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Vy : : Vey n Wis Cue = df’ tty 4g -* 7 ad Ahh LA) \ i ¥ | v Whe. e tou dd WS dd fied JvJV Wvrgtoviie Wy Vebiw.. d 440 phere ey ! nel WN vdvdeyd ved 9 a wiited ny ie4 y's Av db ddd edd yee due valid Hddth : . vo ewe , ~~ . aibeak be 4 Ve "wer aw “Cnn. we f rr 1 it . | ros —— [oo Oma — | San ~ od | 7 “er be oe ah "University of the State of New York Bulletin, ey : ape = second-class matter pias 2 eke w ga — Office at Albany, N. Y., under the Published fortnightly ee No. 561 . ALBANY, N. Y. FEBRUARY I5, 1914 New York State Museum JoHN M.. CLARKE, Director Museum Bulletin 170. GEOLOGY OF THE NORTH CREEK QUADRANGLE, WARREN COUNTY, NEW YORK BY WILLIAM J. MILLER PAGE PAGE ETUC id, be ws ew Sek ws ee 5 | Glacial and postglacial geology. ... 65 General topography and geology... 6 | Summary of geological history..... 76 Rocks of the region............. 8 | Economic geology ............... 78 mreuetural features, ....)...-.... as |< Tees oaks cites ol ee Yaw 87 ‘Topography. Re Ce See dia-s 3 wuteOs : ALBANY : THE UNIVERSITY OF THE STATE OF NEW YORK 1914 ; M36r-Mr13-1500 opened of the Coiversity Ay: (March 15s 1914) _ With years when terms expire é me ve toy St CLAIR McKztway M.A. bie: D.C.L. i eee IQr4 3 ee T. SEXTON oe B. LL. D. Vice Chancellor Pala 915 ALBERT VANDER VEER M.D. M.A. Ph.D. LL.D. Alba 922 Chester S. Lorp M.A, LL.D. - —- : 1918 Wituiam Nottincuam M.A. Ph.D Lip 1921 Francis M. CaRPENTER — - - - - 1923 ABRAM I. Erxus LL.B. aye 1924 ADELBERT Moor -—- - - = > 1925 CHARLES B. ALEXANDER M. ni oe B.LL.D. ‘Lit. D. Tuxedo Be yoax Mode: — = = = = = = = = 1920 ANDREW J. SHrpman M.A. LL.B. LL.D. 1916 Water G. KELLoce | President of the University and Commissioner of Education Joun H. Fintey M.A. LL.D. ’ Assistant Comawicctenere Baars S, Downinc M.A. L.H.D. LL.D. Far Higie E j on CuarLes F. WHEELOCK B. 5. LL.D. For Secondary Educati | Tuomas E. Finecan M.A. Pd. D. LL.D..For Elemeniary Ea a - Director of State LWerary iG I. WYER, Jr, M.LS. Directo; of Science and State Museum ‘Joun M. CLarKkE Ph.D._D.Sc. LL.D. . Chiefs of Divisions . _ Administration, GEORGE M. WiLtey M tg Bea teendance, JAMEs ‘D. SULLIVAN, _ Educational Extension, Wittiam R. Warson 8: _ Examinations, Hartan H. Horner B.A. History, James A. HoLpeEn B.A. _ Inspections, Frank H. Woop M.A. _ Law, Frank B. Givpert B.A.. ; . ; Library School, FRanK K. Water M.A. MLL. S. bs Public Records, THomas C. Quinn is ae Libraries, SHERMAN Wiziams Pd.D. New York State Education Department Science Division, March 12, 1913 Hon. Andrew. S. Draper LL.D. Commissioner of Education Sir: I have the honor to transmit herewith a manuscript entitled Geology of the North Creek Quadrangle, Warren County, New York, which has been prepared by Dr William J. Miller, a member of the temporary staff of this Division. Accompanyiing the manu- script are the necessary maps for its adequate illustration. I recommend the publication of this manuscript as a bulletin of the State Museum. Very respectfully Joun M. CLARKE Director STATE OF NEW YORK EDUCATION DEPARTMENT COM MISSIONER’S ROOM Approved for publication this 18th day of March 10913 Commissioner of Education University of the State of New York Bulletin Entered as second-class matter August 2, 1913, at the Post Office at Albany, N. Y., under the Act of August 24, 1912 Published fortnightly No. 561 ALBANY, N. Y. FEBRUARY I5, I914 New York State Museum JouHn M. Ciarker, Director Museum Bulletin 170 GEOLOGY OF THE NORTH CREEK QUADRANGLE, ’ WARREN COUNTY, NEW YORK BY at en, i ine tit, 2, > WILLIAM J. MILLER INTRODUCTION The North Creek quadrangle comprises an are j 215 square miles in the southeastern Adirondacks. The map! covers one-sixteenth of a square degree which lies’ wholly within Warren county. A branch of the Delaware and Hudson Railroad from Saratoga Springs passes through the region from southeast to northwest, with a terminus at North Creek village. This railroad is an important entry into the southeastern Adiron- dacks, especially for summer tourists. The principal villages of the quadrangle are North Creek, Hori- con, Pottersville, Chestertown, Wevertown, and Johnsburg with Warrensburg very close to the southeastern corner. Considered as a region so distinctly within the Adirondack Precambric rock area, it is unusally thickly settled and well supplied with roads, which have been a great help in making a detailed study of the complicated geologic features of the quadrangle. Agriculture is the principal industry, though during the summer months a large number of visitors come to the numerous hotels and summer board- ing places, especially those in the larger villages and around the lakes. This region, like the Adirondacks in general, was formerly heavily forested but the first growth timber has largely been cut off so that the lumbering industry is now nothing like that of earlier years. 1See map in pocket of back cover of this bulletin. 6 NEW YORK STATE MUSEUM GENERAL TOPOGRAPHY AND, GEOLOGS# As compared with the general Adirondack area, the North Creek quadrangle presents a rather unique assemblage of topographic forms. Long, prominent mountain ridges, usually with northeast- southwest trend, which are so common in the eastern Adirondacks, are practically absent from the quadrangle, and instead the domi- nant topography form is the separate, rounded mountain mass or dome which stands out conspicuously above the surrounding country. Such domes, which are numerous and widespread especially in the southern two-thirds of the region, are commonly from 500 to Soo feet high. The highest and largest of these domes is Crane mountain which rises 2000 feet above the immediately surrounding country. Among the other more notable examples are Hackensack,’ Moon, Potter, No. 9, Little, Huckleberry, Kelm, Chase, Prospect, Mill, and Stockton mountains. These domes always form striking features of the landscape. Ridges do occur but they are seldom more than two or three miles long and do not assume their usual importance in Adirondack topography. This peculiar North Creek topography has largely been produced by a very irreg- ular system of numerous faults in combination with a rather wide- spread though “ patchy ” distribution of comparatively weak Gren- ville strata. In the succeeding pages these matters are described in detail. The maximum range in elevation is from about 640 feet, where the Hudson river leaves the quadrangle, to 3254 feet at the summit of Crane mountain. Many of the mountain tops show altitudes ranging from 1200 to 2000 feet. The Hudson river, which is the largest stream in the south- eastern Adirondacks, passes through the midst of the quadrangle from the northwest to the southeast. The Schroon river, which is one of the chief tributaries of the upper Hudson, cuts across the northeastern portion of the area and thence along the western side of the adjoining Bolton sheet to reenter the North Creek sheet at the extreme southeastern corner near Warrensburg. It is worthy — of note that the Schroon river, in the northern portion of the area, flows at a level 200 feet below that of the Hudson to which it is tributary. All the drainage of the quadrangle passes into the Hudson, though that of fully two-thirds of the region does so by first entering the Schroon river. Within the map limits, scarcely a stream of any consequence enters the Hudson from the east, while several streams of considerable size, such as Patterson brook, Glen brook, and Mill creek, enter it from the west. ~ 10On the map the name of this mountain is misspelled. GEOLOGY OF THE NORTH CREEK QUADRANGLE 7 Quite typical Adirondack lakes and ponds are fairly abundant, about thirty of them being represented on the map. The largest is Schroon lake, only the southern end of which lies within the map limits. The others range in size from small ponds to lakes two or three miles long such as Friends and Loon lakes. From the geologic standpoint, the North Creek quadrangle is of more than the usual interest because of both the rock types and structures. With the single exception of the anorthosite, all the important rock formations of the eastern Adirondacks are abun- dantly represented. Except for the superficial glacial and recent deposits, the rocks of the quadrangle are all of Precambric age, and nearly all are highly metamorphosed, foliated, and folded. Following is a list of all the rock formations, except the Pleisto- cene, given in the regular geological order of relative ages: 5 Diabase: wholly nonmetamorphosed, occurring in comparatively small, narrow dikes, and clearly cutting all the other rocks of the region. 