fern ( Campto - sorus rhizophyllus) . While the surrounding country has been almost completely altered, since the coming of the white man, by the operations of agriculture, the steep rocky sides of these hills, undisturbed except for occasional cutters of firewood, probably give us a fairly good picture of the original conditions prevailing on them. The rocky gorges, cut into the hard shales of the Hudson valley by small streams entering the river, often afford suitable living con- ditions for plants which are rarely found in this region except at higher altitudes. Examples of such gorges are to be found south of Tivoli, at Cheviot, at Greendale and other points, including the larger one formed by the Roeliff Jansen kill. The most conspicuous plants found in these situations are the white birch ( Betula papyrifera) , the striped maple ( Acer pennsylvanicum) and the mountain maple ( A . spicatum), the leatherwood (Dire a palustris), the stiff gentian ( Gentiana quinquefolia) , the fly honeysuckle ( Lonicera canadensis) and the yellow touch-me-not ( Impatiens pallida). The dry shale bluffs and banks along the river also support a char- acteristic vegetation. Here the traveler finds the arbor vitae (Thuja occidentalis) in abundance; it is found also in the tidal swamps of Rogers island. Along with the arbor vitae grows the often-cultivated ninebark (Physocarpus opulifolius) , the bladdernut (Staphylea tri- folia) and several interesting herbaceous plants, including the so- called yellow pimpernel (Taenidia integerrima) and another golden- rod (Solidago squarrosa) whose large showy flowering spikes make it very noticeable. Of special interest in Doctor McVaugh’s account appear to us those plants which are of southern habitat and reach in the relatively warm Hudson valley their farthest northern station. The most inter- esting of these in the Catskill area are the green milkweed (Acerates viridiflora) which grows on the slopes of Blue hill and the prickly pear (Opuntia vulgaris) which is found on top of Mt Merino, on Church hill and in the woods at the eastern foot of Mt Merino in a few prosperous colonies (see figure 9). It is usually found on outcrops of chert or Normanskill grit, which seem to supply the dry and easily heated soil the plant requires. The pretty patch here 30 NEW YORK STATE MUSEUM reproduced was found surrounded by dense and moist woodland on a little knoll of Normanskill grit. This is the northernmost occur- rence in New York State. On the west side of the river the cactus is also seen on Esopus grit northwest of the West Shore Railroad station (fide Chadwick) at Saugerties. Also the juniper ( J uni perils virginiana) , popularly known as red cedar, prefers ridges of chert or grit and it grows in great numbers where pastures on these rocks are returning to woodland, as shown in figures 10 and 11. The fauna, according to information given me by W. J. Schoon- maker, assistant state zoologist, is strongly divided between that of the wooded lands of the phyllite plateau and Taconic mountains and the open cultivated plains to the west of them. The little settled woodlands along the southeastern edge of the quadrangle and beyond and especially the Taconic mountains are inhabited by deer and wild cats, red and gray foxes, red and gray squirrels, the pine mouse, the short-tailed shrew, smoky shrew and the masked shrew, Brewers mole, the star-nosed mole and the inter- esting flying squirrels. Muskrat, mink and raccoon are found along waterways and in wooded swamps of the region. Beavers have been extinct for a long time in this region but they have left physiographic records in the “beaver-meadows,” alluvial plains now extending along some of the creeks (see page 26). Both in the woods and cleared lands occur the cottontail rabbit, the skunk, the small brown weasel and the New York weasel. Ruffed grouse are common in the woods and pheasants in the open land, while along the Hudson river one may see, during migration, thou- sands of wild ducks. Wild black ducks live and breed in great numbers along the river, where the wild rice of the river swamps supplies them with plentiful food. Rattlesnakes and copperheads or moccasins occur on the rocky ledges of the less settled areas. I have seen water snakes repeatedly in the Roeliff Jansen kill as well as black snakes, and one day I saw a small flock of egrets in one of the wild rice swamps. The river valley was settled early as the river formed the most important highway from New York to the interior for more than two hundred years, and as Brigham (1928) has emphasized it formed together with its extension through the Champlain valley northward to Montreal the most strategic and important road of the early his- tory, especially in the Revolutionary War, which until the battle of [31] Figure 9 Northernmost station of prickley pear ( Opuntia vulgaris) in Hudson valley. The plant grows on small outcrop of chert which provides a warm, dry soil surface. Eastern foot of Mt Merino. (J. W. Graham photo, 1935) [33] Figure 10 Ledge of white-weathering Nornianskill chert (white areas) east of Blue hill, showing growth of red cedar ( Juniherus virciiniana) . (W. Goldring photo, 1936) [34] Figure 11 Young forest of red cedar appearing upon Normanskill chert plateau, east of Blue hill. (W. Goldring photo, 1936) GEOLOGY OF THE CATS KILL QUADRANGLE 35 Saratoga, turned for a long time about the possession of this stra- tegic road. Owing to this strategic position early flourishing settlements grew along the river, the most important of which on our map are Hudson on the east side and Saugerties and Catskill on the west side. Hud- son is located on a bluff of Normanskill chert jutting out into the river between two (former) bays, and Catskill and Saugerties are located at the mouths of large creeks (Catskill and Esopus respec- tively) which furnished both water power and convenient harbor facilities. As the river is an estuary large ships could reach these ports in early times and it is known that several prominent pirate captains had their headquarters in Hudson in the old days; even Captain Kidd is believed to have lived there sometime and buried his treasure somewhere near the river. It is thus seen that romance and history are not foreign to these shores, from which the section that harbored Rip Van Winkle can be clearly seen. Also some of the villages, as Germantown which was founded by the palatinates, have a long history. The river is still a highway of traffic both on water where ply the largest and most luxurious river steamers of the world and along its banks, where close along the east shore the New York Central Railroad, one of the principal systems of the country, sends its fast passenger trains and huge freight trains over four tracks and on the other side of the river the West Shore Railroad supplies another out- let for the enormous freight being shipped to and from New York. The opening of the port of Albany at the head of navigation has even brought ocean steamers into the river and one may now see the flags of foreign countries flying over the placid waters of this great estuary. We have already mentioned the prosperous farming population that inhabits both the east and west sides of the river lowland, as far as the phyllite plateau which has today even fewer inhabitants than it had in olden days and has mostly returned to woodland. The rich land of the glacially filled valleys is given up to fruit farming (trees and berry bushes) on a large scale, the rich alluvial land to dairy farming. This industry is greatly helped by the nearness of the great market of New York and the excellent transportation facilities both on water and land. The presence of Devonian limestone that is suitable for the manu- facture of Portland cement in Becraft mountain and in the Helder- 36 NEW YORK STATE MUSEUM berg plateau on the west has provided the material for the most im- portant eastern New York cement industry that is flourishing at Hudson, Alsen and Malden and that, as well as the brick manufac- ture in the valley which is dependent on the Albany clay, is greatly aided by the cheap river transportation to distant ports. The river, freezing over in the winter, formerly supplied New York City with ice and the riverbanks were lined with unsightly icehouses. This industry has vanished owing to the unsanitary con- dition of the water. A few of the icehouses have remained and been readily adapted to a new industry for the region, that of mushroom raising. A very clear view of the exceptional natural advantages of the Hudson Valley region in general and the sector of it in the Catskill quadrangle here under discussion is obtained by a perusal of the report of the New York State Planning Board, submitted to the Governor and transmitted to the Legislature in January 1935. It is there seen from the charts that submarginal farm and idle lands are found only on the phyllite plateau and are entirely absent in the Hudson Valley lowland ; that the latter is located in the most favored “valley belt” of the State which extends up the Hudson river and west through the Mohawk valley and the Lake Ontario plain and contains six of the seven great metropolitan centers of the State and, though containing only 16 per cent of the land area, includes 84 per cent of the population ; that it lacks larger areas of excessive slope, unfit for farming, the only exceptions being the large monad- nocks ; that in soil productivity it ranks medium to high ; that the U. S. Soil Erosion service found only slight sheet erosion with occa- sional gullies (in clay beds) in the western part and moderate sheet erosion without gullies in the eastern part ; that the population density is high (in spite of the prevalent farming), being 30 to 50 a square mile in the eastern part and over 50 in the western part near the river. Corresponding to these facts also the value of real prop- erty a square mile moves in the highest brackets in the area, 50 to 100 thousand dollars and over 100,000 closer to the river, while, cor- respondingly the percentage of State aid of total town revenues is very low, 0 to 25 per cent, in the western part near the river and 26 to 50 per cent farther east. In spite of these advantages and the closeness of the metropolitan markets of New York and Albany the agricultural population has shown a slight decrease from 1900-30 in the area as in all agricultural regions except close to the metropolises. GEOLOGY OF THE CATSKILL QUADRANGLE 37 DESCRIPTIVE GEOLOGY The Cambro-Ordovician belt of the Catskill quadrangle contains formations of the Lower Cambrian (Taconian), Canadian and Ordovician systems. All of these were deposited in the eastern or Levis trough of the Appalachian geosyncline while the formations that belong to the western or Chazy trough series and are known from the western Saratoga and Capital Districts are buried under the Catskill mountains, but reappear in New Jersey and Pennsylvania. CAMBRIAN SYSTEM The mapping on the Catskill quadrangle has brought out a much wider distribution of Lower Cambrian (Taconian) rocks than was expected. The latest State Geological Map (Merrill, 1901), ends the Lower Cambrian belt of northeastern New York at Stockport, north of Hudson and shows from the latitude of Hudson to the southern edge of the quadrangle only ‘‘Hudson river” and “Hudson river metamorphosed” to the limestone belt of the Harlem valley, with the exception of a very narrow short strip south of Elizaville. Nor do later maps, as in plate I of the 16th International Geological Congress guidebook 1, show any indications of the presence of large areas of Cambrian rocks. As in the Capital District the older Lower Cambrian rocks (the Nassau beds) are again distributed in the east, the younger ones in the west. Walcott (1888, plate 3), on the other hand, referred on his map the entire belt as far as the eastern limestones, except a very narrow strip along the river, to the Cambrian, extending this Cambrian belt to the northern boundary of Columbia county. The present map shows a wide distribution of Lower Cambrian rocks also south of Hudson and we have observed on occasional field trips that the Lower Cambrian rocks extend southward through the slate belt to the Highlands and into the valley behind them and east- ward into the metamorphosed belt along the Massachusetts line. In the Capital District (1930, p. 25) we have distinguished in the Lower Cambrian the following formations (oldest at top) : 1 Nassau beds 2 Bomoseen grit 3 Diamond rock quartzite 4 Troy shales and limestones 5 Schodack shales and limestones Of these only the Nassau beds and Schodack shales and lime- stones are well developed on the Catskill quadrangle as mapable 38 NEW YORK STATE MUSEUM formations and the Bomoseen grit is present as a narrow, more or less transitional horizon and the Troy shale is not well enough dis- tinguishable from the Schodack shale and limestone to be mapped separately. The Diamond rock quartzite has not been noticed. To these must be added the Zion Hill quartzite Ruedemann (Fer- ruginous quartzite Dale) which though not noticed in the Capital District, is, if a thin, at least a distinct member of the Lower Cam- brian south of Hudson. Nassau Beds The Nassau beds (Ruedemann, 1914) were first distinguished by Dale (1904, p. 29) as the beds A-E of his Lower Cambrian series as exposed in Rensselaer county and part of Columbia county. These beds were in ascending order : Description of strata Fauna Thickness estimated in feet E Greenish, or reddish and greenish Casts of impressions 65-535 D shale with small quartzite or grit beds. Massive, greenish quartzite, in places very coarse. 10-50 C Reddish and greenish shale with Casts of impressions, 30-80 B small beds of quartzite or grit (rarely up to five feet thick). Massive greenish quartzite, in places very coarse. Oldhamia 8-40 A Reddish and greenish shale with Casts of impressions, 50-80 small beds of quartzite or grit, from 1-12, and rarely, 24 inches thick. Oldhamia Most of these divisions are recognizable in the Catskill quadrangle in southern Columbia county, although mostly so involved by folding as to be difficult of separation. The largest division E composed of an endless repetition of greenish gray shales with thin greenish quart- zite bands (from an inch to half a foot) is best exposed in the phyl- lite plateau in the southeast corner of the map, where the rock is slightly metamorphosed into phyllite. Figures 12 and 13 well il- lustrate this alternation as exhibited in a new road cut near Jacksons Corners (just beyond the southeast corner of the quadrangle). [39] Figure 13 Further enlargement showing alternating phyllite and quartzite hands. (T. W. Graham photo, 1935) [40] GEOLOGY OF THE CATSKILL QUADRANGLE 41 A continuous fine series of outcrops of Nassau beds is exposed along the new road from Eiizaville to Jacksons Corners along the Roeliff Jansen kill (see figures 56-59). No section is obtainable there, however, as the same beds are repeated in a series of three fiat anti- clines (see below p. 145). Thicknesses of 40 feet and more of the alternating greenish gray shale and thin greenish quartzite beds were observed southeast of Becraft mountain and in the Roeliff Jansen kill. Dale’s divisions B and D of massive greenish quartzite, in places very coarse, which are well exposed in the Capital District, were not ob- served on the Catskill quadrangle ; they are, however, present directly north on the Coxsackie quadrangle. Also black shale occurs with the thin quartzite near Eiizaville. Dale (’99, p. 178) has estimated the maximum thickness of the Lower Cambrian at two places (Mt Hebron and east of North Gran- ville) and obtained a maximum figure of 1400 feet, which, however, is probably exceeded, as the base of the Nassau beds is not known. Of these 1400 feet the Nassau beds with a maximum of 785 feet occupy the major portion. Dale adds in a footnote that a recent measurement of the Lower Cambrian quartzite on the Green Moun- tain range opposite Bennington exceeds 1500 feet. It is therefore apparent that the thickness of the Lower Cambrian amounts to 2000 feet or more. Only a small portion of the Nassau formation is ap- parently exposed on the Catskill quadrangle, namely the uppermost division E, but it is often repeated in folding. An elaborate description of the petrographic character of the Nas- sau beds has been given by Dale (1904, p. 16-17). “The greenish shale, occasionally slightly reddish or blackish” is described as being under the microscope “a very fine-grained aggre- gate of muscovite and chlorite scales, angular quartz grains, rarely pla- gioclase grains, with brownish dots which are probably limonite.” It is added that “the microscopical composition and structure of this shale indicate that it would probably not have required a vastly in- creased amount of compression to transform it into schist.” Regarding “the greenish coarse and fine quartzite beds” inter- bedded with the red and green shale bearing Oldhamia occidens, it is stated that these differ little from the other quartzites of the Lower Cambrian beds “except in the occasional abundance of chlorite or chlorite schist areas or fragments.” “The reddish shale associated with all these quartzite beds varies much in the amount of its hematite and, therefore, the intensity of its color.” “The green shales owe their color to chlorite, the purplish 42 NEW YORK STATE MUSEUM ones probably to chlorite and hematite, and the blackish ones, naturally, to carbon.” It is a remarkable fact that the great mass of Nassau beds has never afforded any fossils save the Oldhamia impressions. This ab- sence of preservable organic life is to some extent in favor of the view that this formation may be a very late Precambrian or a tran- sitional one from the Precambrian to the Cambrian (see below p. 58). Oldhamia occidens Walcott, was described originally as a calcare- ous alga from the beds of the Troy quadrangle (Walcott, 1894). Later the organic nature of Oldhamia was denied by Roemer (’80, p. 130), Sollas (’86) and the paleobotanists Solms-Laubach (1891), Seward (1898), Potonie and Gothan (1921), but its algal nature re- affirmed by Ruedemann (1929). Recent collections of fine material of Oldhamia occidens in the eastern slate belt of New York and a restudy of the British types of Oldhamia radiata and antiqua have led to the discovery that all these remarkable impressions, both in the shale and in the quartzite, are radiating feeding trails of worms such as have been fully described by Richter both of recent and of fossil occurrence. The writer has given a fully illustrated account of these interesting fossils in Bulletin No. 281, of the New York State Museum (1929). As Oldhamia occidens is thus found to be an actual fossil and occurs only in the Nassau beds, it is a good index fossil of these beds. Note. The Nassau beds were placed by an unfortunate slip in the printing of the table of formations in the Capital District (1930, p. 27) in the middle of the Lower Cambrian, instead of at the base, although distinctly considered in the text as belonging there. This error has crept also into Miss Wilmarth’s elaborate correlation table of the New York formations (northeastern New York column). Bomoseen Grit This name was proposed by Ruedemann (T4, p. 69) for Dale’s “olive grit (division F).” It is defined by Dale as “olive grit, meta- morphic, usually weathering reddish; absent at south.” It is given in Rensselaer county a thickness of 18 to 50 feet. It is a very prom- inent member of the Lower Cambrian series in southern Vermont and Washington county of New York and there reaches a thickness of 200 feet. The writer found it strll a striking formation along the eastern edge of the Schuylerville quadrangle and it is also well shown in the Capital District where a belt passes through the eastern portion of and back of the city of Troy and east of Lansingburg, the belt striking over to the northeast towards Raymertown. In all this area GEOLOGY OF THE CATSKILL QUADRANGLE 43 the ledges of either fresh olive-green or weathered pale brick-red rock are easily observed from the road. This is not the case farther south. Directly south of the Capital District, on the Coxsackie quadrangle, it is still recognizable as a transitional band between the Nassau and Schodack beds, and it ap- pears also as such between the Nassau and Schodack beds on the Catskill quadrangle, in the west at the southeast corner of Mt Tom as a distinct narrow belt, and again at the south end of a small inlier of Lower Cambrian rocks, a mile east of Mt Tom and finally also in a road cut south of Bell pond and on top of a ridge west of it. In all these localities it outcrops close to the Schodack thin-bedded and brecciated limestones, ferruginous quartzite etc. All these occur- rences are repetitions of the same beds in an east-west succession produced by folding. The full thickness of the Bomoseen beds or olive grit has not been obtained, but it is apparently not more than 20 feet. South of Elizaville we found 10 feet exposed, 15 feet below ferruginous quartzite and resting on thin-bedded quartzite. A careful petrographic description of this peculiar rock has been given by Dale (1899, p. 179) from which we quote: A greenish, usually olive-colored, very rarely purplish, more or less massive grit, generally somewhat calcareous and almost always spangled with very minute scales of hematite or graphite. Under the microscope it is seen to consist mainly of more or less angular grains of quartzite, with a considerable number of plagioclase grains, rarely one of microcline, in a cement of sericite with coarse calcite and small areas of secondary quartz. . . .The scales of hematite, sometimes graphite, can be made out with a magnifying lens. We are especially interested in this brick-red-weathering rock, because it carries a steady, though small iron content (hematite) and because it holds the horizon of the iron beds in Columbia county between the Nassau and Schodack formations (see below). Fossils are extremely rare in the Bomoseen grit and we have made no special efforts to collect any. Walcott (T2, p. 188) has reported specimens of Obolella crassa from the formation. We have mapped the narrow strips of Bomoseen grit with the Schodack formation into which the grit appears to grade and of which it may be a local facies or basal member. Burden Iron Ore We will designate here as the Burden iron ore a formation that is found as limonite and siderite iron ore between the Nassau and Schodack beds in a belt extending from the southern base of Mt 44 NEW YORK STATE MUSEUM Tom (Mt Thomas) to Church hill, about four miles in all. Here ore was mined until 1901 in the Burden mines at Mt Tom and in other mines in Plass hill (now Church hill). Altogether four separate “basins” were distinguished by Kimball (1890, p. 157), separated by barren rock (see chart, figure 14). Kimball constructed a series of sections (see chart), in which he considered the iron ore beds as the eastern limbs of anticlines that are continued eastward as small syn- clines and anticlines. We shall see that the regular easterly dip of the ore beds is not so much the result of folded, as of overthrust structure, the ore bed being overthrust with the rest of the Lower Cambrian on Normanskill grit. Nor are there separate basins of GEOLOGY OF THE CATSKILL QUADRANGLE 45 iron ore for it is a continuous horizon, that is folded and faulted out in the intervening stretches. The iron-stained deep red rock and soil is continuous on top of the ridge from Mt Tom to Church hill, where the old Plass Hill mines were. A very instructive sec- tion across this ridge, where before it showed very little indica- tion of iron ore, has been made by the new road cut (see figure 18) on the road from Greendale Station to Greendale. Here on the south side of the road, an ore bed 18 feet six inches thick, resting directly on Nassau quartzite and shale is well exposed, while directly across on the north side this ore bed is again faulted out and only the red-stained adjoining rocks and a crush zone are exposed. It is obvious in this section that much slipping and faulting has disturbed the relative original thicknesses of the beds ; one fault passing through the overlying Schodack limestones and another separating the Scho- dack and overlying Deepkill beds, with a small wedge of ferru- ginous quartzite caught in the fault. Kimball’s chart of the iron basins (see figure 14) also shows various transversal faults which offset the outlines of the basins, especially strongly so at the Plass Hill mine and his longitudinal sections BC and JK show distinctly the interruption of the basins by folding and faulting, South basin being separated from Second (Burden) basin by an eroded anticline. The typical outcrop of the Burden iron ore is at the old adit of the Burden mine. Here the following section was found (see plate and text figure) in descending order: 1 20 feet brownish-weathering, very heavy quartzitic limestone. 2 5 feet shaly, thin quartzite. 3 13 feet heavy-bedded gray quartzitic limestone. 4 6 feet thin-bedded quartzitic limestone. 5 25 feet iron ore, conglomerate with calcareous matrix, full of rounded quartz-grains. 6 Shale with thin quartzite beds. Nassau, forming base of sec- tion. At the Church Hill iron mine, which is now filled in, the writer found, when he first came there, in descending order: 1 10 feet limestone full of rounded sand grains. 2 2 feet limestone. 3 \y2 feet thin-bedded quartzite. 4 7 feet iron ore exposed. Foot wall not exposed. 46 NEW YORK STATE MUSEUM The iron ore beds in both the Church Hill and the Burden mines contain layers of limestone breccia, in the Church Hill beds appar- ently of the nature of a crush breccia. The Nassau shale and quartzite is exposed on the slope of the hill directly below the mine adit (see figure 15), at the western brow of the hill. A most significant observation made at the time of the first inspection of the mine was that of the presence of slabs, a foot in diameter, of greenish Nassau quartzite in the iron ore bed which was a breccia with limestone pebbles. This left little doubt that the Burden iron ore bed rested directly on the Nassau, probably with a discon- formity. Age of Burden iron ore. The exact age of the iron ore was not known to the earlier writers. The ore was cited in the literature as being probably of the age of the Hudson River shales (Smock, 1889, p. 14; Eckel, 1905). The Hudson River formation itself was a rather nondescript terrane, which proved to contain a variety of formations. The writer, when first visiting the iron ore belt of the Catskill quadrangle in a preliminary survey of the region, discovered graptolites on both sides of the iron ore belt and thereby arrived at the conclusion that the iron ore must be of Normanskill age (Ruede- mann 1931, p. 136). Careful mapping in later years with the assistance of T. Y. Wilson revealed the underlying beds as be- longing to the Nassau formation and the overlying to the Schodack formation, as well as the presence of a great overthrust fault by which the Lower Cambrian rocks had been pushed from the east upon the Normanskill formation, hence the graptolites close to the west. Some of this material was even later found to have been dumped there and in time overgrown, thereby forming an apparently natural outcrop. Toward the east the series is much abbreviated and the thickness decreased by many small thrust faults, producing a shingle block or sliced structure and bringing the Normanskill shale up on the eastern brow of the ridge. The series, though abbreviated, is, however, a normal one from west to east as seen along the Greenfield road (see figure 21) save for the Bomoseen grit which is hardly sug- gested in the section. The series begins with the Normanskill grit, passes through the main overthrust fault, the Nassau beds, the Bur- den iron ore, the Schodack limestone and breccia, the Deepkill shale and the Normanskill shale and chert, the latter being the oldest divi- sion of the Normanskill. It is thus apparent that the Burden iron ore is a bedded layer hold- ing a horizon near or at the base of the Schodack formation and [47] Figure IS Adits of the old Mt Tom mine. The ore bed reaches to the roof of the adit on the left and to the projecting point in the side wall of the other. The overlying beds are calcareous grit. (E. J. Stein photo, 1935) GEOLOGY OF THE CATSKILL QUADRANGLE 49 above the Nassau beds. Its thickness is variable, partly because of the slip-planes, as we saw before, and partly perhaps due to rapid variation of original deposition. Smock reported a thickness of 41 feet including a thin bed of sandstone at the Burden mines (mines No. 3 and 2) southeast of Mt Tom; on Cedar hill a thickness vary- ing from eight to 30 feet, in the Livingston mine east of Cedar hill 18 feet and in the Plass Hill openings ore ranging between 10 and 16 feet with a footwall of drab-colored shale. The Burden iron ore is, as was early recognized by Dana (1884) and his successors in the study of the iron ores of eastern New York, of the same type as the iron ore of the great belt in the Harlem and 50 NEW YORK STATE MUSEUM Stockbridge valleys along the New York-Massachusetts line in the Taconic area. There is everywhere a capping of brown ore, the limo- nite which was mined and which at greater depths passed into sider- ite, the “white horse” or “dead head” of the miners. Altogether there are some 40 or 50 mine openings in this belt extending from Pittsfield, Mass., south along the interstate boundary to near Pawling, N. Y., in the two limestone belts on either side of the Mt Washington ridge. The age of these limestones, the Stockbridge limestone and the adjoining phyllites and schists is not exactly determined on ac- count of the metamorphosed condition of the rocks. A hasty survey of the mines on the New York side with Dr D. H. Newland, however, gave evidence that the schists close to at least some of the mines are metamorphosed Nassau beds and the limestone metamorphosed Schodack beds, in part at least ; the iron ore holding a place approximately between the two. This is especially apparent at Amenia, “one of the few places where the ore and wall rocks are well exposed ; the succession across the dip from footwall to hanging wall is : limestone-ore-mica schist ; with limestone repeated again to the east, above the schist” (Newland, 1936, p. 146). It was at Amenia that Doctor Newland and the writer were strongly impressed with the similarity of the schist with the Nassau beds of the un- metamorphosed belt and of the limestone with the quartzitic lime- stone of the Schodack formation farther west. Further, more accurate age determination of the eastern metamor- phosed beds will therefore probably prove that the Burden iron ores and the eastern iron ores not only have a like composition but also a like stratigraphic position and are parts of an identical horizon. It is in this connection interesting to observe that the eastern iron ore belt is interrupted north of Copake exactly opposite or directly east of the Burden-Church Hill belt by a stretch of about the same length as the latter belt that has no iron pits and apparently no iron. It is then quite possible that the Burden-Church Hill belt is a sector torn out of the eastern belt and carried farther west by about 15 miles on the overthrust plane that is exposed along the western slope of the ridge. The fact that east of the Lower Cambrian iron ore belt the Normanskill chert of Lower Normanskill age is exposed in contrast to the Upper Normanskill grit, that underlies the overthrust plane in the west, lends strength to this assumption of a possible far trans- ference of the iron ore belt and is further supported by the appear- ance of the overthrust plates of Lower Cambrian between the east- ern and western iron ore belts. [51] Figure 17 Abandoned workings in the ore bed and former adit on Plass hill, now filled in. The ore bed extends from the bottom to the projecting bed of calcareous grit. A stratum of shale in the ore bed is seen above the figure at base of outcrop. (E. J. Stein photo, 1929) [52] Figure 18 Contact, marked by hammer, of Nassau shale and quartzite on right and massive Burden iron ore on left. Cut in Greendale Station — Greendale road, looking south. (T. W. Graham photo, 1935) GEOLOGY OF THE CATSKILL QUADRANGLE 53 Origin of the iron ore. Besides the problem of the age of the Burden iron ore, another moot question is that of the origin of the iron ore. Various attempts have been made to answer the question. The ore consists of siderite and limonite, but it is generally understood that the limonite is an alteration product of the siderite, as the latter alone is found in the deeper and fresher portions of the ore bed. The problem revolves therefore about the origin of the siderite. Newland (1936, p. 151) gives the following resume of the views expressed on the origin of the ore : Dana regarded the siderite as a primary ore mineral and the de- posits to be part of the sedimentary succession, closely related to the Stockbridge limestone. Besides siderite, which seems to have with- stood decomposition to a marked extent, the original ore bodies may have contained isomorphous mixtures of iron, magnesia and lime car- bonates, combinations that would more readily succumb to weathering attack. The age of the sediments is held to be