4 Pegmatite: wholly nonmetamorphosed, dikelike masses cutting all rocks except the diabase. 3 Gabbro: more or less metamorphosed, occurring in stocks or dikes and cutting all types of the syenite-granite and Gren- ville series. 2 Syenite-granite group: distinctly gneissoid rocks, representing several facies of a single great intrusive mass, and clearly younger than the Grenville. 1 Grenville series: highly metamorphosed and foliated sedimentary rocks, including crystalline limestone, quartzite, and various dark to light colored gneisses. These are the oldest rocks of the region. In spite of the rugged character of the topography, the accessi- bility of all parts of the quadrangle and the general excellence of rock exposures have afforded an unusual opportunity for detailed field work. Many important geologic relationships are very clearly exhibited. Following are the principal papers which have a more or less direct bearing upon the geology of the quadrangle: 1842 Emmons. Geology of the Second District, N. Y. 18907 Kemp & Newland. Preliminary Report on the Geology of Washington, Warren and Parts of Essex and Hamilton Counties. In 17th Annual Rep’t N. Y. State Geologist. 8 NEW YORK STATE MUSEUM 18908 Kemp, Newland & Hill. Preliminary Report on the Geology of Hamil- ton, Warren, and Washington Counties. In 18th Annual Rep’t N. Y. State Geologist. ne 18cqg Kemp & Hill. Preliminary Report on the Pre-Cambrian Formations in Parts of Warren, Saratoga, Fulton, and Montgomery Counties. In 19th Annual Rep’t N. Y.. State Geologist. rol Miller, W. J. Exfoliation Domes in Warren County, N. Yo tah State Mus. Bul. 149, p. 187-94. I9oil Miller, W. J. Pre-Glacial Course of the Upper Hudson River, In Bul. Geol. Soc. Amer., 22: 177-86. ROCKS OF CHE REGION GRENVILLE SERIES General statements. The Grenville series comprises the oldest known rocks of the area. They consist of a great mass of highly metamorphosed and crystallized sediments such as original lime- stones, sandstones, and shales which have been changed to crystal- line limestone or marble, quartzite, and various gneisses. Since it has not yet been definitely determined whether these rocks should be classed as Archeozoic or Proterozoic in age, the noncommittal term “ Precambric”’ is employed. The- weight of evidence is on the side of their Archeozoic age and it is certain that they can not be of late Proterozoic age. Among the proofs for the sedimentary origin of these rocks within the quadrangle are: (1) the very character of much of the material such as limestone and quartzite which can not possibly have been of igneous origin; (2) the arrangement of the rocks in distinct beds of widely different composition and often sharply al- ternating; and (3) the common occurrence of graphite (crystal- lized carbon) as flakes scattered through much of the rock, such graphite being almost certainly of organic origin. Grenville strata are known to be of common occurrence through- out the Adirondack mountain region and this, together with the facts that the total thickness of these strata is very great and that they extend over not only the Adirondack area but also a vast ex- tent of Canada, make it certain that those very ancient strata are of marine origin. It is evident that the Grenville sediments were laid down upon an ocean floor of even greater age but, in spite of twenty years of painstaking field work by several investigators, no trace of that ancient floor has certainly been recognized. Nor has any trace of that very ancient land, whose wearing down by erosion furnished the Grenville sediments, been found. It seems probable that those GEOLOGY OF THE NORTH CREEK QUADRANGLE Qg Pregrenville masses were either engulfed by the later great in- trusions or that they were changed beyond recognition. Areal distribution of the Grenville. About four-ninths of the surface rock of the quadrangle is Grenville, provided we include the Grenville which makes up considerable portions gf the areas of mixed gneisses. It should be noted that the Grenville here as- sumes much more prominence than is usually the case in the Adi- rondacks. Also, as the accompanying map shows, the Grenville is very widespread in its distribution, it being least prominently developed in the central and northern portions. A striking feature is the “ patchy” character of its distribution, this being due to the very irregular manner in which the great igneous intrusions broke through and cut to pieces the Grenville strata. The three types of Grenville which are sufficiently different to allow of separate representation on the geologic map are: 1 Crystalline limestone which is generally associated with dark hornblende gneiss, this latter rock often being garnetiferous. 2 Quartzite in thin to thick beds and usually more or less inter- bedded with thin layers of biotite gneiss or sometimes a little limestone. 3 Other gneisses, chiefly gray feldspar-garnet or dark gray biotite- garnet-feldspar or white feldspar-gneiss. Occasionally a little limestone, quartzite, or hornblende-gneiss may occur closely associated, especially where the glacial drift is heavy. The largest area of Grenville occupies the western portion of the quadrangle and by far the greater part of it consists of lime- stone and its associated hornblende gneisses. A considerable area of quartzite lies south of Sodom and a smaller one east of Little mountain. The only distinct area of mica-feldspar gneiss covers a few square miles south of Thurman. Toward the southeast occur two irregular shaped areas of Gren- ville which are almost entirely made up of limestone and associated hornblende-garnet gneiss, the limestone being especially thick and well shown in outcrops just west of the Potter-Birch mountain ridge. The large and very irregular shaped area along the eastern side of the sheet consists mostly of various gneisses with one consider- able area of quartzite south of Pottersville and another east of Chase mountain. The only mappable limestone belt there is a small one extending eastward from Valentine pond. 10 NEW YORK STATE MUSEUM A patch of Grenville gneiss lies at the extreme northwestern corner of the sheet and another at the northeastern corner, while a belt of limestone just enters the northern map limit at the Nat- ural Bridge. The Grenville around Loon lake consists mostly of white to gray gneisses. A number of small patches of Grenville are shown within the igneous rock areas and these usually represent actual inclusions of the Grenville which are large enough to be indicated on the map. No attempt has been made to show the many smaller in- _ clusions. The Grenville occurring within the areas of mixed gneisses will be discussed in connection with those gneisses. Grenville types. The Grenville types are described in consid- erable detail because, in the writer’s opinion, if the broader struc- tural and stratigraphic relations of the Grenville series are ever to be worked out, it is necessary to have these rocks carefully descriped and mapped over a much larger area than that of a single quadrangle. When a number of the other quadrangles of the south- eastern Adirondacks, in addition to those of Broadalbin, Saratoga, and North Creek already published and the Lake Pleasant now being studied, are mapped in detail, it is quite possible that some of the larger structural and stratigraphic features may be made out. Crystalline limestone. In common with the Newcomb and the southern portion of the Schroon lake sheets, the limestone of the North Creek sheet is much more prominently developed than is