Ordovician. Kimball explained the siderite ore near Hudson, which he recog- nized to be conformably interbedded in the stratified series, by de- position of ferric oxide in the evaporating waters of inshore basins along with organic matter and detritus. Later burial, with reduction of the ferric oxide in the presence of hydrocarbons, led to the for- mation of an interbedded layer of siderite ; this mineral perhaps also replaced the wall limestone to some extent. He was the first, ap- parently, to recognize the possible relation of organic matter to the ore deposition. Smock remarked the presence of iron carbonate in the deeper work- ings of some of the Taconic pits. He considered the carbonate to be the source of the hydrous oxides. Eckel, in an introductory paper, not since extended, considered siderite the chief source of the limonite. Of the origin of the siderite he remarks that it was “deposited from solution and as a replacement of the limestone and not deposited in a basin contemporaneously with the inclosing rocks.” Certain deposits where siderite is not visible in the pits ( e.g Davis mines, Lakeville, Conn.) may have been formed by direct deposition of limonite from circulating underground waters. Hobbs developed the replacement idea further by considering the limonite and the carbonate as separate depositions, the one as replace- ment of the Berkshire schist and the other as replacement of the Stockbridge dolomite. The iron, in his view, came from some out- side source, not from alteration of the ferruginous minerals in the immediate wall rocks, carried in solution as ferrous carbonate and sulphate. The time of ore deposition was probably late Glacial or post-Glacial. On that point no convincing evidence is provided and it is difficult to find any in the field. Chance, in a broad generalization on the origin of the Appalachian 54 NEW YORK STATE MUSEUM limonites — a thesis which leaves out of account most particulars about their geology and mineralogy — characterized them as gossans, the weathered outcrops of buried pyrite bodies. It is hard to find any factual support for the explanation from occurrences anywhere in the Taconic belt, although it is known of course that some deposits of the gossan type are found in the Appalachian region, notably in Virginia, North Carolina and Tennessee. Such, however, have quite different features from the usual run of Appalachian limonites, so as to be differentiated without much difficulty when they are explored or mined. Kimball’s view prevailed until recent time. The writer ( 1931, p. 144) from a study mainly of the conditions surrounding the iron ore beds and the gross characters of the ore arrived at the view that the siderite may be an alteration product produced under the influence of the chemical mass action of the surrounding calcite upon magnetite that was brought down from the Precambrian heights in the east, which are a continuation of the Hudson highlands, where magnetite is still present in great abundance as in the 40-foot bed of the Tilly Foster mine. This magnetite was considered to have been deposited along the shore similar to the magnetite deposits found today along ocean shores and thereby to have produced the very elongate ore beds. A grant which the writer received from the Penrose fund of the Geological Society of America for the study of the iron ores* and chert beds of the Hudson River terrane allowed the manufacture of a series of thin sections of the limonite and siderite ore which were turned over to Doctor Newland for study. He arrived at the view expressed in the following summary (Newland, 1936, p. 152-54) : Microscopic examination, together with other information here brought out, gives new insight into the relations of the Taconic iron ores and the conditions of their origin. It may be remarked that the present study covers the occurrences in New York, Massachusetts and Connecticut, but not those of Vermont, for which appropriate material has not been available. The limonitized ores have a common heritage of characters due to their derivation from siderite as the principal source mineral. Siderite upon weathering yields rock limonite, which, like the former, occurs in bands or lenses intercalated conformably in the series of limestone and schists. The soft or wash ores are a step removed, as they con- sist for the most part of the reworked outcrops of the hard limonite, supplemented to some extent, perhaps, by iron derived from leaching of pyritic bands in the schists. Between unaltered siderite at one extreme and the thoroughly oxidized ore at the other, every stage in * An article on the age and origin of the Burden iron ore, delivered to the Geological Society in March 1935, has not been printed and most of the facts here presented are taken from that article. [55] Figure 19 Picture continuous with preceding figure. Outcrop of Schodack limestone, partly brecciated, overlying the iron ore. Small steep fault in center. (J. W. Graham photo, 1935) Figure 20 Thin section of Burden iron ore, showing idiomorphic siderite crystals, forming a nodule at upper right and rounded, frosted quartz grains (white). (E. J. Stein photo) [56] GEOLOGY OF THE CATSKILL QUADRANGLE 57 the progress of weathering may be observed in samples collected from the mine pits. Rock limonites, owing to their inheritance of textural patterns and incidental mineral components of the originals, lend themselves to petrographic analysis for mutual comparisons and de- ductions as to origin. Of the nature of the siderite bodies the evidence is conclusive for the Hudson occurrences in the western part of the Taconic belt. There the ores have been deposited as contemporaneous sediments of probably early Cambrian age. They have a stratified structure which extends to the finer layering of constituents. The siderite is in uni- form crystal shapes and is associated with amorphous silica and plentiful organic matter in the form of diffused hydrocarbon, which latter produces a resemblance to black-band ore when concentrated, as it sometimes is, in definite beds. Well-rounded quartz, feldspar cleavages and silt compose the clastic sediment. Definite sedimentary traits of texture and structure are rarely dis- cernible in the eastern part of the ore belt because the deposits have shared the more intensive compression and metamorphism which characterize that area. It is obvious from this circumstance that the deposition of the siderite preceded the Taconic upheaval. Further, they show so many similarities — mineral, chemical and other — with the western deposits that little doubt arises that the eastern bodies are actually members of the same group formed under similar condi- tions. Mineralogically, the lack of amorphous silica and the presence of secondary sericite constitute the only distinctive features of the eastern ores, as compared with those found near the Hudson river. Brecciation, mashing and metamorphism become more manifest as one crosses the Taconic belt from west to east. The ores follow the country in that respect. The clay shales of the western area give place to phyllites and to mica schists on the New England border. The manner in which the iron was collected and precipitated in the known associations and traits is a problem by itself. The oc- currence of euhedral siderite with amorphous silica and organic matter in the described relations has few counterparts among the better known iron ore deposits. The nearest analogy seems to be with the clay ironstone and black-band ores of the Carboniferous. There is little to be found in literature, at least within the writer’s ac- quaintance, about the microscopic features of those ores, but it is inferred that the iron ore occurs as crystallized siderite with primary relations. Small amounts of manganese and traces of lead and zinc (rarely copper, nickel and cobalt) are indicated by analyses. So far, the resemblance is close. But the Taconic ores have only a minor content of clay and locally, at least, contain substantial amounts of colloidal silica. Further, the Taconic siderites attain a thickness of fully 40 feet, possibly more, in a single bed, much greater than the run of ironstones or black-band ores of our coal measures. The deposition of the siderite took place most likely in lagoons or in-shore basins, which received wash from the land from time to time, as well as a steady influx of iron in solution. That the iron was carried as ferrous bicarbonate seems probable. The abstraction of the sol- 58 NEW YORK STATE MUSEUM vent carbon dioxide by organisms, probably vegetable, caused pre- cipitation, and the presence of free hydrocarbon has been one of the factors in preserving the iron in ferrous form. That the siderite crystallized before and not after precipitation is surmised from its relations with the silica. Abundant stores of iron in the form of silicates and oxides were released by erosion of the crystalline formations in late Precambrian time. The ferruginous minerals were largely decomposed and the iron taken into solution, for they do not appear to any notable extent as mechanical ingredients of the Cambrian sandstones and shales. Antecedent conditions, thus, may be held to have been favorable to the accumulation of chemically precipitated iron ores in the early Cambrian. The relation of the Taconic district to the rest of the Appalachian district from the standpoint of the origin of the limonites is a sub- ject for future examination. The outcome may be important for stratigraphy as well as economic geology. For the present it suffices to refer to the many striking comparisons between Taconic and other ore occurrences available in the published records, suggestive of a community of physical and chemical features hardly realizable from the operation of mere chance. We thus see that the final microscopic analysis of the siderite ore supports Dana’s original view of the siderite, being a primary ore mineral. The presence of numerous sand grains floating in the matrix at the Burden and Church Hill mines, as well as of numerous angu- lar pebbles making a breccia of part of the ore indicate the deposition in water that was advancing and receiving also wind-blown material from the land. The large Nassau-quartzite slabs incorporated in the ore and mentioned before suggest that the sea advanced over old land with Nassau beds exposed on the surface. It is very probable that the appearance of the iron ore between the Nassau and Schodack beds has a much greater significance than would appear from the mere local occurrence in eastern New York. Doctor Newland has already hinted in his closing chapter at “the many striking comparisons between Taconic and other ore occur- rences available in the published records, suggestive of a community of physical and chemical features hardly realizable from the opera- tion of mere chance.” An attempt at a correlation of the Lower Cambrian formations of the entire Appalachian geosyncline from Newfoundland to Ala- bama brings out the fact, as was pointed out to the writer by Dr Charles E. Resser, a leading student of the American Cambrian faunas and stratigraphy, that the base is everywhere formed by quartzitic beds, pure quartzite or quartzite and shale and that this GEOLOGY OF THE CATSKILL QUADRANGLE 59 60 NEW YORK STATE MUSEUM is later followed by Lower Cambrian calcareous beds or frequently by limestone and shales. It thus appears that the quartzites and shales which we have called Nassau beds and Diamond Rock quartzite (Troy quadrangle) and the limestones, dolomites and limestone breccias with shales which we have termed Schodack and Troy beds (which will be united, see later page) may well be continued as Cheshire quartzite at the base and the overlying Plymouth marble and Plymouth breccia in south- eastern Vermont, or Cheshire quartzite and Rutland dolomite and Cheshire quartzite with overlying Monkton quartzite ( fossiliferous), Winooski marble and Mallett dolomite above in northwestern Ver- mont. We do not cite in this connection the smaller members of less wide distribution, as the Bomoseen grit and the Mettawee slate which will be considered as members of the Schodack formation in a later chapter (see page 65). The Cheshire quartzite extends to Vermont (see Wilmarth correlation table of Vermont) and the series can be recognized in Canada and Newfoundland, where the Nassau beds are represented by the Random terrane of Walcott (fide Resser). The Random terrane was considered by Walcott (1900, p. 3-5) as of Algonkian age and is still placed with the Precambrian. The im- portance of this correlation will be understood when it is remembered that the Nassau beds, as well as the Cheshire quartzite and other basal quartzites have thus far utterly failed of affording any fossils save the Oldhamias in New York, which are but feeding trails of soft-bodied animals (supposedly worms) and might equally well occur in Precambrian beds of the Beltian type. T. H. Clark (’21) has also found barren beds (slate, dolmite and graywacke) below the Cheshire quartzite in southern Quebec and north of Vermont. It is possible that also these beds are Precambrian in age. Also southward from the Hudson valley the sequence of the basal quartzite and shale and superjacent limestones and shales is pre- served. The Nassau quartzite is continued southward in the Poughquag quartzite of the Highlands and the Cheshire quartzite of the Taconic range which there is followed by the lower Stock- bridge limestone. South of New York in New Jersey the base is formed by the Hardyston quartzite with the Lower Cambrian (Olenellus) fauna in the upper part which is overlain by the Kit- tatinny limestone, that has Upper Cambrian fossils above the middle and is barren in the lower part. The Hardyston series of quartzites (with various members, Loudoun formation, Weverton sandstone, GEOLOGY OF THE CATSKILL QUADRANGLE 61 Harpers schist with Montalto quartzite member) and the overlying Antietam sandstone in central southern Pennsylvania and the cor- responding basal Chickies quartzite with Hellam conglomerate mem- ber at bottom in northeastern Pennsylvania are followed by Lower Cambrian limestones (Tomstown dolomite). In Maryland and northern Virginia we find again the Loudoun, Weverton, Harpers, Antietam quartzite and shale series overlain by the Tomstown dolomite, while in central and southwestern Virginia these formations appear in slightly different character but the same general succession in ascending order as Unicoi sandstone, Hampton shale, Erwin quartzite, Shady dolomite and Watauga formation or shale (Rome formation in west, upper part Middle Cambrian), while in the Blue Ridge province of North Carolina the typical Unicoi formation (a 1500 to 2500 foot massive white sandstone, feldspathic sandstone, and quartzite, with interbedded shales in upper part and conglomerate arkose and graywacke in lower part) is fol- lowed by the Hampton shale, Erwin quartzite and Shady dolomite and their differently named correlatives, and the Piedmont plateau contains corresponding metamorphics (Kings Mountain quartzite, Blackburgs schist and Gaffney marble). The succession can be fol- lowed to Alabama, where the barren Weisner quartzite, Shady lime- stone and Rome formation (shales) represent the Lower Cambrian series. If in the Lower Cambrian of the Appalachian geosyncline a gen- eral succession of basal quartzites and shales and overlying limestones and shales can be established, as is indicated by the preceding survey, it is equally probable from information the writer has received from students of the Lower Cambrian, as Dr Charles E. Resser, and of its economic products, as Dr D. H. Newland and Professor A. F. Buddington that the siderite-limonite iron ores are usually found in the quartzite-limestone interval of the formations. We may add that this work may receive still greater significance from the possibility that the iron ore horizon may mark the end of the Precambrian era. This is suggested by several facts, first of which is the absence of fossils in the Nassau quartzite and corresponding basal quartzites; further the apparent transition of undoubted Pre- cambrian beds into the basal quartzite series, as in the Random ter- rane, and finally the fact that widely-spread iron ore deposits are beginning to be considered as evidence of long preceding continental emergence and erosion, which furnished the iron-solutions to the continental and littoral waters. This view is especially prevalent 62 NEW YORK STATE MUSEUM among European students of sedimentation problems, as Johannes Walther (1893) and Hermann Schmidt (1935). If the Nassau beds, like the supposedly correlated Random beds of Newfoundland, should prove to be of Precambrian age (Resser) the Burden iron ore horizon would be on the actual boundary of the Precambrian-Cambrian eras (Lipalian interval) and in a true position to be regarded as the result of the washing out of the regolith of the widely emerged continent. In case the Nassau beds should prove, however, to be of earliest Lower Cambrian age, it would still be pos- sible to consider the iron ore of a like origin, as also in Lower Cam- brian time the largest portion of North America was still widely emergent. It is in this connection important to remember that the Bomoseen grit which holds about the same horizon as the Burden iron ore, is a peculiar arkosic rock, a coarse grit, full of hematite scales and with a considerable number of plagioclase grains. This rock with its iron and feldspar content points also to a continental surface with much granite as the source of the material, presumably also a Precambrian surface and suggests even the character of a continental regolith similar to the Brayman shale. Schodack Formation In Bulletin 169 (Saratoga-Schuylerville quadrangles, 1914, p. 69) the writer proposed the following names for recognizable larger units of the Lower Cambrian in the Schuylerville area: GEOLOGY OF THE CATSKILL QUADRANGLE 63 The Lower Cambrian Series as Exposed in Rensselaer County and Part of Columbia County, N. Y. Name of formation Serial letter Description of strata Fauna Estimated thickness in feet Schodack shale and • limestone Troy shale j Diamond ( Rock < quartzite [ Bomoseen J grit | J I Greenish shale. Thin-bedded limestone or dolo- mitic limestone in varying alternations with black or greenish shale and calcareous quartz sandstone. Some of the limestone beds brecciated within the sandstone or shale and forming brecciation peb- bles, in places, however, beach pebbles. Olenellus fauna 50 a 20-200 H Greenish, reddish, purplish shale, in places with small beds of more or less calca- reous quartzite. Oldhamia, an- nelid trails Hyolithes and Hyolithellus 25P-100 + G F Granular quartzite, in places a calcareous sandstone. 10-40 Olive grit, metamorphic, usu- ally weathering reddish; absent at south. Traces of? 18-50 E Greenish , or reddish and green- Casts of impres- 65-535 ish, shale with small quart- sions, zite or grit beds. b Oldhamia D Massive greenish quartzite, in 10-50 places very coarse. Nassau C Reddish and greenish shale Casts of impres- 30-80 beds 1 with small beds of quartzite siong, or grit (rarely up to five feet Oldhamia thick). B Massive greenish quartzite, in 8-40 places very coarse. A Reddish and greenish shale with Casts of impres- 50-80 small beds of quartzite or sions, grit, from one to 12 and, Oldhamia rarely, 24 inches thick. a Usually SO. b Oldhamia occurs in A, C or E, and quite possibly in all three. Minimum, 286. Maximum, 122S+. For the sake of completeness the following terms were proposed: Mettawee slate for Dale’s Cambrian roofing slate, Eddy Hill grit for his Black patch grit and Zion Hill quartzite for the ferruginous quart- zite. These were not found far south of the New York- Vermont line and apparently are absent in the Schuylerville area. 64 NEW YORK STATE MUSEUM On the Troy and Cohoes quadrangle of the Capital District (Bui. 265, p. 79, 1930) the writer recognized in descending order: Schodack shale and limestone Troy shale and limestone Diamond Rock quartzite Bomoseen grit Nassau beds It was, however, very difficult, owing to the intricate folding, to separate the Schodack, Troy, Diamond and Bomoseen formations on the map and therefore not undertaken. They were, therefore, united into an upper division in distinction to the lower or Nassau division and these two divisions were mapped. The Diamond Hill quartzite is only a very local formation that has been seen only in one outcrop. It may be, as suggested to me by Doctor Resser, the result of a hot spring that flowed in Schodack time and be in line with similar thick local quartz deposits farther south in the Appalachian geosyncline. On the Catskill quadrangle it was possible to distinguish in de- scending order: Zion Hill quartzite Schodack shale and limestone Burden conglomerate Grabau Bomoseen grit Burden iron ore Nassau beds Again the Zion Hill quartzite, the Schodack shale and limestone, the Burden conglomerate and the Bomoseen grit were so intimately connected and inter folded that it would require much more detailed work than the writer could give to the quadrangle and a larger scale map to attempt to separate these divisions. In a conference with Doctor Resser it was found that it would be more practicable to extend the term Schodack formation so as to include as members the beds that occur associated or even interbedded with it such as the Zion Hill quartzite and the Burden conglomerate, and also the Troy shale and limestone, which is for the most part a mass of greenish, reddish and purplish shale in places with small beds of more or less calcareous quartzite. This formation can then be correlated with the larger upper units of the Lower Cambrian north and south of New York, which also consist of limestones and shales. Prindle and Knopf (1932, p. 277) GEOLOGY OF THE CATSKILL QUADRANGLE 65 have been able to distinguish on the Taconic quadrangle (including the Berlin and Hoosick quadrangles east of the Capital District) the Mettawee slate, the Schodack formation and the Eagle Bridge quart- zite which they consider as probably identical with the ferruginous quartzite (horizon C) of Dale (Ruedemann’s Zion Hill quartzite), but name separately as the correlation is not certain. Doctor Resser would unite Ruedemann’s Mettawee slate, Schodack shale and lime- stone and the Eagle Bridge quartzite (Zion Hill quartzite) into the Schodack formation and correlate this with the ever-present upper limestones or dolomites and shales of the Lower Cambrian, that is with the Parker shale and Mallett dolomite of Vermont, the lower Kittatinny limestone of New Jersey, the Tomstown dolomite of Penn- sylvania and northern Virginia, the Shady dolomite and Watauga formation (Rome formation in west) of North Carolina, known as the Shady limestone and Rome formation of shales as far as Ala- bama. Doctor Resser would also correlate the Bomoseen grit and Dia- mond Rock quartzite with the Antietam quartzite and Erwin quart- zite of the South. In his last publication (’38, p. 6) the Antietam quartzite is considered as represented in New Jersey by the Hardy- ston quartzite and in New York by the Poughquag quartzite and the Bomoseen grit of the Hudson valley. We have already pointed out, in the chapter on the Burden iron ore, the importance for general paleogeographic conclusions that this uniform series of shales and quartzites, followed by shales and limestones, has in the Appalachian geosyncline. It is worth noting that the Shady dolomite of Georgia and Vir- ginia, as well as the Mallett formation of Vermont are remarkable for the beautifully developed reefs of Archaeocyathinae with which is usually associated a rich fauna. No such reefs were clearly seen in the Schodack formation of the Catskill district, but they may well be present and only have failed to be exposed as a result of the scanty outcrops. Zion Hill quartzite member (ferruginous quartzite). The fer- ruginous quartzite is exposed as a deep iron-red quartzitic sand- stone in many localities on the Catskill quadrangle. It is one of the most striking rocks of the Lower Cambrian there. Dale (1899, p. 183) gave a careful description of this formation as it appears in the New York- Vermont slate belt. It may reach there 74 feet in thick- ness, but is more often between 10 and 30 feet thick and lies between the Lower Cambrian black slate and the Ordovician black slate. It 66 NEW YORK STATE MUSEUM appears in the central and southern part of the slate belt as a mas- sive quartzite, which “is vitreous with brown limonite specks in the cement, probably from the alteration of a siderite. It there is identi- cal in composition and appearance with the quartzite of Horizon A (Bomoseen grit). In other places, however, it is a bluish calcareous sandstone, the grains being quartz (with a few of plagioclase and microcline) and the cement calcareous and sideritic. The rock is traversed by numerous quartz veins, sometimes very thin. In weather- ing the calcite carbonate is dissolved away, the siderite (FeCo3) passes into limonite, giving a rusty color, and the rock gradually crumbles back into quartz sand, while the quartz veins remain.” It is interesting to note that Dale considers it identical in com- position and appearance with the Bomoseen grit which lies at the base of the Schodack formation. On the other hand it is so similar to the Burden iron ore, that Kimball in his section of the siderite basins (see figure 14) continued the Burden iron ore horizon east- ward to outcrops of ferruginous quartzite (sections D and F on Charles Miller’s farm, section H-l on Morris Miller farm). In its composition of quartz grains, and a matrix of calcite and siderite it is to be considered as a reappearance of the conditions that produced the Bomoseen grit and in their fullest development the Burden iron ore. That the ferruginous quartzite is actually a weathered gray to white quartzitic limestone is well shown in outcrops about a mile southeast of Germantown, where in the woods vertical ledges of this hard fresh rock were found with weathered crusts two to three inches thick of typical ferruginous quartzite*. The bed is here found be- tween 20 feet of compact limestone and gray slate. In most cases, however, it is closely associated or alternated with calcareous breccia ; west of Bull pond it was found intergraded with breccia, the section being there in descending order : 3 feet gray quartzite with ferruginous quartzitic walls 2 feet breccia 4 feet ferruginous quartzite gray quartzite On Claverack creek, at the southeast corner of the Becraft Moun- * A very similar case of alteration of a rock that has been only recently recog- nized in its true nature is described by P. Dorn (1936, p. 289). He found that rock exactly identical with the deep red Eisensandstein des Dogger B (iron- sandstone of Dogger), a widely spread iron ore and a good Jurassic counter- part of the ferruginous quartzite, originates from pyritiferous calcareous sand- stone and dark clay shales by decalcification and oxidation of pyrite. GEOLOGY OF THE CATSKILL QUADRANGLE 67 tain outlier one sees the following section from the top of the hill down to the creek (47 feet) Greenish gray shale with many thin quartzite bands Ferruginous quartzite and red soil Breccia 5-f- feet thick, forming waterfall Greenish gray shale in creek below fall The breccia was described by Grabau (see page 76) as Burden conglomerate. Outside of the Catskill quadrangle just south of the village of Claverack a coarse conglomerate is found in Schodack beds that con- tains numerous ferruginous quartzite pebbles and other limestone pebbles. This bed which is incorporated in greenish gray siliceous slates with numerous black worm-tubes represents a horizon above the Zion Hill quartzite or ferruginous quartzite and indicates that this member in this area does not form the top of the Schodack formation, but is only a member near the top. Very interesting sections were found on the road leading south from Elizaville. Here at a farmhouse were noticed in descending order (see figure 22) : Thin-bedded limestone Yz foot conglomerate 3 feet ferruginous quartzite 10 feet thin-bedded limestone and shale 10 feet -j- greenish gray and black shale and thin quartzite Figure 22 Section of Schodack beds along road south of Elizaville 68 NEW YORK STATE MUSEUM A quarter of a mile farther north there were found on the hill- side : 2 feet ferruginous quartzite 15 feet covered 10 feet olive grit, weathering reddish Thin-bedded quartzite Thin-bedded limestone and black shale On the ridge east of the New York road, half a mile southeast from the southwest corner of the Becraft Mountain outlier three feet of ferruginous grit is exposed on top of a 12-foot bed of Schodack conglomerate and the ferruginous grit is well shown in the quarry on the opposite side of the road, half a mile south. Along the north-south road one and one-fourth miles southwest of Bingham Mills a most instructive section was found in nearly vertical beds going from west to east in the following order (see diagram, figure 23) : White weathering chert (west of road) Black shale with graptolites (east of road) Breccia Ferruginous quartzite Heavy limestone Ferruginous quartzite Breccia Here in a small anticline the incorporation of ferruginous quart- zite between heavy limestone and breccia is distinctly shown. One and one-fourth miles southeast of Germantown near the east- west road a succession of 10 feet of conglomerate and breccia, six feet of ferruginous quartzite and six feet of drab quartzite with some intervening shale was found. A similar succession was observed a mile farther east. Finally in the Greendale section about 75 feet of Schodack lime- stone breccia and conglomerate are exposed between the Burden iron ore and a small wedge of ferruginous quartzite caught in a fault that separates the Schodack from the Deep kill (see figure 21). It is thus obvious that near the top of the Schodack formation is a series of limestone beds, breccias and conglomerates and one or two beds of quartzitic limestone, weathering into ferruginous quart- zite. The basal beds of the Schodack series are exposed at the Burden iron mine, where as we saw before (see figure 16) the Nassau quartzite is overlain by 25 to 40 feet of iron ore, 6 feet of thin- GEOLOGY OF THE CATSKILL QUADRANGLE 69 Figure 23 Section along road southwest of Bingham Mills, showing relation of edgewise conglomerate and ferruginous quartzite to Schodack limestone and shale 70 NEW YORK STATE MUSEUM bedded quartzitic limestone, 13 feet of heavy-bedded gray quartzitic limestone, 5 feet of thin-bedded quartzitic limestone and 20 feet of brownish to orange weathering very massive quartzitic limestone. These beds are also exposed in the Greenfield road cut with con- siderable breccia. There is very much greenish gray shale intercalated between the basal limestone and these rocks at the top. These shales often con- tain many thin limestone beds. Fine exposures of this middle portion of the Schodack beds are found along the new road cut of the New York road (Route 9E) just south of the Becraft Mountain outlier and in Fisher’s quarry (one and one-half miles due southeast of Germantown (see figures 24-28). The cut along Route 9 gives a fine exposure of the series of rocks, beginning at the left with alter- nating black shale and thin limestone bands. This series up to five feet thick, is usually capped by a heavier limestone bed (about one foot) that is followed by black shale (two to five feet thick), upon which rests again the thinly bedded alternating shale and limestone. The diagram (figure 28) shows clearly that we have here a fourfold regular upward succession of black shale, black shale with thin lime- stone bands and a heavy limestone bed. This series indicates regu- larly and slowly proceeding changes from muddy water to clear water, which is abruptly filled with mud again. Whether these first gradual and later abrupt changes are due to a change of shore cur- rents, or merely of their velocity or indicate the oscillation of a barrier is difficult to establish from the data at hand. One of two facts which are suggestive in this connection is the presence of lenses of edgewise conglomerate on top of the heavy limestone beds. Five of these lenses can be discerned in the section. The lenses consist of angular, little, crowded, more or less erect slabs of thin limestone, forming thus a typical edgewise conglomerate or rather breccia. These lenses indicate that submarine slumping took place at the bottom of a gently sloping seacoast, involving recently hardened calcareous mud beds. The repeated presence of these lenses at the same horizon, vis., at the top of the heavy limestone, followed by black shale, points to the recurrence of violent interruptions by storms, earthquakes or other agents that caused the slumping and new inrush of muddy water. Such lenses of edgewise conglomerate are also seen in Fisher’s quarry (see figures 24 and 25), here again on top of a heavy lime- stone bed, a foot thick, that is followed by very thin-bedded black shale and limestone, which is directly followed again by heavy limestone, [71] Figure 24 Schodack beds in Fishers quarry, two miles southeast of Germantown. Heavy limestone beds alternating with black shale are exposed. The figure in the iniddle points to a lens of edgewise conglomerate, that lias termed in thin-bedded limestone and shale. See next figure. (E. J. Stein photo, 1935) a q c o o-g p< a p c U)‘S .5 c/) be . P O ^ .