usual in the southeastern Adirondacks. The numerous outcrops of limestone (actually observed) are indicated on the accompany- ing map. Perhaps the most abundant variety is a nearly white, medium to coarse crystalline, very calcitic limestone through which are scat- tered numerous flakes of graphite and phlogopite or biotite and occasional specks of pyrrhotite. The calcite crystals range from a few millimeters to more than a half inch across, while the graph- ite flakes are commonly several millimeters across. Other crystals less often seen in this rock are pyrite, nearly colorless pyroxene, and brown tourmaline. Rarely the limestone is rather dolomitic. This variety of limestone appears in many excellent exposures, the most extensive outcrops perhaps being on the small hill just south of Daggett pond. A second very common variety is nearly white, medium to coarse-grained calcitic and with numerous irregular shaped, pel- lucid quartz grains, flakes of graphite, and specks of pyrite or Plate 1 — mae Rag >> . ; ~ : Courtesy Moore & Gibson Co., New York View of the Natural Bridge on Trout brook, 2 miles northwest of Pottersville. During the season of low water all the water flows under the arch here shown. . The rock is banded, Grenville, crystalline limestone. GEOLOGY. OF THE NORTH CREEK QUADRANGLE | II pyrrhotite scattered through the mass. The quartz grains usually range in size up to five or six millimeters and stand out as pale straw yellow or clear masses in very bold relief upon the weath- ered surfaces. Tiny garnet and green pyroxene crystals are rarely present. This variety is also widely distributed and among many _ other good outcrops are: just east of North Creek; at the Natural Bridge; just south of Crane mountain; and 1% miles due north of Warrensburg. A third variety which is rather widely distributed though not so common as those above described may be called serpentine lime- stone or green marble. One kind of this rock is medium-grained, nearly white, crystalline limestone but with many large blotches or irregular streaks of dark to light olive green serpentine scattered through it. A second kind has s¢attered through it numerous specks of serpentine or small pale green serpentinized pyroxenes. Different names have been applied to this green marble which has been briefly described by G. P. Merrill who says’: ‘‘ The serpen- tine in the Warren county Ophiolite, Ophicalcite or Verdantique as it has been variously called, is an alteration or metasomatic product after a mineral of the pyroxene group. The original rock would appear to have been simply a pyroxenic limestone, the py- roxene occurring either in scattering granules or in granular aggre- gates of considerable size.” Among other places this green marble is well shown in the quarries one-half of a mile southwest and three-fourths of a mile southeast of Thurman village, and in the prospect hole at the western base of Hackensack mountain. Pure white tremolite crystals are sometimes closely associated with the limestone as 1 many outcrops about a mile east of Little mountain pond. One and. one-half miles due north of. Warrens- burg irregular streaks or veins of tremolite, quartz, pyroxene, and titanite are closely involved with the limestone. The tremolite crystals are up to two inches long and the green pyroxenes up to one-quarter of an inch and perfectly formed. Asbestos veins sometimes occur in the serpentine marble, these being best shown at the asbestos mine three-quarters of a mile southeast of Thurman where numerous veins attain a width up to three-quarters of an inch. Green pyroxene or rusty biotite gneisses are sometimes involved in the contorted limestone in the form of streaks or inclusions which have been drawn out or broken by the pressure. See figure g and plate 12. 1 Amer. Jour. Sci., Mar. 1880, p. 191. 12 NEW YORK STATE MUSEUM A hand specimen, from the prospect hole 2%4 miles south of Pottersville, is a very coarse-grained mass of calcite, brown horn- blende, and graphite through which are scattered small flakes or crystals of phlogopite, pyrite, and pyroxene (mostly serpentin- ized). The hornblende and calcite crystals are as much as an inch across. Quartzite. In the quartzite areas shown on the map south of Sodom, south of Pottersville, and east of Chase mountain, the rock consists almost wholly of distinctly bedded, pure quartzite (with layers up to 14 feet thick) interstratified with thin layers of biotite-quartz gneiss. The quartzite of the area southwest of Thurman contains many closely involved tremolite and limestone beds. | Thin layers of quartzite are occasionally present in the other © Grenville areas but these are usually rather impure containing more or less feldspar, biotite, muscovite or graphite. | Hornblende-garnet-feldspar gneisses. Of the two principal facies of these gneisses, one is a gray, medium to fairly coarse- grained hornblende-feldspar gneiss in which are embedded occa- sional large brownish red garnets of the almandite type. The felds- pars comprise both orthoclase and plagioclase and the hornblende is very dark green to nearly black. Buiotite, magnetite, and pyrite generally occur in small amounts. The garnets never show crystal form but are always more or less rounded and highly fractured. These garnets commonly range in size from one to five inches and are often surrounded by rims or envelops of pure hornblende crystals. Fine specimens of such garnets, surrounded by rims of hornblende and embedded in the gray matrix, may be obtained at the old garnet mines near the top of Oven mountain and south of Holcombville. Another facies is fine to medium-grained, darker gray (with reddish tinge), less feldspathic, and more garnetiferous but with the reddish brown garnets all very small and rather evenly scat- tered through the rock. Small amounts of magnetite, quartz, and pyrite are also usually present. These hornblende-garnet-feldspar gneisses are almost invariably closely associated with the limestone beds, the two rocks often appearing in a single outcrop. Numerous fine exposures may be seen along the south and west sides of Crane mountain, 1 mile west of Pine mountain, just northwest of No. 9g mountain, and I mile east of Cherry ridge. Plate 2 W. J. Miller, photo Grenville light gray, very quartzose gneiss, as seen in the quarry near the southeastern end of Loon lake. The banded and jointed character of the rock is well shown. GEOLOGY OF THE NORTH CREEK QUADRANGLE 13 Feldspar-biotite-garnet gneisses There are a number of rather distinct facies of these gneisses which show all sorts of gradations from one to another. One common facies is a fine to medium- grained gneiss in dark gray and nearly white alternating bands. The biotite is wholly confined to the dark layers, while small scat- tering garnets appear in both. Such rock is common in the gneiss areas, being especially abundant on the mountain side east and south of Valentine pond and northeast of Fuller pond. Another facies 1s medium to coarse-grained and not so _ per- fectly banded. It is best shown in the small mountain 1% miles north of Valentine pond. A third facies is a fine to rather coarse-grained, gray to dark gray rock, clearly gneissoid, usually banded and with numerous pink to amethyst garnets up to five millimeters across. Such rocks are very common in the Grenville gneiss areas as, for example, in the quarry near the southeastern end of Loon lake and at the west- ern base of Prospect mountain. Hornblende-feldspar gneiss. The most common facies of these rocks is a fine to medium-grained, dark gray gneiss almost wholly devoid of garnets. It is very gneissoid and amphibolite-like but not at all banded. It is closely associated with limestone, some- times with thin layers of that rock interbedded. The whole ridge extending for five miles southeastward from North Creek is prac- tically made up of this rock. Another but similar looking gneiss contains orthoclase, plagi- oclase, hornblende, and hypersthene «together with small amounts of magnetite and graphite. This is a much more locally developed gneiss as, for