£ *0 fo g o3 be p £3 172] [73] Figure 26 Road cut on Highway 9, one mile southeast of south end of Becraft mountain. Shows alternating thin limestone strata and black shale; also lenses of edgewise conglomerate; some above the figure on the right, another behind the figure on the left and one in the middle. Schodack beds. (J. W. Graham photo, 1935) [741 Figure 27 Enlargement of two lenses. The brecciated character of the limestone is more distinct in the upper lens in this picture. (J. W. Graham photo, 1935) GEOLOGY OF THE CATSKILL QUADRANGLE 75 76 NEW YORK STATE MUSEUM the black shale bed being absent in this case, but present above and below the horizon of the lenses. Identical lenses of edgewise conglomerate are also known from the Deadwood formation (Upper Cambrian) of the Black hills. It is considered by Schuchert and Dunbar (’33, p. 157) as made up of the shingled-up fragments of mud-cracked layers. The more extensive beds of edgewise conglomerate, described before by Dale and Prindle and by the writer from the Schodack limestone beds in Albany and Washington counties, may in part at least have originated on tideflats where such beds are seen forming today when partly consolidated thin limestone beds are again broken up as Hantschel (’36, p. 350) shows from the German coast of the North sea. On the other hand, lenses of edgewise conglomerate as those in Fisher’s quarry and south of Becraft mountain that clearly repre- sent a slipping at times on a firmer bed, if they can be found over a wider area at the same horizon — as those at the two mentioned locali- ties may be— suggest seismic activity that caused sudden slipping of portions of the slanting sea bottom that were in more labile condition. Another fact worthy of notice here is the presence of numerous rounded sand grains in the limestone and also in the breccia. These sand grains are nearly always smoky or black quartz and Doctor Newland tells me that very little smoky quartz occurs in the Adiron- dacks but that it is found farther east (see Emerson). We therefore seem to have here an indication that these sand grains were blown in from the east and that the deposition of the beds took place along the eastern shore of the geosyncline, a conclusion that agrees ex- ceedingly well with the presence of the Schodack limestone only in the eastern or Levis trough of the Appalachian geosyncline. Inci- dentally it may be mentioned that the Rensselaer grit also contains much smoky quartz, indicating its derivation from areas east of the Adirondacks. The Lower Cambrian beds of limestone, breccia and edgewise conglomerate all contain numerous rounded grains of quartz, mostly of the smoky variety. The presence of this quartz has been fully described before by Dale and the writer. Burden conglomerate. The limestone breccia beds of the Schodack formation attain considerable thickness, beds measuring 12 feet having been seen. Still greater thicknesses were observed in Ver- mont and northeastern New York. Grabau (1903, p. 1034) has described this conglomerate which he correlated with the Norman- skill as follows : GEOLOGY OF THE CATSKILL QUADRANGLE 77 This name is proposed for a calcareous conglomerate in which the pebbles are chiefly limestone embedded in a silicious sand, which in turn is held together by a more or less calcareous cement. The limestone of the pebbles is in part a gray, compact rock (calcilutite) not unlike the Manlius limestone and in part a more granular mass ( calcar enite [Grabau]). The matrix is generally stained with iron hydrate and at the Burden iron mine this rock is in intimate associ- ation with the iron ore. Davis described this rock, assigning to it an age “apparently younger than the Helderberg series, and certainly much older than the drift.” He thought that the limestone fragments “seem to cor- respond with the several subdivisions of the Lower Helderberg.” He found it at two localities, one in the meadow south of Academy hill and one in the fields a quarter of a mile south of the southern end of the mountain. It is well exposed on a little stream which enters Claverack creek at a point about east of that where fault 16 strikes the eastern bounding road of the mountain. The stream lies on a fault line. It has cut back some distance from Claverack creek and forms a fall over the hard conglomerate, which fall has been utilized as a site for a dam and mill. The conglomerate bed is about 10 feet thick at the fault. It dips northeastward and abuts against what are probably the Normanskill shales, which have a similar dip. The conglomerate increases in thickness away from the fault and forms a prominent hill between the road and the stream. It is under- lain by shales similar to those on the opposite side of the fault. The age of this conglomerate is unknown. That it belongs to the Hudson River series is undoubted, but whether older or younger than the Normanskill shales, has not been ascertained. No fossils have been noted in the pebbles of limestone, though some search has been made for them. The position and character of the bed indicate that the rock is older than the beds composing Becraft mountain, for all these beds with the exception of the Manlius are highly fos- siliferous and easily recognizable. It may correspond to the Trenton conglomerate of Rysedorph hill described by Ruedemann, or it may be of still earlier date. Its areal relations seem to indicate that it is older than the Normanskill beds of Mt Moreno. Boulders of this rock have been found on Becraft mountain in such a location that they could not well have been derived from any known outcrop. They therefore suggest other outcrops to the north or northeast of Becraft mountain. It follows from his description and our field work that he has united under the name Burden conglomerate the beds at the Burden iron mine of earliest Schodack age with those of later Schodack age found at Claverack creek and north of Becraft mountain. All are, however, of Schodack age and not of Normanskill age. The Rysedorph conglomerate with which Grabau correlates the Burden conglomerate is also well represented on the Catskill quad- 78 NEW YORK STATE MUSEUM rangle and outcrops in great thickness north of Elizaville. It is of Middle Ordovician age (see page 116). The full thickness of the Schodack formation on the Catskill quad- rangle has not been ascertained. As usually only the limestone beds or the alternating limestone beds and shales are exposed, while the greenish gray and black shales which reach considerable thickness re- main hidden, the thickness of the formation is undoubtedly greater than would appear by piecing the various outcrops together. Out- crops of 25 to 50 feet of limestones with intercalated shales and representing different horizons, as do the outcrops at the Burden mine, Fisher’s quarry and the road cut at Route 9 with the hill- section behind it indicate nearly a hundred feet of limestones with shales. To this can be added more than a hundred feet of greenish gray and black shales, which are seen in several places, especially on the quadrangles north of the Catskill quadrangle. The fauna of the Schodack formation has been fully dealt with in the geology of the Capital District (Bui. 285). As the fossils proved rare and fragmentary in the shales and limestones, where the con- glomerate is the main carrier of them, it was not deemed necessary to make a special effort to collect them. We add here the list of the forms reported from the Capital District : Sponges : Archaeocyathus rarus (Ford) A. rensselaericus (Ford) Brachiopods Acrothele nitida (Ford) Acrotreta sagittalis taconica (Wal- cott). Bicia gemma (Billings) B. whiteavesi Walcott Billingsella salemensis (Walcott) Botsfordia caelata (Hall) Lingulella schucherti Walcott Micromitra ( Paterina ) labradorica (Billings) Obolella crassa Hall Obolus prindlei (Walcott) Yorkia washing tonensis Walcott Mollusks : Hyolithellus micans Billings Hyolithes americanus Billings H. communis Billings H. communis emmonsi Ford H. impar Ford Scenella retusa (Ford) Stenotheca rugosa (Hall) Trilobites : Elliptocelphala asaphoides Emmons Microdiscus connexus Walcott M. lobatus (Hall) M. schucherti Walcott M. speciosus Ford Olenoides fordi Walcott Protypus hitchcocki (Whitfield) Solenopleura nam Ford CANADIAN SYSTEM The Canadian System is represented in the eastern shale belt, or the eastern (Levis) trough of the Appalachian geosyncline in New York by some limestone (Bald Mountain limestone), the Schaghti- coke graptolite shale (Ruedemann, 1903) and the Deepkill series of graptolite shales (Ruedemann, 1902). The graptolite shales are well GEOLOGY OF THE CATSKILL QUADRANGLE 79 represented in the Capital District and their type localities are found on the Cohoes quadrangle. (The northeastern sheet of the Capital Dis- trict map.) The Bald Mountain limestone was discovered on the Schuylerville quadrangle (Cushing & Ruedemann, 1914) and not noted in the Capital District. A small outcrop has since become exposed by erosion on top of Rysedorph hill, but no exposures were found on the Cats- kill quadrangle and the limestone belt probably is intermittent, but is continued in the Wappinger limestone south of the Catskill quad- rangle. The Schaghticoke shale is characterized by the presence of Die- tyonema flabelliforme (Eichwald) var. acadicum (Matthew) and Staurograptus dichotomies (Emmons) var. apertus Ruedemann. This important guide horizon, which is now considered in America and most of Europe as marking the base of the Canadian (Beekmantown formation) or Ordovician (sensu lato) was formerly held to be the last Cambrian horizon and is still considered so by authors in Great Britain. The horizon has not been observed on the Catskill quad- rangle, which, however, by no means indicates its absence there, as the relatively small thickness of the beds (minimum measured 30 feet at Schaghticoke, probably considerably more) will serve to ob- scure their presence in the much folded mass of shales. Deepkill Shale The Deepkill shale and its faunas have been fully described by the writer in 1904; the type section at the Deep kill in Rensselaer county in 1902, and the outcrops and faunas of the formation in the Capital District in 1930. From the last record we quote the para- graphs here of interest : In 1902 the writer described as the Deep Kill shale the graptolite shales of Beekmantown age which he had discovered along Deep kill in Rensselaer county, N. Y., exposed in a continuous series of rocks. This splendid outcrop begins a quarter of a mile above the hamlet of Grant Hollow in the creek bed, and extends to the dam of the reser- voir of the Troy waterworks in the Deep Kill gorge. It has been very fully described in New York State Museum Bulletin 52 (also Volume 55, Report of the New Y'ork State Museum for 1901, p. 546-605, 1903), because it is the only complete section through the Beekman- town graptolite shale known as yet south of that at Point Levis, near Quebec. . . . It was estimated by the writer that the rocks of this section must have attained a total thickness of 200 to 300 feet. Dale (’04, p. 33), who has recorded some other outcrops of Beekmantown shale 80 NEW YORK STATE MUSEUM in the Capital District, roughly estimated the thickness in these locali- ties at 50 feet, but considers it a possibility that some of the green shales without banded quartzites and without fossils belong to this formation and therefore he holds his estimate to be a minimum. The Deep Kill shale is most characteristically represented by finely banded quartzite beds that in places are very calcareous and are as- sociated with greenish and grayish shales, resembling the lower Cam- brian shales. Along the Deep kill we have the following succession of rocks (the letters refer to the figure) : b Limestones (more or less silicious) with shaly intercalations c Sandy shales and grits d Greenish siliceous shale and black graptolite shales Graptolite bed 1 e Thin-bedded shales, grits and limestones f Greenish silicious shale and black graptolite shale. Graptolite bed Z g Greenish silicious shale h Thin-bedded, dark gray limestone i Greenish silicious beds and black graptolite shale Graptolite bed 3 j Greenish silicious beds and sandy shales (two thin seams of bluish black shale with graptolites) k Dark gray thin-bedded limestone layers / Greenish silicious beds and black graptolite shale Graptolite bed 4 m Thin-bedded limestone with shale partings n Covered o (Quarry) Two to three-foot banks of hard, fine-grained thin-bedded layers (banded greenish gray and lighter). Many tenuous grapto- litiferous partings of black shale. 52' Graptolite bed 5 q Covered (distance of 825') (100'+ ) r Exposure at north side of dam, 135 feet long, mostly greenish gray quartzite, with some brecciated layers and some thin bands of gray limestone (70' + ) Graptolite bed 6 (3') and graptolite bed 7 (2') Worth noting in this section is the appearance of a breccia and coarse-grained sandy shale in c, the uneven surface of the limestone layers in h, and the still more undulating or interlocking surfaces in k, and limestone breccia in l. Still more important is the distinct alternation of calcareous beds and siliceous and graptolite shales, indicating at least five cycles of deposition between b and o, either due to oscillations in the depth of the trough, or to changes in currents. The writer (’03) divided the Deepkill graptolite shales as exposed at the type locality, into three main zones, namely, a Tetragraptus zone, comprising graptolite beds 1 and 2 b Zone of Didymograptus bifidus and Phyllograptus anna, graptolite beds 3, 4 and 5. c Zone of Diplograptus dentatus and Cryptograptus anten- narius, graptolite beds 6 and 7. 4' 0" 2' 8" 0' 8" 1' 8" T 9" 2> 9" 14' 3" 2' 5' 5" 5' 9" 7' 4" 16' GEOLOGY OF THE CATSKILL QUADRANGLE 81 Later (’19, p. 119), the writer found it advisable to divide each of the zones into two subzones, since the graptolite faunas of the two or more graptolite beds of each zone show differences in their faunal composition that correspond to those recognized in other regions, notably Great Britain and Sweden. Furthermore, another zone below the deepest Deepkill zone exposed at the Deep kill is indicated by an occurrence, discovered by L. M. Prindle on the road between Defreestville and West Sand Lake (Dale, ’04, p. 30). This contains forms of the Clonograptus zone of Quebec and Europe. We have accordingly distinguished the following subzones in ascending order. (T9, p. 121) : I. Zone of Clonograptus flexilis and TetraA graptus j-Tetragraptus II. Zone of Tetragr. quadribrachiatus J beds III. Zone of Didymograptus a Subzone of D. nitidus, D. patulus lp.., h Subzone of D. extensus, Goniogr. ^ Didymograptus thureaui J IV. Zone of Didymograptus bifidus a Subzone of Goniogr. geometricus, Phyllogr. anna b Subzone of Didymogr. similis, Phyllogr. typus V. Zone of Diplograptus dentatus a Subzone of Climacogr. pungens, Didymogr. forcipi- formis b Subzone of Phyllogr. angustifolius, Retiogr. tentacu- latus c Subzone of Desmogr. and Trigonogr. ensiformis. Deepkill shale has been found in the Catskill quadrangle in five places. It is, however, undoubtedly present in more localities, or along all the Cambrian-Ordovician boundaries, but fails to be recog- nized by being infolded with the Normanskill beds or broken up into slices by the faulting. The five localities are a long strip, one and three-quarters miles long along the eastern foot of Mt Merino; another narrow strip in the section exposed in the road cut on the Greendale station to Greendale road ; a third a mile farther south, probably the continuation of the outcrop in the road cut, along the Schodack-Normanskill line, directly west of Blue hill; a fourth on the west side of the narrow southeastern finger of the Germantown inlier of Lower Cambrian rocks, beginning half a mile west of Bing- ham Mills (Baker Mills on older maps) and extending south for one and one-half miles, and finally a small outcrop on the southwest corner of the long middle finger of the Germantown inlier beginning a mile south-southeast of Viewmonte and traceable half a mile southward. The Deepkill shale is recognizable in all these localities by its 82 NEW YORK STATE MUSEUM lithologic characters, the alternations of greenish gray more or less siliceous limestone and black shale; the siliceous layers usually marked by numerous black worm trails and burrows. Fossils were found in the third and fifth outcrops that indicate the lower Deepkill horizons, viz. Didymograptus nitidus (Hall) in the third and Tetragraptus similis (Hall) in the fifth locality. The only larger fauna was obtained