example, immediately under the limestone at the Nat- ural Bridge. Feldspar-quartz gneisses. These are the white or very light gray gneisses of the district. Perhaps the most typical examples are found in excellent exposures along the road near the quarry at the southeastern end of Loon lake. This is a fine to medium grained, very light gray gneiss with some tiny biotite flakes and small brown garnets scattered through the mass. A slide shows about 80 per cent of orthoclase, microcline, and microperthite in nearly equal amounts; 13 per cent quartz; together with small amounts of plagioclase, biotite and garnet. This light gneiss is in thin to thick beds and repeatedly interbedded with biotite-garnet gneisses. A very similar light gneiss, but with graphite flakes, occurs a mile farther northward along the same road. I4 NEW YORK STATE MUSEUM Feldspar-quartz light gneisses also occur three-quarters of a mile south of Thurman; at Starbuckville; and one-quarter of a mile north of Chestertown. Pyroxene gneisses. These gneisses are much less abundant than © those above described. The most common facies is a fine to me- dium-grained intimate mixture of small grains or crystals of green pyroxene and reddish brown garnet, with sometimes one and some- times the other predominating. Such rocks are well exposed in the Sanders Brothers mine near the mouth of Mull creek, and at the old Parker mine just southwest of Daggett pond. Another facies is a greenish gray to greenish gneiss which con- tains more or less feldspar in addition to the small garnets. Such rock makes up the inclusion 1 mile west of The Glen, and also occurs along the road one-quarter of a mile north of the north end of Loon lake. Interbedded with the rock at this last named locality is a schistose orthoclase, green pyroxene, phlogopite rock, with occasional graphite flakes up to 3 or 4 millimeters across. Sillimanite-feldspar-garnet gneisses. Such rocks were observed at but two localities, namely, three-quarters of a mile west-north- west of Starbuckville and 1 mile south of South Horicon. A thin section and specimen from the large outcrop at the latter place shows the rock to be fairly coarse-grained, gray, moderately gneissoid and made up of a matrix of orthoclase, microperthite, and quartz in which are embedded many pale pink garnets, small prisms of sillimanite, tiny graphite flakes, and some small magnetite and colorless pyroxene crystals. At the first named locality the rock is well banded and contains fibrous sillimanite in irregular streaks and also some biotite. Graphite schists or gneisses. As we have learned, graphite fates are common in the limestone and sometimes present in the quartz- ites and various gneisses. True graphite schists or gneisses are, however, rare, the only ones noted being at the old graphite mine 1 mile southwest of Johnsburg where the rocks are light to dark. gray and thin to thick bedded. One specimen is almost a quartzite, but with numerous small biotite and graphite flakes. Another specimen is a feldspar-quartz schistose rock without biotite and fairly filled with graphite flakes generally from 1 to 2 millimeters across. Still another specimen is a feldspar-quartz-biotite gneiss with few graphite flakes. | Grenville stratigraphy. Any attempt to work out the strati- graphy of the Grenville series must of necessity be much more = GEOLOGY OF THE NORTH CREEK QUADRANGLE 15 unsatisfactory than if we were dealing with a great thickness of unaltered fossiliferous strata. However, because of the excellence and frequency of the exposures in most of the Grenville areas, some unusually good results have been obtained though it should not be understood that the statements or conclusions here given are always regarded as thoroughly established. Much detailed work on the adjoining areas will have to be carried on before such statements can possibly be made. So far as can be made out from a study of all the Grenville sections, the order of succession of the strata appears to be: 5 Dark gray biotite-garnet gneiss. Thickness unknown. 4 Dark hornblende gneiss. Thickness at least 2000 feet. 3 Crystalline limestone. Thickness of some 10,000 or 12,000 feet, but frequently interbedded with more or less hornblende or pyroxene gneisses or quartzite. 2 Quartzite. Thickness of about 3000 feet and generally pure except for very thin layers of biotite gneiss. 1 Gray, banded biotite-garnet gneiss. Thickness unknown. Some Grenville rocks which are more locally well developed are not included in the above list because their stratigraphic positions are wholly unknown. Among such rocks are the graphite schist, the white gneiss, and the sillimanite gneiss. The best extensive section within the quadrangle is shown by figure 1 which represents the succession of strata along a north- east-southwest line through the Grenville area between Oven moun- tain and Wevertown. The position of the section is indicated by the line EE on the geologic map. This is by no means a perfectly ‘continuous section, but the outcrops are numerous enough so that the condition of things shown in the figure can not be far wrong. A total of from 18,000 to 20,000 feet of Grenville strata appears to be shown in this section. The dip and strike of the strata are pretty constant the whole length of the section, and though the Oven mountain fault probably passes across the section it is not thought materially to affect the position and thickness of the strata. The hornblende gneiss toward the top of the section forms the prominent ridge which extends northward to the Hudson river. Figure 2 represents an east-west section across the valley one- third of a mile south of Daggett pond where there is an almost unbroken succession of nearly pure limestone whose total thick- ness is something like 3000 feet. On the west side, and dipping under the limestone, are some beds of hornblende-garnet gneiss. 16 NEW YORK STATE MUSEUM This bare appears to correspond with the lower part of the limestone mass in figure I. There is no positive proof that the quartizite shown in figure 3 is the same as that of the lower part of figure 1, but the two rock masses are of much the same character and both are of great thick- ness. This quartzite of figure 3, which represents a section across the valley between Chase and Bull Rock mountains, is nearly pure and shows a thickness of about 3000 feet with banded biotite-garnet gneiss dipping under it on the west side. Figure 4 is another fine section of the quartzite which also shows the underlying rock to be a banded biotite-garnet gneiss of unknown thickness. The limestone of the Valentine pond valley appears to dip south- ward under a thick belt of distinctly light and dark banded garnet gneisses, but just where these rocks belong in the columnar section can not be said. The quartzite in the area southwest of Thurman is often very tremolitic, which suggests that it does not belong with the other quartzités of the quadrangle. QUARTZ SYENITE As shown on the geologic map, the syenite covers about two- ninths of the area of the quadrangle and is distributed in very irregular shaped areas. Boundary lines between the syenite and granite can not be sharply drawn because of the gradation of the one rock into the other. Against the Grenville the boundary is generally not very sharp except where the Grenville has been faulted against the syenite. As regards granularity, structure and mineral composition the syenite is a very variable rock. The granularity ranges from fine to fairly coarse grain, with medium grain decidedly prevalent and with only rarely suggestions of a porphyritic texture. Evidence of crushing or granulation of the rock is common, especially in the cases of the more acid (granitic) syenites where the feldspars more than the other minerals are granulated. In structure the rock ranges from only faintly gneissoid to very clearly gneissoid, which is due to the arrangement of the dark colored minerals with axes parallel to the direction of foliation. All facies of the syenite are quartzose and the range in mineral composition is from pyroxene- quartz-syenite to granitic hornblende syenite as shown in table 1.’ 