in the Ash Hill quarry hori- zon, extending from Ash Hill quarry near the south shore of South bay at Hudson along the east foot of Mt Merino to the southeast corner of the mountain, where it is separated from the Normanskill by a fault. The Ash Hill quarry exposure (see figure 29) and its fauna were described by Ruedemann (’04, p. 499-500), from whom we quote: Transitional subzone. The fortunate discovery of a Phyllograptus in the shales of the Ashhill quarry at Mt Merino near Hudson, by Prof. A. W. Grabau, has led to the finding there of a fauna which is a blending of the typical forms of the zone with Diplograptus dentatus with some species of the preceding zone. It, therefore, appears to happily fill, to a great extent, the gap in the continuity of the graptolite horizons, caused by the interruption of the outcrops between graptolite beds 5 and 6 of the Deep kill section (zones with Didymograptus bifidus and Diplograptus dentatus). The lithologic character of the beds at the Ashhill quarry is strik- ingly similar to that of the Deep kill beds, the bands of black grap- tolite shales being also intercalated in thicker masses of greenish, silicious shales. The Ash hill quarry has furnished the following forms : Dendrograptus sp r Ptilograptus plumosus Hall c Goniograptus perflexilis sp. nov. mut rr Tetragraptus quadribrachiatus Hall rr T. taraxacum sp. nov rr T. pygmaeus sp. nov r Didymograptus forcipiformis sp. nov c D. filiformis Tullberg r D. gracilis Tomquist r D. cuspidatus sp. nov rr D. spinosus sp. nov r Phyllograptus angustifolius Hall c Diplograptus dentatus Brong cc D. laxus sp. nov c Climacograptus pungens sp. nov cc Glossograptus hystrix sp. nov r Trigonograptus ensiformis Hall rr Retiograptus tentaculaUis Hall r While the typical species of the zone with Diplograptus dentatus prevail, both in number of species and individuals, thus characteriz- ing the beds as belonging to that zone, the congeries contains still a [83] Figure 29 Ash Hill quarry at northeast corner of Mt Merino. Shows chert and siliceous slate beds. (E. J. Stein photo, 1929) [84] GEOLOGY OF THE CATSKILL QUADRANGLE 85 goodly number of species met only in the deeper horizons at the Deep kill, namely, Goniograptus perflexilis, Tetragraptus taraxacum and T. pygmaeus, Didymograptus filiformis and D. gracilis. The Ash hill quarry beds represent hence a very early or initial phase of the zone with Diplograptus dentatus not met with at the Deep kill, but whose existence was surmised on account of the considerable break in the rock succession at that place. The Dendroidea which consti- tute so large a portion of the fauna of the horizon at the Deep kill are here represented only by a species of Ptilograptus and a few fragments of a Dendrograptus; but, as they also fail to be present in this zone in other countries, they may represent but a local element. A notable feature of this faunule is the considerable number of species not observed elsewhere, or in the preceding and succeeding horizons. Some of these forms, as Didymograptus cuspidatus and D. spinosus, represent moreover peculiar types and have no closely related congeners. Other species, as Diplograptus laxus and Climacograptus pungens, which are new and very rare in the Deep kill beds with Diplograptus dentatus, appear here in great profusion. These facts characterize the fauna as constituting a distinct subzone of the zone with Diplograptus dentatus. It is worth noting that since the Ash Hill fauna was described Didymograptus forcipiformis has also been found in the Deepkill fauna at the Deep kill associated with Didymograptus nitidus, Phyl- lograptus anna mut. ultimus and Climacograptus sp. nov., thus indi- cating the presence of the Ash Hill quarry horizon or a subhorizon, immediately preceding it, in the Deepkill section. In the Ash Hill quarry and above are exposed about 50 feet of alternating thin siliceous limestone bands and greenish gray hard siliceous slate with few very thin black shale bands with graptolites. The quarry has not been worked (for road metal) in many years and no graptolite layers are accessible at present. The beds form a westward overturned anticline, the principal body of the slate dipping east on both flanks. The new New York road south from Ash Hill quarry has opened various small outcrops of Deepkill shale. In one of them just below a farmhouse, a mile southwest of Ash Hill quarry, a characteristically rufous or rusty-brown weathering siliceous-calcareous slate contained : Climacograptus pungens Rued. Cryptograptus antennarius Hall Trigonograptus ensiformis Hall (large specimens) A rich graptolite bed was found at the southeast corner just before the end of the Deepkill strip (see figure 30), abutting there against the Normanskill chert. Here the formation consists of 86 NEW YORK STATE MUSEUM siliceous gray slate with few intercalated thin seams of black grap- tolitiferous slate, the slate grading into quartzite bands, followed by gray crystalline limestone beds, half an inch to an inch thick. These also carry on the bedding plane scattered graptolites and brachiopods. Some of the gritty beds have the bedding planes covered with small, round greenish mud-pebbles, giving them a conglomeratic appear- ance. These surfaces carry scattered specimens of Climacograptus pungens and Cryptograptus antennarius. The outcrop is especially marked by one bedding plane densely covered with Phyllograptus angustifolius Hall. The faunule con- sists of : Dendrograptus gracillimus nov. Didymograptus cuspidatus Rued. D. cf. nitidus (Hall) D. patulus (Hall) Tetragraptus quadribrachiatus (Hall) T. ( Etagraptus ) lavalensis Rued. Phyllograptus angustifolius (Hall) Cryptograptus antennarius (Hall) Chmacograptus pungens Rued. Diplograptus dentatus Brongniart Trigonograptus ensiformis (Hall) Glossograptus hystrix Rued. (brachiopod) A most interesting biotic element of this fauna was found in two small eurypterids : Dolichopterus antiquus Rued. Pterygotus (?) priscus Rued. Hitherto only one eurypterid Pterygotus deepkillensis (Rued.) was known from the Canadian system. These new forms must be counted therefore among the oldest eurypterids known, as the Cam- brian has afforded, with one exception, only types of Walcott’s order Limulava of the Merostomata. The composition of the graptolite faunule is distinctly the same as that of the Ash Hill quarry fauna and it is thus apparent that this horizon is strongly developed on the Catskill quadrangle; it would seem almost to the exclusion of the others, but in the intensely folded and faulted beds preservation at the surface is too much subjected to accidents to be a reliable indicator of the presence or absence of a formation. Furthermore, the outcrop of Ueepkill shale at the Stuyvesant rail- road cut, only ten miles farther north has afforded a small fauna, ap- parently comprising all the Deepkill horizons below the Ash Hill beds, so that a full series of the Deepkill shales* undoubtedly is present GEOLOGY OF THE CATSKILL QUADRANGLE 87 in this sector of the Hudson River valley below the Capital District. The Stuyvesant fauna comprises : Goniograptus thureaui (McCoy) postrtemus Rued. G. geometricus Rued. Phyllograptus angustifolius Hall Tetragraptus fruticosus (Hall) T. pendens Elies T. taraxacum Rued. T. quadribrachiatus (Hall) Didymograptus nit id us (Hall) D. patulus (Hall) D. bifidus (Hall) Besides these graptolites the brachiopods Lingula quebecensis Bil- lings, L. philo graptolitha Rued., and Orbiculoidea scutulum Rued, were collected at Stuyvesant. A very interesting feature of the Deepkill beds, as seen from Ash Hill quarry southward along the foot of Mt Merino, is that the hard siliceous slate becomes so fine-grained and compact that it assumes the character of dark green to gray chert. This character of the rock is already noticeable in Ash Hill quarry and still more distinctly at the south end of the belt (see figure 30) where typical chert ap- pears in the Deepkill section. It is still more interesting that these chert beds carry radiolarians exactly as the Normanskill chert beds do. Ruedemann and Wilson (’36) have described the following forms from the Deepkill chert: Ccnosphaera antique R. & W. Choenicosphaera multispinosa R. & W. Xiphosphaera parva R. & W. Acanthosphaera minuta R. & W. Heliosphaera venusta R. & W. Haliomma antiquum R. & W. Dorydictyum minutum R. & W. Doryplegma priscum R. & W. Spongotrochus primaevus R. & W. Many of these earlier Deepkill radiolarians are markedly smaller than the Normanskill forms. Apparently associated with the Phyllograptus angustifolius beds and practically adjoining it, are exposed two conglomerate beds of striking appearance along the Mt Merino road (see figure 45). These beds prove to be of much younger (Trenton) age than the adjoining Deepkill graptolite shale and of the character of the Ryse- dorph Hill conglomerate. They are in angular contact with the Deep- kill graptolite shale and separated by a fault plane from it. They will be described under the Rysedorph conglomerate (page 123). 88 NEW YORK STATE MUSEUM ORDOVICIAN SYSTEM Normanskill Formation The Normanskill formation, usually termed the Normanskill shale, consists of chert, grit and shale, the first predominating. The name “Normanskill shale” was used by Ruedemann in 1901 for beds typi- cally exposed at the Normanskill at the southern outskirts of Albany, at Kenwood. The petrographic character of the rocks (“Hudson shale, grit and chert”) was elaborately described by Dale (1899, 1904), the fauna fully listed by Ruedemann (1908, 1930). Dale (’99) in his table (facing p. 178) of Cambrian and Silurian formations of the slate belt of eastern New York and western Ver- mont, assigns to the Hudson grits 500-f- feet ; to the Hudson white beds 400 feet or less ; to the Hudson shales 50— (— feet ; to Hudson red and green shale 100— j— feet. We had an opportunity to make some estimates on the west side of Willard mountain on the Schuylerville quadrangle (Ruedemann, T4, p. 91 ), as follows : grit, 500d= feet ; white (chert) beds, 400± feet ; shale, 100± feet. This estimate is probably a minimum estimate and largely surpassed, for Ruedemann and Wilson (1936, p. 1542) estimated a total thickness of chert of about 600 feet on the southwest spur of Mt Rafinesque and found that the chert locality east of Fly summit, Washington county, measures about 400 feet. There were further found a hundred feet of black shale exposed on the lower Roeliff Jansen kill. These observations suggest greater thicknesses than had been conjectured before. Con- sidering the width of the Normanskill belt, attaining ten miles, with a further large portion buried under the Helderberg plateau on the west and the fact that only part of the shale is exposed, as owing to its incompetent character it is usually deeply eroded and buried by drift, it is probable that more shale is connected with the formation than appears on the surface. Dale (’04, p. 37) gave the following succession in descending order : 1 Black and gray shale with interbedded grit — Normanskill grap- tolite fauna 2 Similar shale with limestone and limestone conglomerate — Trenton fauna in limestone and cement of conglomerate 3 Black, siliceous, white-weathering, cherty-looking shale 4 Reddish, purplish, greenish shale with small quartzite bands The writer (T4, p. 89), mainly from the apparent synclinal struc- ture of Willard mountain on the Schuylerville quadrangle, came to GEOLOGY OF THE CATSKILL QUADRANGLE 89 the conclusion that more probably the grit was near the base. Also Dale remarked that he would have placed the grit at the base were it not for the fact that it is not always in contact with the Georgian, and the writer pointed out that the position of the grit in a western belt nearest to the younger Snake Hill shale and of the chert in the eastern belt nearer to the Cambrian on the Schuylerville quadrangle would indicate younger age for the grit. The apparent evidence of Willard mountain, however, was accepted as more weighty. The close study of the relationships of the chert in connection with the chert paper (1936) has afforded clear evidence of the older age of the chert and the younger age of the grit, although here again the structure of Mt Merino would suggest the opposite. In both cases the overturning of the syncline has produced a misleading appear- ance (see below page 146). The two belts, the western grit belt and the eastern chert belt are even more distinct and sharply separated on the Catskill quadrangle (see figure 35) than on those to the north. As the two divisions of the Normanskill formation are not only distinct in their lithologic character but to some extent (see page 115) also in their fauna, we will distinguish the two members as : Mt Merino chert and shale and Austin Glen grit and shale and describe them separately. The most important facts concerning the mutual relations of the two members are the eastern position of the chert belt, adjoining the Lower Cambrian belt, and the western position of the grit belt adjoining the Snake Hill formation, north and south of the Catskill quadrangle. Where the Deepkill shale is exposed, it is either in- folded with the Mt Merino beds as at Mt Merino or found in strips between the Mt Merino beds and the Schodack beds, as west of Blue hill on the iron ore ridge, or west of Bingham Mills and southeast of Viewmonte (see map). Another important clue is given by the presence of green and black chert pebbles in the arkosic layers of the grit, as at the Broomstreet quarry at Catskill. These pebbles leave no doubt of the presence of already consolidated chert in the sea when the grit was deposited. A third indication of the older age of the Mt Merino beds is given by the graptolite faunas, those of the Mt Merino beds containing the older elements, as N emagraptus gracilis, indicative of the lower Nor- manskill beds, while those of the Austin Glen beds do not carry these forms that have been recognized in the homotaxial beds of Great 90 NEW YORK STATE MUSEUM Britain as marking the older horizon. Future work will probably lead to the distinction of more refined horizons of graptolites in the Normanskill beds. It is true, the two belts are not always sharply separated and there appears a belt of chert in the grit belt south of Glasco and scattered small belts of grit in the chert belt, as west of Blue Stores. This has to be expected from the folded and thrust-faulted condition of the region. On the whole, however, the boundary between the two belts is distinct and where the two come close together as along the road south of Glasco the grit is found to be calcareous and fine- grained, thus indicating transitional conditions. The grit and chert are certainly nowhere interbedded on a large scale. a Mt Merino chert and shale. The Mt Merino chert was de- scribed by Dale as “white-weathering chert” of the “Hudson shales” and found by Ruedemann (1914) to be a most characteristic constitu- ent of the Normanskill formation. It has been fully described by Ruedemann and Wilson (1936) in all its lithologic, structural and faunal characters and the conclusion been reached there that for the larger part it is a deep-sea deposit formed in the abyssal depths of the bottom of the middle of the Appalachian geosyncline. This con- clusion (1936, p. 1563) is based on the presence of but small amounts of clastic material in the chert, the occurrence of the chert only with pure graptolite shales, the presence of fossil radiolarian genera, today characterized by deep-water habitat, and the presence of zones of radiolarite. This radiolarite, composed of chert and radiolarians, is compared with the radiolarian ooze found today only at depths of 12,000 feet, or greater. The silica content is believed to have been derived from volcanic activity in the Ordovician sea mainly to the north. The chert beds through their competent character to erosion form the backbone of the most prominent hills of the Normanskill belt, as notably Mt Merino and Blue hill. It seems that chert becomes especially prominent in anticlinal cross folds, a fact observed already by Mather (’43, p. 396) who wrote: They (chert outcrops) are generally situated on or near the trans- verse axes of disturbance, and at or near intersections of these northwest and southeast axes with the principal north-northeast and south-southwest axes of fracture and upheave. In these minor cases, as at the Van Wies point, it is possible that the cross fold has raised the chert beds to an especially high level, even through the grit beds and thus exposed them. The occurrence Figure 31 Green Normanskill chert from Glenmont. Photomicrograph (slide 2) showing dolomite rhombs precipitated with the silica. Crossed