1J7n this and the succeeding tables only close approximation to the volu- metric proportions of minerals present is intended. . |e aro hal a A, ee fh ea es =a a < N a |e Ol-Lab Mrmr 25. |. 22.1. .°.- Bet 12 251214 } Said ey Cael ee Ol Seige | 15 | 25 | 15 14 | 18 I 10 | 1 {4 4 an ees nae Ol ) weet 25 125.1... . & 1/20 8 el ee + 1 | little Granitic hornblende syenite Ol ) | ek eae ee al Beemer rea ce (asst hf} 7 4 Ol 7 : ee jo Or ts. Se AEs Page AB a | 2 I ri Tae 3. | Ol | Ge ae | £0 | 35 2 ee Wa ho BAO Se Vale ys | 1 | 2 | little Ta pe el oe | Ol ) marmto | 5 + 65] 3 | 25 3 5 ah a Seip ee hs 4G eat ae The color of the fresh rock is the usual greenish gray of the Adirondack syenites, while the weathered surfaces are of yellowish brown to brown color. Because of vigorous glaciation even the weathered surfaces are hard, decomposed rock seldom being seen except in a few protected places on the south sides of mountains. Below this weathered surface it is usually not more than a few inches to the fresh greenish gray rock. That the syenite has been intruded into the Grenville is abund- antly proved by the many inclusions of all sorts of Grenville rocks, but most of these are too small to be represented on the geologic map. Some of the best examples of Grenville inclusions are ‘to be found in the mixed gneiss areas which will be described below. Pyroxene syenite. This syenite represents the most basic facies of the great syenite-granite intrusive mass. The generally faint development of gneissoid structure, low quartz and hornblende con- tents, and the presence of pyroxene are the chief differences be- tween this and the granitic hornblende syenite. The range in com- position is well brought out in table 1 which represents thin sections of carefully selected samples. The pyroxene is seen to be the most characteristic mineral of the rock. This pyroxene is of a beautiful green color, clearly monoclinic, 2nd shows good cleavages. is NEW YORK STATE MUSEUM Crystal outlines are sometimes distinct. Professor Kemp has noted a similar pyroxene in the syenite of the Elizabethtown-Port Henry quadrangles and he suggests the presence of the jadeite molecule ~ in its composition. Garnets seldom occur in this syenite. The most basic rock of all is shown by no. 1 of the table. This rock makes up the Bull Rock mountain mass. It is unusually high in plagioclase, pyroxene, and biotite and low in quartz, and is nearer the gabbro in appearance and composition than any other rock of the whole region. It is fine to medium grained and of rather a bluish gray than greenish gray color when fresh. Numbers 2 and 3 of the table are from the mountain 2 miles south-southeast of Riverside, and from along the road 1 mile west- southwest of Daggett pond respectively. In the field it is generally impossible to distinguish this pyroxene syenite from much of the granitic hornblende syenite and this, together with the fact that the two rocks grade perfectly into each other, renders separate map- ping practically impossible. The pyroxene syenite, however, is certainly less common than the hornblende syenite. Granitic hornblende syenite. The range in mineral composition of this rock is shown by the selected examples given in table 1. Microperthite and orthoclase are always present though in very variable amounts, while the quartz and hornblende contents are high and biotite is scarcely represented. In addition to the minerals shown in the table a few scattering garnets sometimes occur. No. 7, with its almost total lack of hornblende, is an unusual type. The gneissic structure is usually well developed though at times it becomes very faint. This granitic syenite on the one hand grades perfectly into the pyroxene syenite and on the other into the gran- ites below described. Arbitrarily, when the quartz content passes beyond 25 per cent, the rock is classed as granite and, as nearly as possible, the rocks have been separately mapped on this basis. The very common presence of biotite in the granite has also been a help in mapping. Numbers 4, 5, 6, and 7 are respectively from Potter mountain, 114 miles east of Pottersville, one-third of a mile north of the north end of Loon lake, and the summit of Little mountain. GRANITE As already stated, the granitic syenite passes through perfect gradations into the granite and these rocks are very clearly only different phases of the same great intrusive body. The rock is rather arbitrarily called granite when it contains more than 25 GEOLOGY OF THE NORTH CREEK QUADRANGLE 19 per cent of quartz. By becoming coarse-grained and porphyritic it also passes gradually into the granite porphyry. As in the case of the syenite, the contact against the Grenville is seldom sharp except along the lines of faulting. The area covered by the granite is almost the same as that of the syenite or about two-ninths of the quadrangle. | This rock, too, is decidedly variable as regards color, granu- larity, structure and mineral composition. The colors range through greenish gray, light gray, and pinkish to almost red. These color varieties are especially well shown in the vicinity of The Glen. Pinkish granites are the most abundant. The granularity of the rocks varies from fine to coarse grain, with a medium grain predominating. Coarse-grained types often show a tendency toward porphyritic texture and thus approach the granite porphyry. The granites are almost always highly granu- lated, especially the more gneissoid varieties in which the feldspars are most badly crushed. There is a wide range from poorly gneissoid rocks to those which are highly foliated and almost banded, the latter being particularly true of the commonly occur- ring pink granites. The range in mineral composition is well illustrated by the se- lected examples given in table 2. As compared with the granitic syenite, the chief differences are the high quartz content, the com: mon occurrence of microcline, the generally lower content of horn- blende, and the almost constant presence of biotite. TABLE 2 Granite g | | = o 3 C7) 2 oo | v a 3 & & | & 2 a ToS 3) S “A ra) 77 @ Px: Sis) es | ies Po a eg a a bp Q 9 t se as Ss 3 3 oe {x a= e a a he el a a ee A, (oS a = eS a) a N = < GE Tare ee ae a a | erat}: 22} 22 Pema baOnh 2a Lace awe: little ee Ol | 7135 | 7 | 30°)/%8 eee et Te Ra dene ee! 07 | SY Peseta et | a eyia 7 Vda ae ears Reon | little BS ey ) Ol-And ) | ) | ) 4{|53|10/ 45} 4 $.+30°) 5 | 2 i | ee Ol-And | Wy 6432 4) 40d, 10 35 | 7 Me Sy eee 4 | 1 | little Ol | : 6| 31 | 10| 18 | 14 10 | 35 6| 2 a a 1 | ye ) 20 NEW YORK STATE MUSEUM Number I is a fine example of a transition rock from a granitic syenite to granite as seen along the river in big ledges one-half of a mile south of The Glen. The color of the rock is pinkish gray. Especially noteworthy are the comparatively low quartz and ep hornblende contents, and the absence of microcline. Number 3 is typical looking pink, biotite granite from the ere ridge just west of Crane mountain. Number 6 is a very quartzose, hornblende, biotite, pink granite with considerable microcline as seen in excellent outcrops along the road 1% miles south of Riverside. Only a few of the observed masses of Grenville or mixed gneisses which occur within the granite are large enough to be shown on the geologic map. Small inclusions or stringers, sometimes sharply — outlined and sometimes seeming to grade into the granite, are very numerous. Only a few examples will be cited. Thus, a large, homogeneous mass of very typical granite, one-quarter of a mile — above the mouth of Glen brook, contains a number of clear-cut — Grenville hornblende gneiss inclusions. These inclusions are mostly long (10 to 20 feet), narrow stringers which are drawn © out parallel to the foliation of the granite. Similar inclusions are common I mile south of The Glen along the east bank of the river, and in the Mill mountain mass. On the west bank of the Hudson river and just opposite the Ferry (east of Heath mountain) a ad ledge of coarse-grained hornblende granite contains ten or fifteen fine examples of small (none over 3 feet long) very angular in- 7 clusions of Grenville hornblende gneiss. Features of special interest in connection with the granites are the frequent and comparatively sudden transitions from the gray to pink varieties, and from the more syenitic or basic facies to the more truly granitic facies. The effect is to give wide bands or — layers of varying color and composition and yet all clearly belong- — ing to the same rock mass because of the true gradation of one layer or band into another. Among many places where such phenomena have been observed are in the vicinity of The Glen, | and along the road one-half of a mile north of the north end of — Loon lake. The writer has already described similar occurrences © in the region of the Port Leyden quadrangle.1 Professor Kemp, in the bulletin on the Elizabethtown-Port Henry region, has re- cently described and suggested an explanation for similar but even more extreme phenomena as follows: “The most acidic variety will quite sharply replace it [the syenite]; and in the same way a LN. Y: State Mus, Butlers: ip. 06-17; GEOLOGY OF THE NORTH CREEK QUADRANGLE ZI very basic variety may come in and constitute the section for 50 or 100 feet or more. Yet, while the transition is sharp, there is no evidence of separate intrusive masses nor is one justified in inferring more than a differentiation of an eruptive mass into layers or portions of contrasted composition. .,. . That this differentiation takes place in magmas is one of the growing con- victions of students of igneous rocks.”! Now, so far as the writer's observations in the North Creek region are concerned, they fully accord with Professor Kemp’s interpretation of this puzzling phenomenon. Of course, the rocks have been severely compressed and possibly folded and the banded effect may thus have been ac- centuated, but nevertheless there appears to be no getting away from the apparent fact-of some sort of differentiation of the granitic magma into layers of varying composition. GRANITE PORPHYRY This rock represents another phase of the great syenite-granite intrusive mass and always shows a perfect gradation into either the granite or syenite, so that sharp lines of separation between these rock types can not be drawn. On the accompanying geologic map this rock is seen to be rather widely distributed in small to large irregular shaped areas making up altogether perhaps a little less than one-ninth of the area of the quadrangle. A very similar rock. occurring in the vicinity of Northville has recently been de- scribed by the writer? and that description applies almost perfectly to the North Creek granite porphyry. Exactly the same evidences which were presented to prove that the Northville granite porphyry is really only a facies or differentiation product of the great syenite magma, may also be applied to this granite porphyry. Still more recently. such rock has been found by the writer in the northern portion of the Lake Pleasant quadrangle. Thus it is quite certain that granite porphyry is a rather widespread rock in the southeast- ern Adirondacks. The typical rock is gray to pinkish gray, thoroughly gneissoid, end with beautifully developed porphyritic texture. The pheno- crysts of feldspar are usually from one-half to one inch long and more or less flattened parallel to the foliation. Carlsbad twins are often easily recognizable. Feldspar, quartz, and biotite or horn- blende are always plainly visible to the naked eye. Often large IN. Y. State Mus. Bul. 138, p. 48 and 128. 2N. Y. State Mus. Bul. 153, p. 17-20. bay j 22 NEW YORK STATE MUSEUM quartz crystals are also decidedly flattened parallel to the folia-— tion. The phenocrysts are embedded in a fine to medium-grained matrix of feldspar, quartz, and biotite or hornblende. The rock : nearly always shows the effects of dynamic metamorphism, the — more or less crushed and granulated feldspars generally being ~ clearly visible to the naked eye. The degree of foliation often varies considerably from place to place, and the porphyritic tex- ture, especially along the borders, becomes notably less prominent. The general range in mineral composition is shown by the examples given in table 3. TABLE 3 Granite porphyry a o as; o Br ei/ 2] 3 E 8 . a — = oO — She ial tench ule 8 $1) ae ae ae fe aa 2 2 3 ie) eo ha so H Ss ae | fo) 3S ae) rs] ree ee ere a Ei $6 18 8 ele 8 5 | Se) ee A, Oo Ra ea S < o Ol-Aad ; eee wali cae I | 44 4 4 2 z ate | Ol-And 1 ib; & ; Po) 20.) Ona LO. 2s 5 | 30 | Io I ra = Z & a Bel TR eOal BO Me pbs oe eas 204° 8 i fam ees = = z ce Ol-And ay Oe 8.135 8 7b BO ue I + 4 he Number I is a very typical looking granite porphyry from the _ quarry at Horicon., This is Hie rock which Professor Kemp de- — scribed as the “ Horicon gneiss’ some years ago.! Number 2 is from Kelm mountain; no. 3 from one mile south of Kelm mountain; and no. 4 from the south base of Prospect mountain. ;’ A good example of a rather coarse, somewhat porphyeias inl granite which might almost pass for a granite porphyry occurs in the quarry along the,road 2 miles northeast of Pottersville. , It so happened that no Grenville masses within the granite por- ie phyry were of sufficient size to be indicated on the geologic map. but in the field one may see a good many small patches or streaks of Grenville gneiss sometimes as clear-cut inclusions and at other — times seemingly more or less fused into the granite, thus giving — ‘5 a very locally a sort of mixed gneiss effect. el 1 77th Aaa Rep’t N. Y. State Geol. 1897, p. 510, 541. GEOLOGY OF THE NORTH CREEK QUADRANGLE 23 MIXED GNEISSES In the areas mapped as mixed gneisses, the rocks are more or less intimate associations of the various Grenville, syenite, gran- ite, and granite porphyry gneisses. They are really areas of Gren- ville which have been all cut to pieces, and in some cases appar- ently partially fused, by the great igneous intrusives. In some areas true Grenville rocks predominate; in others true igneous rocks pre- vail; while in still others the most common rock appears to be of intermediate character due to an actual melting and incorporation of Grenville sediments by the molten intrusions. Except along fault lines, these mixed rocks everywhere grade into either true Gren- ville or syenite or granite and the drawing of boundary lines is largely a matter of personal judgment. Any attempt to separate the various members of these mixed gneiss areas would be un- satisfactory because of the general insufficiency of outcrops and the small scale of the map. There are many places within the quadrangle where, as a result of more or less perfect assimilation, rocks of intermediate com- position occur on both small and large scales. One and one-third miles northeast of Kelm mountain and near the map edge there are fine illustrations of dark Grenville garnet gneiss inclusions in the granite porphyry, the inclusions usually grading perfectly through zones of a few feet into the granite. The intermediate rock is coarse-grained, very garnetiferous, and not so porphyritic as the true granite porphyry. Similar cases of local assimilation by granite porphyry, granite and syenite have been observed at other places within the quadrangle. On a large scale, perhaps the best examples of rocks of inter- ‘mediate character make up most of the mixed gneiss area just east of Chestertown. Thus the whole top of Prospect mountain consists of gray, fine-grained, very massive rock which has the composition of a biotite granite. This rock is quite homogeneous except for occasional patches or stringers of gray Grenville gneisses which are fused into the mass. Passing southward and southwest- ward down the mountain side, this rock grades perfectly into a medium-grained, gray, biotite granite which contains very few Grenville inclusions, and this rock, in turn, grades perfectly into the typical biotite granite porphyry at the base of the mountain. Passing westward down the mountain side, however, the fine- grained granitic rock at the top gradually becomes coarser grained and contains