Nicols, x 20. (E. J. Stein photo) Figure 32 Deepkill chert from Stuyvesant Falls (slide 6), which is crystallized by metamorphism into fine-grained quartzite. Crossed Nicols, x 20. (E. J. Stein photo) [91] Figure 33 Normanskill red chert with radiolarians. From a point a mile west of Ghent (slide 50). Photomicrograph showing packing of Radiolaria to form radiolarite. Dark parts of section are hematite stain. Ordinary light, x 20. (E. J. Stein photo) Figure 34 Crushed brecciated radiolarite. From a point a mile west of Ghent (slide 51). Photomicro- graph showing large number of detached radiolarian spicules. Ordinary light, x 20. (E. I. Stein photo) [92] GEOLOGY OF THE CATSKILL QUADRANGLE 93 of chert, beds in cross folds may explain a few irregularities in the distribution of the chert and grit. There are numerous good outcrops of the Normanskill chert on the Catskil! quadrangle. The largest are upon and around Mt Merino and Blue hill. On Mt Merino the white- weathering chert is seen on top of the mountain, in the quarry on the north brow and especially well exposed along the New York road at the south end of Mt 94 NEW YORK STATE MUSEUM Merino (see figure 30) and still farther south towards the approach to the Rip Van Winkle bridge (see figure 54). Thickness of the exposed chert reaches here 40 feet. This chert belt reappears north of South bay at the west end of the city of Hudson where it forms the high cliffs along the railroad. Just north of the station one gets an excellent view of the massive chert beds from the train. On Blue hill the chert is associated with much red shale ; on the eastern foot of the mountain, just south of Greendale the chert is quarried for road metal. Twenty feet of solid chert are exposed here. It is considered as excellent road material for its hardness and known as “buckwheat” to the roadmasters. Fine exposures of chert are found south of Glasco along the road in road-metal pits and surrounding country, where 55 feet of heavy-bedded green chert and fine-grained thin-bedded calcareous grit are observable. The chert is here seen in one place to grade into greenish gray shale. Cliffs of white- weathering chert are also seen in the phyllite region at the eastern edge of the quadrangle three miles due east of Blue Stores and very fine ledges of white-weathering chert are exposed around Viewmonte. Along the road southeast of Germantown beds of white-weathering chert and shale were noticed which contain a two-foot bed of concre- tions of red chert. The petrography of the chert has been fully described by Ruede- mann and Wilson (’36, p. 1542), from whom we quote: The mineral constituents of the cherts, as determined by petro- graphic analysis, are few. Because of the somewhat metamorphosed condition of the rocks of the eastern New York shale belt, original composition is often masked by alteration products. However, certain pertinent facts stand out. In every section of chert studied, silica is the main constituent. With the exception of some material from Glenmont and the locality south of Glasco, truly amorphous silica is rare. Most of the chert is definitely cryptocrystalline. In some instances, for example, the Deepkill chert of Stuyvesant Falls, crystallization of chert, has pro- duced good quartzite. Ordinary light usually causes the radiolarians to appear in thin sections like windows in a darker wall (see figure 33). In some, ordinary light shows them stained by carbon. The black Normanskill chert of Stuyvesant Falls, which is interbedded with graptolitic shale, shows this feature. Under cross nicols, the fossils are seen to be minutely cryptocrystalline, suggesting that the originally chalcedonic silica of their tests, being purer, crystallized more readily than the silica of the matrix. Thin sections of chert from Mt Rafinesque, from a mile south of Becraft mountain, and from just north of Mt Tom, show mass polari- zation, extinction occurring parallel to and also at right angles to the GEOLOGY OF THE CATSKILL QUADRANGLE 95 bedding. This is probably the result of mineral parallelism, effected during crystallization and producing a foliation parallel to the original microscopic bedding. This is purely a pressure effect. Opaque material in some of the sections seems to be carbon, derived from organisms and strung out in small masses along the bedding. In other sections, it appears to be argillaceous material, probably representing original colloidal clay, the sericite needles in some of the darker chert probably representing original colloidal clay. . . . Chert from Mt Rafinesque exhibits a very little pyrite, which may be secondary. All of the Deepkill and much of the Normanskill chert contains dolomite rhombs up to two millimeters in length (see figure 31). The Deepkill is especially rich in carbonate, a fact that may assist in correlation, where fossils are absent. The red chert, or jasper, is rich in hematite in ultra-microscop- ically fine grains, irregularly disseminated throughout the siliceous matrix, producing a clouded appearance. In the chert, clastic material is extremely scarce but is found in thin beds as subangular quartz fragments. The fact that only chemical and colloidal precipitates make up the chert, whereas continent-derived material accounts for less than one per cent of the bulk, lends weight to the belief that the chert rep- resents a sediment of the deeper sea, more or less remote from any continental platform. Color The chert is of various colors. The Deepkill chert is everywhere gray-green and is commonly characterized by discontinuous black markings which may be worm trails. The Normanskill chert is found in associations of black and green, red and green, as well as black alone and green alone. The most common is green, although in Washington county, large thicknesses of red are associated with green. Black chert is found in great quantity at Stockport and at Van Wie’s point, in both places, somewhat argillaceous and carrying graptolites. Masses of red chert are found between Glasco and Kingston, between Ghent and Chatham Center, on Mt Rafinesque, and in Washington county in the slate belt. Several studies have brought out the fact that colloidal silica has the property of absorbing considerable quantities of other substances. Silica seems to have particular affinity, in this respect, for carbon. The thin sections show that, as a general rule, the black chert is actually green chert in which there is a considerable amount of ab- sorbed carbon. The blackest chert is that of the Stockport-Van Wie’s point type, which contains carbonized graptolite remains. Thus the color is probably due, in part, to carbon derived from organisms, absorbed by the colloidal hydrous silica. Some slides show radiolar- ians darkened by carbon so as to set them apart from the matrix. Although carbon has a darkening effect, much of the black color 96 NEW YORK STATE MUSEUM x of the chert is imparted by argillaceous material, which was probably originally colloidal and admixed syngenetically with the colloidal silica. It can be seen in the sections of banded black and green chert from Stuyvesant Falls and Chittenden Falls that the black is like the green except for larger amounts of opaque (carbon) material, strung out in lenses along bedding planes. Davis has shown that many, but not all, green and gray cherts are the result of discoloration of cherts originally red. Red cherts, where iron oxide is dissolved out by circulating water, become leached and of greenish color. Greenish cherts, therefore, often show residual cores of red chert. This conclusion of Davis is of considerable importance as in- dicating the original existence of much greater quantities of red chert than are now observed in the sections. There may have been much more radiolarite originally than is now indicated. The white-weathering property, which generally characterizes the Normanskill chert, was believed by Dale to be due to the kaoliniza- tion of “a fine feldspathic cement.” A study of the thin sections does not establish the presence of such a cement. At more than a hundred localities visited, it was found that only the surfaces of chert exposed to the light had become white. This phenomenon is true of both bedrock and loose blocks. Hence, it is possible that the whiteweathering of the chert is, in part, a bleaching or photochemical effect, if it is not merely the result of selective weathering, which produced a porous condition (as proven with a touch of the tongue when the specimens are dry). Smith has concluded that the white patina of the Kineo rhyolite is of similar origin, likewise the result of bleaching. In the August 21, 1936, issue of Science, Leon P. Smith, in an article on “The weathering of flint artifacts,” stated that “the more attractive jaspers are undoubtedly affected by actinic rays, but a loosening of their silicic binding material occasionally exceeds the bleaching.” The origin of chert has been much discussed and there is no doubt that it originates in various ways. The theories of the origin of chert fall into three groups: 1 Chert is a secondary replacement by silica, of some sediment not essentially siliceous. 2 Chert is a result of organic metabolism. 3 Chert is a true sediment, deposited on the sea floor. Dale (’99, p. 186) calls it “a siliceous and feldspathic slate,” formed probably from “a feldspathic mud, with quartz fragments, and muscovite scales.” Cushing and Ruedemann (1914) and later Ruedemann ( 1930) considered the chert to be indurated shale. This view had to be given up by Ruedemann and Wilson (1936, p, 1545) after a closer study of the stratigraphy, petrography and GEOLOGY OF THE CATSKILL QUADRANGLE 97 fauna of the chert, in favor of the primary origin of most of the chert. They give the following argument : Recently, it has become usual to infer the origin of a particular chert from the nature of its associates, notably the associated sedi- ments. The cherty shales and cherts present a series, ranging from shale through shaly chert to chert. Were this a gradual change from bed to bed, it would be reasonable to assume, as has previously been done, that the change is the result of a silicification or replacement of originally argillaceous material. However, field study shows that many beds of massive chert are separated by shale partings that exhibit no indication of silica replacement. Just east of Fly summit, Washington county, Wilson measured a 400-foot section of chert. Many of the beds are two feet thick and are separated by an eighth of an inch, or slightly thicker, black argillaceous shale beds. At the south end of Mt Merino, south of Hudson, there are four-inch and five-inch beds of solid chert, separated by as thick, or thicker, argillaceous strata. Similar outcrops are numerous. A true induration, where shale, which is characterized by thin bedding, is replaced by silica, would show the original bedding preserved in pseudomorphic detail. Actual observation, however, demonstrates that many of the chert beds show no thin banding within. It must be admitted, on the other hand, that many beds do show a fine, even microscopic, banding. Hence, if the unbanded beds can be accounted for, it might be argued that the banded beds are indurated shale. It is significant that thin sections of chert from Stuyvesant Falls show chert with intercalated thin bands of very fine-grained quartz, clearly in its original form, leaving no doubt that, in this case, both the quartz and the chert must be of syngenetic origin. At several localities just west of the Taconic range, the chert beds are cut by quartz veins in such a way that the quartz is clearly seen to be of a later generation. These same veins intersect beds of shale and chert alike, and the shale is not silicified. The locality at the south end of Mt Merino exhibits an intra- formational conglomerate or breccia, which is composed of frag- ments of chert and limestone in a calcareous matrix. This is re- peated in several beds, separated by shale and chert beds. It is evident that here the chert pebbles within the conglomerate are of original chert. Secondary replacement by silica can not be so selec- tive. A similar occurrence is to be found one and one-fourth miles north of Athens, on the west shore of the Hudson. At Troy, on the Rensselaer Polytechnic Institute campus, Ruede- mann found a fault breccia of post-Ordovician (Taconian orogeny) age, separating the Lower Cambrian and the Ordovician at the great thrust plane (“Logan’s Line”). This Poestenkill fault breccia is replete with fragments of Ordovician limestone (Bald mountain), grit (Normanskill) and black chert. There is no chert known from 98 NEW YORK STATE MUSEUM the Cambrian of the region ; hence, that of the breccia must be Ordo- vician, and essentially in its Ordovician lithologic condition. [We may add here also the occurrence of green and black chert pebbles in the Normanskill grit arkose at the Broomstreet quarry at Catskill mentioned before.] The presence of radiolarians in the chert is the best evidence that the chert is not secondary, as Paleozoic radiolarians are completely siliceous organisms and require silica for the construction of their tests. There must have been a sufficient amount of silica present when the radiolarians lived. Furthermore, radiolarians are rare in any except siliceous sedimentary rocks. This indicates that they are practically restricted to cherts and siliceous shales and that they have not simply drifted into siliceous deposits from elsewhere. Small amounts of chert in more or less isolated patches may be accounted for by the secretion of silica by organisms. Some cherts contain so many radiolarians that they are termed “radiolarites.” Sponge spicules are found in some chert, especially in the nodular variety. But all chert is not characterized by such fossils. Radiolarians are present in the Normanskill chert to a varying degree. It is impossible to ascertain their relative abundance from less than several thousand systematically collected rock specimens. However, it is apparent that, although some sections are replete with radiolarians, or nearly composed of them, others are completely barren. This condition is proof that the radiolarians are incidental and that the chert is not a result of their decomposition (PI. 3, fig. 1). The fact that 27 out of 51 chert slides showed radiolarians suggests that the latter may be found in all chert beds and that all this chert is of similar origin. Owing to the small amounts of silica in seawater, the view that thick chert beds were deposited as silica gel meets serious obstacles, as fully discussed by Davis, for, even though it is fully recognized that electrolytes tend to cause the coagulation of colloids, it is neces- sary to provide for the silica, which, for instance, is brought by rivers in greater quantities into the sea rich in strong electrolytes, some mechanism capable of concentrating it into definite areas of sedimen- tation. This difficulty has led many (among them, Davis) to the view that submarine volcanic exhalations or submarine springs producing magmatic water are necessary to explain the great deposits, hundreds of feet thick, as in the Franciscan group. This hypothesis seems well supported by the presence of volcanic rocks, both intrusive and extrusive, in connection with the more important chert deposits in many parts of the world. From a comparison of graptolite faunas, it appears that, during Normanskill time, there was marine connection between eastern New York, across Newfoundland, to the North Atlantic and Great Britain. All these sections of Normanskill age contain chert and Newfoundland together with New England and Great Britain have GEOLOGY OF THE CATSKILL QUADRANGLE 99 an associated igneous chapter in their histories. It is not impossible that the Canadian eruptives contributed such an excess of silica to the geosyncline in its northeast portion that the effects of it were reflected, farther south-southwest as deposits of chert. Ruedemann and Wilson found further that time is an important factor of deposition of the chert, deposition having probably taken place at a very slow rate. They arrived at the following conclusions : At Stuyvesant Falls, Columbia county, are two distinct sets of chert. One is composed of light-grayish rocks, whose textures range from cryptocrystalline or cherty to quartzitic. In fact, there are some beds that are hard to classify according to ordinary terms. They may be termed grainy cherts or fine-grained quartzites. These fine-grained quartzites are obviously derived from amorphous chert that was deposited by colloidal silica, but, owing to a slight or begin- ning metamorphosis, they have been altered into an extremely fine-grained quartzite, the angular grains of which fit closely to- gether. European authors have, for some time, recognized the fact of the metamorphism of amorphous chert into fine-grained quartzite. The other set of chert at Stuyvesant Falls is stratigraphically above the first and is composed of material quite different in appear- ance. Here, the chert forms beds up to six or eight inches in thick- ness, which, in turn, are composed of alternating black and dark green bands of exceedingly fine, crystalline material. These beds are separated by black graptolite shale. The alternation of chert and shale, both of which are composed of colloidal material, seems to indicate that long times of almost pure water were interrupted by epochs of relatively large and rapid supply of clay matter, at times either colloidal or detrital. The extremely fine microscopic bedding of some of the chert, with fine black organic films on the bedding planes, is proof that some of the chert was deposited slowly. Moore and Maynard have pointed out that silica is deposited at a slow rate by electrolytes and that time is, therefore, an important factor in the precipitation from dilute solutions. On the other hand, the amorphous chert from Glenmont (PI. 2, fig. 1) contains authigenic dolomite crystals, fairly evenly distributed in the chert and clearly syngenetic with the chert, thus leaving little doubt of the chemical precipitation of that chert, which, as bedding is not discernible, may have taken place more rapidly and from a more concentrated solution. From these facts, the writers conclude that the Deepkill and the Normanskill cherts represent consolidated, dehydrated marine deposits of colloidal silica (plus smaller amounts of other deposits). The silica was probably contributed to the sea, through submarine or continental volcanic activity, in particles of colloidal dimensions. The principal outcrops of the Mt Merino beds are at Mt Merino, south of Hudson. Here a road-metal pit on the north brow of the mountains since expanded into a large quarry on the land of the 100 NEW YORK STATE MUSEUM Reverend Claw was worked by the writer in 1901 and furnished the following fauna (see Ruedemann ’08, p. 13) : Thamnograptus capillaris (Emmons) Corynoides gracilis mut. perungulatus Rued. Didymograptus sagitticaulis (Hall) Gurley D. subtenuis (Hall) Azygograptus? simplex Rued. Leptograptus flaccidus mut. trenton- ensis Rued. id. var. spinifer mut. trifidus Rued. Nemagraptus gracilis (Hall) id. var. linearis Rued. id. cf. var. nitidulus (Lap worth) Dicellograptus gurleyi Lapworth D. sextans (Hall) id. var. exilis Elies and Wood. id. var. perexilis Rued. Dicranograptus nicholsoni var. par- vangulus Gurley D. ramosus (Hall) D. spinifer Elies and Wood, id. var. geniculatus Rued. Diplograptus ( Orthograptus ) incisus Lapworth D. acutus Lapworth D. angustifolius Hall D. ( Glyptograptus ) euglyphus Lap- worth Glossograptus ciliatus Emmons id. var. debilis Rued. G. whitfieldi (Hall) Cryptograptus tricornis (Carruthers) Climacograptus modestus Rued. C. scharenbergi Lapworth C. bicornis Hall Lasiograptus mucronatus (Hall) L. bimucronatus Nicholson This list contains half of the some 60 species of graptolites from the Normanskill beds of New York and it has since been enlarged by further collecting in the quarry which offers at present the best collecting ground for Normanskill graptolites in the State. Collec- tions at the place were made under Hall and the locality recorded under its old name of “Mt Moreno,” a name which has been super- seded by the more correct name Mt Merino. Also the brachiopods (see Ruedemann, ’34, p. 79 ff.) Paterula amii Schuchert, Leptobolus walcotti Ruedemann and Schisotreta papilliformis Ruedemann and the sponge Pyritonema rigidum Ruede- mann (Bui. 262, p. 37) have been described from the Normanskill shale at Mt Merino. P . rigidum consists of bundles of long straight rhabd-like bodies. Recent collecting by Clinton F. Kilfoyle has added a new sponge Teganium merino and a new graptolite Lasiograptus pusillus. There were altogether 13 graptolite localities found in the Mt Merino beds, as opposed to but two in the Austin Glen beds (to which are to be added several around Catskill found by Professor Chadwick). Among these may be mentioned the quarry to the south of the Greendale road beyond the cut which contains as the most common forms Dicellograptus sextans, Dicranograptus ramosus et al. and the shale east of the iron ridge at the next crossroad which has afforded Corynoides gracilis, Didymograptus sagitticaulis , Dicello- graptus exilis, as the prevailing types. In a road cut one and one- half miles southwest of Elizaville black shale associated with chert con- tained Didymograptus subtenuis, Climacograptus parvus, Crypto- graptus tricornis and Diplograptus ( Glyptograptus ) euglyphus. GEOLOGY OF THE CATSKILL QUADRANGLE 101 Another locality where graptolites occur in chert is in a road cut one and one-fourth miles west of the Twin ponds. It has afforded Corynoides gracilis, Didymograp tus subtenuis and C limacograptus caudatus. A small collection ( Diplograptus sp., Climacograptus par- vus etc.) was found in a quarry a mile west of Upper Red Hook. A whole series of graptolite localities were seen in the new road cut of the road from Burden to Livingston, though not any proved prolific. Corynoides sp., Didym ograp tus serratulus, D. sagitticaulis, C limac o grap tus parvus, C. eximius, Diplograptus angustifolius were found. Also the presence of infolded Deepkill was suggested by the appearance of some of the shale and the presence of Didymo- grap tus cf. filiformis and Phyllograptus cf. anna. An important biotic element of the Normanskill formation was discovered by Ruedernann and Wilson (’36) in the Radiolaria. These have been described in the Bulletin of the Geological Society of America cited above. The following species were reported from the Catskill quadrangle: Cenosphaera pachyderma Riist. — Glasco Stylostaurus hindei R. & W.- — Glasco (sole locality). Much larger faunas were found in the radiolarite from Fly sum- mit, Washington county, and from an outcrop a mile west of Ghent, Columbia county, and northeast of our quadrangle. Altogether 23 species of radiolarians were described from the chert of the Normans- kill formation, but there is no doubt that this is only a fraction of the radiolarian fauna that could be extracted from the chert by more extensive, systematic search. The bearing of this radiolarian fauna on the question of the origin of the chert has been fully discussed by Ruedernann and Wilson (1936, p. 1557). They concluded that the presence of radiolarite, a rock composed of chert and radiolarians (see figures 33 and 34), and the occurrence of radiolarian genera ( Staurosphaera , Haly- calyptra, Stylostaurus ) that today do not occur above 12,000 feet indicate, with the view that the radiolarite is to be correlated with the recent radiolarian ooze, a depth of formation for some of the chert of more, than 12,000 feet. This view is in agreement with the writer’s conclusions, arrived at in the study of the graptolites, that these comprise a plankton fauna of the open ocean (1934). A corollary of this conclusion is again that the Appalachian geosyncline formed at earlier Normanskill time a wide open sea of suboceanic dimensions (see page 180), at the bottom of which the Mt Merino chert was formed as syngenetic deposit probably under the influence of volcanic eruptions under some part of that sea. 102 NEW YORK STATE MUSEUM b Austin Glen member. The Austin Glen member of the Normanskill formation has been named from Austin Glen in the Catskill valley close to the village of Catskill. The grit with thin shale intercalations is here magnificently exposed in the bed of the creek (see figure 36). It forms a north-south striking anticline, giving an outcrop of 355 feet length across the strike and exposing beds of grit of various thickness, some 12 feet thick. The Manlius rests here back in the woods flat on top of the anticline. Another still more instructive outcrop is seen in the Broom Street quarry in South Catskill (see figure 37). Here a section of a broad syncline with a thrustplane in the middle has been uncovered showing grit beds from below upward with thicknesses of 35, 5, 27, 4, 20, 1 5— j— feet and thin shale intercalations, giving a most imposing view of the massiveness of the grit beds. In the upper left-hand corner of the quarry is seen an exposure of gray and black shale with inter- calated thin grit beds that is separated by a cross fault from the grit and has afforded a combined fauna of graptolites and eurypterids (see page 115). Most interesting features of this quarry are several arkosic conglomeratic beds composed of small mud pebbles, but also pebbles of black and green chert. The arkosic conglomerate contains besides the mud and chert pebbles large rounded quartz grains, some calcareous matrix in places and feldspar crystals (both monoclinic and triclinic), and small green bodies, probably hornblendic. There are red and brown streaks in the grit several inches thick composed of rounded grains of smoky and clear quartz and a clayey matrix with hematite and limonite. The aspect of these streaks is deceivingly like that of some of the Burden iron ore ; the iron content, however, is very small, amounting for the most part to no more than a staining of the clay (fide Newland). When traced laterally the conglomerate beds were found to form lenses two to three feet thick and 12 to 20 feet wide. A little farther north this arkosic conglomerate forms small lenses, a few inches long, that are scattered through the grit. These occurrences give the impression that the mud pebbles form- ing the conglomerate, were piled up by small eddies or crossing waves on the sandy bottom of the sea. Some of these pebble layers are found on the bedding planes (see figure 38), others are intra- formational (in one place 11 were counted in 10 feet of grit). Coarse ripple marks were observed years ago on the surface of one bed, with winnows of macerated eurypterids and seaweeds in the valleys of the ripple marks. [103] Figure 36 Top of anticline in Normanskill grit striking across Catskill creek in Austin glen, Catskill. The Manlius rests horizontally on the grit farther back in the woods. (E. J. Stein photo, 1936) [104] Figure 37 Heavy Normanskill grit beds. Large, downward concave thrust-plane crosses quarry. The shale containing graptolites and eurypterids is exposed in the upper left corner. Normal fault in background. Broome Street quarry, South Catskill. (E. J. Stein photo, 1936) Figure 38 Normanskill grit bedding plane with mud pebbles. Broom Street quarry, South Catskill. (E. J. Stein photo, 1936) [105] \m Figure 39 Alternating Normanskill grit and shale. Along New York Central Railroad, one mile south of Linlithgo. See also figure 42. Courtesy of New York Central Railroad. (Sharp photo, 1914) GEOLOGY OF THE CATSKILL QUADRANGLE 107 The crowded clay pebbles on the bedding plane, shown here in figure 38 may well be of the nature of “ Ton- Gallon, ” as the Germans call them: clay balls formed by the breaking up of thin clay-seams on the sandy tideflats, that are broken up by sun and wind and roll up. (Hantschel, ’36, p. 341). These ton-gallen occur already in Precambrian formations (v. Bubnoff, ’37, p. 37.) Larger mud pebbles, up to half a foot in diameter are often seen in the grit, as in a road-metal pit along the road north of Catskill. These mud pebbles appear to have been clay balls that rolled along with the current upon the sandy bottom, as one sees them today on the bottom of rivers or bays. Numerous outcrops, such as the fine sections of vertical beds along the New York Central from Hudson to the south end of the quad- rangle and beyond (see figure 39), show the regular, hundredfold repeated alternation of grit and shale. Owing to their competent character the thick grit beds with inter- calated shales that serve as gliding planes, form exquisite material for the orogenic forces. They bend, where pure shale is merely intensely crumpled, into fine upstanding or overturned folds. These are beautifully exhibited along the New York Central railroad (see figures 40 to 43). A fine overturned fold of grit and shale is also seen on the north side of the Catskill creek in Catskill (see figure 44). A striking exposure of Austin Glen grit and shale is found just north of Tivoli station in an abandoned quarry. Here more than 100 feet of shale and grit are exposed, the grit beds ranging from one foot to 10 feet in thickness. As in other exposures along the railroad on steeply dipping rocks the underside of the grit beds is often marked by mud flow structure, indicating the action of cur- rents and eddies. At the mouth of the Roeliff Jansen kill at Linlithgo even 100 feet of solid grit are visible. These and other exposures prove clearly that the Austin Glen member is an exceptional mass of grits and shales that reaches 500-f- feet in thickness. The grits, owing to their hardness, massiveness and resistance to erosion, appear in protruding ledges on the surface, while the equally thick masses of shales are buried in valleys and under drift and are shown only in exceptional cases, where river erosion has bared them, as in the Roeliff Jansen kill west of Burden where over 100 feet of black shales are exposed. Owing to the great thickness of the member it forms a broad belt about five miles wide at the widest part near the southern margin 108 NEW YORK STATE MUSEUM of the quadrangle. As a glance at the southern margin of the Capital District map (1930) will show, however, part of the belt is buried under the Helderberg plateau. The largest area of exposed Austin Glen grits is on the east side of the river, in Germantown, where many outcrops are seen along the New York road and from Cheviot to Tivoli and Madalin. The grit appears here in a multitude of ridges and ledges, south of Madalin in beds more than 30 feet thick! Black mud pebbles and cross-bedding are here observable in weathered ledges. The infinitely alternating beds of grit and shale, the lenses of mud pebbles, the cross-bedding, the large mud balls and the mud flow structure altogether give the impression that this formation was deposited in shallow water, probably near shore, where the velocity of the currents was frequently and rapidly changing, the slow currents depositing black and gray mud, the faster ones sandstone and grit. The petrographic character of the Austin Glen grit, as described by Dale (’99, p. 187) agrees with the macroscopic characters given above, all pointing to an abundance of partly fresh material brought to the sea from the weathered surface of near-by land. Dale gives the following description : It is coarse, grayish, sandy looking. Fresh fracture surfaces are very dark and show glistening glassy quartz grains and very fre- quently minute, pale, greenish, slaty particles. Under the microscope it consists of angular grains of quartz, orthoclase, plagioclase, and scales of muscovite, probably clastic. The cement contains not a little carbonaceous matter, secondary calcite and pyrite. . . . The marked features are the heterogeneity of the fragments, their irregu- lar size, angular outline, and usually the absence of any arrangement in them. A further peculiarity of the Hudson grits is that they contain particles of various fragmental rocks, showing that they were derived from the erosion not only of older granites and gneisses, but of sedimentary rocks of Ordovician or pre-Ordovician age; [the par- ticles of clastic rocks were found to consist] of shale, micaeous quartzite, calcareous quartzite, limestone or dolomite, shale and flint- The most abundant were found to be quartzite, slate and shale. Animals are not likely to flourish on bottoms of moving sand, often overwhelmed by inflows of mud. Fossils are therefore exceed- ingly rare in the Austin Glen beds. They consist of seaweeds, grap- tolites and eurypterids. The seaweeds occur as black irregular thick carbonaceous patches. They were originally described as sponges (Rhomb odicty on) by Whitfield (1886), but later recognized as plant remains (Clarke and Ruedemann 1912, p. 412). [109] igure 40 Crest of overturned pitching anticline in Normanskill grit and shale. One surface shows ripple marks. I hree-fourths of mile below Rhineclift along New York Central Railroad. Courtesy of New York Central Railroad. (Sharp photo, 1914) 1110] Figure 41 Syncline with fault on right cutting off anticline, and anticline on left. In Normanskill shale and grit. Along New York Central Railroad, south of North Germantown. Courtesy of New York Central Railroad. 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