more numerous and more clearly defined inclusions 24 NEW YORK STATE MUSEUM of Grenville gneisses, with these rocks, in turn, grading into pure sa Grenville on the other so that there appears to be no escape from _ the idea that these gray, granitic rocks were formed by actual fusion and incorporation of more or less of the Grenville into the is granite porphyry magma. The presence of the inclusions does not necessarily oppose this view because they may well enough simply represent fragments of Grenville which were caught in the granite — magma just before consolidation or when the temperature was not high enough actually to melt the fragments. Gray granitic rocks ~ of apparently the same origin are common throughout this mixed ~ gneiss area. Another interesting mixed gneiss area is the one just north of the village of Horicon. In the vicinity of the quarry, at the base i of the mountain, the rock is very typical granite porphyry which contains a few long, narrow, sharply defined, Grenville gneiss in-_ clusions. Going up the mountain side from the quarry, the granite porphyry, which at times (in patches or wide bands) appears typi- 4 cal, is intimately associated with Grenville. This Grenville occurs: : as large and small inclusions, often sharply defined and nearly al- ways drawn out parallel to the foliation. The included rocks are ~ chiefly banded biotitic, hornblendic, and quartzitic gneisses often ~ in bands from 20 to 30 feet wide. Toward the top of the moun-— tain the rock is mostly like the gray granitic rock already de- scribed as occurring at the top of Prospect mountain, and the ! inclusions are fewer and not so sharply defined. Here again this — granitic gneiss appears to be an assimilation product, while farther down the mountain side the temperature seems not to have been high enough to cause any considerable melting or assimilation of the included gneisses. 4 In the large, mixed gneiss area south of Henderson mountalll there are many fine illustrations of very intimately associated Gren- ~ ville and gray granitic rocks, the Grenville often having been more or less melted into the granites. The granites predominate and some of them at least are thought to be assimilation products. Such phenomena are well exhibited from Igerna southwestward to” the river. | In the mixed gneiss area which borders the Chase-Kelm moun- tain granite porphyry mass on the west, the prevailing rock is a 4 i oe “iam seal ws W. J. Miller, photo View showing contact between Grenville limestone and granitic syenite as seen from across the Hudson river one-fourth of a mile north of the ferry (southwest of Moon mountain). The smooth ledge at the river’s edge on the left and another toward the upper right hand corner are parts of a single mass of syenite mostly concealed by the trees. The other rock is Grenville limestone (white) with numerous closely involved streaks and bands of hornblende (dark) gneiss. The sharp contact between the syenite and Grenville is not well brought out in the picture. GEOLOGY OF THE NORTH CREEK QUADRANGLE 25 gray, medium-grained, biotitic, granitic gneiss which is intimately associated with some Grenville gneiss. Here again it is quite cer- tain that the granitic gneiss forms a border zone between the gran- ite porphyry and the Grenville, where the former has more or less assimilated some of the latter. Along the southeastern base of Moon mountain there are excel- lent exposures of Grenville much cut up by, and often fused into, syenite. The mixed gneiss area at the southwestern corner of the map affords many fine examples of syenite or granite and Grenville closely involved and fused together. There are also many well- defined inclusions or stringers of Grenville scattered through the igenous rock. These phenomena are especially well shown on Wolf Pond mountain. The mixed gneiss area which surrounds Heath mountain con- sists very largely of Grenville gneisses and limestones through which numerous small masses of syenite or granite have been in- truded. The most interesting exposures occur along the river for nearly a mile northward from the Ferry. About 1 mile north of the Ferry and on the east side of the river, are great ledges of Grenville limestone and-hornblende gneiss, these rocks being badly contorted and broken and containing some patches of good syenite, 10 to 30 feet across, and completely surrounded by either hornblende gneiss or marble. At the same locality a large mass of syenite overlies crystalline limestone and shows the actual sharp contact for fully 100 feet, there being no particular contact phenomena (see plate 3). About one-half of a mile north of the Ferry, and along the road, there are several very interesting inclusions of Grenville limestone in the syenite. Two of these inclusions (one being 3 or 4 feet across and the other 20 feet long and 2 to 4 feet wide) are com- pletely surrounded by, and in very sharp contact with, the syenite. The limestone. is coarse, crystalline, calcitic, and contains graphite. At the contacts small green pyroxene crystals are often common. The small area near Daggett pond is of interest because the Grenville is there interbanded with granitic syenite, the bands of each rock often being 20 to 40 feet wide and the contacts pretty sharp. One Grenville band is a garnet, pyroxene gneiss, while others are biotite or hornblende gneisses. The area of mixed gneisses lying to the east of Stockton and Gage mountains shows numerous exposures of closely associated 26 NEW YORK STATE MUSEUM syenite or granite and Grenville gneisses in about equal amounts. There are few suggestions of assimilation, the igneous and sedimen- tary rocks generally retaining their characteristic features. The other mixed gneiss areas require no special mention. THE GABBRO AND ITS DERIVATIVES Because of the large number of exposures, mode of occurrence, excellent outcrops, frequent contacts against the country rocks, and the remarkable variations in composition and appearance the gabbros are of unusual interest and will be described in considerable detail. Mode of occurrence The gabbro and its derivatives nearly always occur in the form of small stocks or bosses rather than as true dikes, their length ranging from 30 to 4o feet to about a mile, and with widths up to three-fourths of a mile. Sixty-one separate gabbro bodies were found and are shown on the geologic map. In spite of the detailed field work a few others have prebably escaped the writer’s notice. The ground.plan, as represented on the geologic map, is almost — invariably elliptical, though sometimes approaching the circular. When the contact with the country rock is carefully traced out it is commonly found to be sharp and shows smooth or flowing out- lines against the country rock. In only two or three cases do the gabbro masses approach the true dikelike form, and in each of these cases fine-grained tongues were found to extend into the surround- ing rock. One stock, one and one-third miles southeast of Chester- town, shows several such tongues, one of them (1 to 6 inches wide) clearly cutting the granite porphyry for 30 feet. Other and smaller gabbro dikes at the summit of Hackensack mountain, and 1 mile south of South Horicon show a number of such fine-grained tongues. At one place in the dike or boss which crosses the road 1% miles © a little west of south of South Horicon, fairly coarse-grained gabbro is in sharp contact (for 6 or 8 feet) with fine-grained gabbro, the latter becoming coarser grained again away from the contact. This suggests a second intrusion of the gabbro after the first but after the first had cooled. | It is a striking fact that in spite of many. excellent contacts which were observed, such dikelike tongues are so rare. As Harker says’: “Although most of the bodies of granite and other plutonic rocks 1 Natural History of Igneous Rocks, 1909. p 86. GEOLOGY OF THE NORTH CREEK QUADRANGLE 27 which have been loosely described as bosses, and so rendered in ideal sections, are doubtless of laccolitic or other stratiform shape; some, not of the largest dimensions, appear to have a pluglike form, with more or less vertical boundaries.’’ The small stocks or bosses of the North Creek region are certainly of this pluglike or pipelike form as shown by the very character of their eroded cross-sections and also by the vertical contacts with the country rock. Among the many fine contacts. which came under the writer’s observation, not a single exception to the rule of vertical or practically vertical con- tacts was noted. In most cases the long axes of the stocks lie parallel to the folia- tion of the inclosing rock, though there are some notable exceptions. It would therefore seem that the molten intrusives generally followed the lines of least resistance but, even in these cases, the broad ends of the stocks cut sharply across the foliation bands, sometimes for a distance of several hundred yards. Such a phenomenon is well! exhibited at the south end of the large stock just south of Mountain Spring lake where a big quarry has been opened up along the contact. The gabbro stocks are not at all uniformly distributed over the area of the quadrangle, the largest number being confined to a nearly north-south belt with a width of from 3 to 5 miles and extending through the middle of the quadrangle. This belt roughly corre- sponds to the general strike of the foliation. A secondary belt, about 1 mile wide and 5 miles long near the middle eastern bound- ary of the sheet, contains a dozen small stocks. With a single small exception the whole western side of the quadrangle is devoid of gabbro masses. In the northeastern portion a few stocks occur, but they may really belong to some other belt not yet mapped. Thus we see that the gabbro intrusions were limited to rather well-defined areas or belts. Among these gabbro stocks four types of occurrence are especially noteworthy as follows: (1) The normal, dark, basic gabbro with diabasic texture and usually homogeneous throughout; (2) gabbro chiefly of the normal type but with irregular patches or masses of lighter colored rocks of syenitic or dioritic make-up, these patches blending with the normal gabbro; (3) the whole stock made up of lighter colored, more acidic rock; and (4) any one of the above types with blocks or inclusions of the country rock. These four types are all primary variations. Examples of the last three types will be given later. 28 | NEW YORK STATE MUSEUM Megascopic features The gabbro and its derivatives present a truly remarkable number ~ of facies or varieties clearly visible to the naked eye. The coarse- § ness of grain varies from the merest fraction of a millimeter to fully an inch (for example, the stock on the south side of Loon lake). The fine-grained portions are confined to the borders of the stocks or the few branching tongues and were caused by the more rapid chilling of the rock in those positions. Even the finest grained rocks, however, are holocrystalline. As a rule the coarseness of grain in- creases toward the interior of the masses, though often medium to ~ coarse grained rocks extend to the very contact. The typical or prevailing gabbro shows a medium grain; that is, the grains are from I to 5 millimeters across. The texture varies from coarse to medium to. fine-grained gran- itoid, to medium to coarse-grained diabasic (ophitic). The gabbro from the stock on the south side of Loon lake is an excellent example of diabase texture in which the feldspar laths attain a length of an inch or more. The typical gabbro always exhibits the diabasic texture. In color, the gabbro and its derivatives range from nearly black — through dark to light gray, the darker varieties often showing a ~ slight reddish tinge due to the presence of garnets. The gray rocks all belong to the more acidic (dioritic and syenitic) facies described — below. In one case a greenish gray color was noted. The very dark ~ color of the typical gabbro is due to the fact that the ‘eka are so charged with tiny black inclusions. In the typical gabbros the minerals commonly recognizable with the naked eye or hand lens are plagioclase, pyroxene, hornblende, garnet, biotite, and ilmenite, while in addition to these orthoclase and quartz may often be seen in the more acidic phases. Except for the rather common presence of highly gneissoid to even schistose amphibolite borders, the stocks of typical gabbro are practically devoid of gneissoid structure. Some of the lighter colored, more acidic phases, howe yes: show fairly well-developed foliation. It is important to note that many of the above described varia- tions may be found within a single stock as, for example, south of Mountain Spring lake. The following statements from Smyth's description of a similar western Adirondack gabbro! fittingly apply here: ‘“‘ These [primary] changes in character take place very sud- denly, and the different phases are most irregularly distributed, — Nene, ae: Sci, April 806; pi 273278 : * ma _ _ is W. J. Miller, photo A typical exposure of gabbro as seen three-fourths of a mile south-south- west of Loon Lake mountain. Note the very irregularly jointed character of the rock and the whitish mass of pegmatite cutting the gabbro in the lower left-hand corner. GEOLOGY OF THE NORTH CREEK QUADRANGLE 29 seeming to conform to no law. . . . These primary variations in the rock suffice to give considerable diversity to different portions within a limited area, but this diversity is greatly intensified by cer- tain secondary modifications of structure and composition. As a result of the combined effect of primary and secondary variations, it would be easy to collect, within an area of a few square rods, a half dozen or more specimens whose appearance even in thin section would scarcely suggest that they had any connection with one an- other.” Cushing says! of the Adirondack gabbros in general that they show much variation, both primary and secondary, from place to place. Both of these investigators proceed to discuss the sec- ondary variations and their causes but, so far as the writer is aware, little or no attention has been given to the causes of the primary variations which will be considered below. Microscopic features Mineralogical composition. The following table will serve to show the great range in mineralogical composition of the gabbro and its derivatives. The figures refer to percentages by volume and are meant to be close approximations only. TABLE 4 Mineralogical composition of the gabbro and its derivatives — o o| ¢ o o 56134 3 z a o yA iets) i) =| 2 So = o » N v co) 2 el ie ae) pee: le oa Ga meee? e-em t ha = W = = = 3/5 bo a} Ol Sl) a] & ‘eects |e a | 2 3) ae i 3 = |] & of} & | a{-s E OE oo Bae 3 5 = > a a = na|O AY Sip baccarat) hs * Eal IN [eres ee QIN N < eo) e I] 45 Lab. 50 [i hee) ae Ben Via 9 CT ash i eel Re Roehl Ge Pe pee bin AoE ae 2} 6 Lab. 50 Si 27 7 I} little| 8 LL eam DG be gros OE Side on) | aa 3) 214.5} Ol-Lab. 38] 27|12.5] 3 2.5 Via lowes eS ee ed Pees MPP D UCN es tele occa | Pee 10 | a ce little little Kan edt oes! Ol-Lab;. 57) Ts)... . are well known in many. basic rocks, are exhibited in a truly re- fe W. J. Miller, photo Photomicrographs of thin sections of gabbro from the stock on the south side of Loon lake. Each magnified 15 diameters. In the upper figure the large central mineral is olivine completely sur- rounded by successive rims of hypersthene, biotite (narrow and dark), and garnet. Surrounding all are broad laths of labradorite. In the lower figure the large, black, central mineral is ilmenite, followed by successive rims of biotite, hornblende, garnet and biotite. The second and third — biotite and hornblende — rims are not separable in the photo- graph. Surrounding all are labradorite crystals. W. J. Miller, photo Upper figure. Photomicrograph of thin section of gabbro from the top of Hackensack mountain. Magnified 15 diameters. The central mineral, with good cleavages nearly at right angles, is diallage which is almost completely surrounded by a zone of hornblende (darker colored). As seen under the microscope the rim is very clearly defined. The light gray minerals are basic plagioclase. The diabasic texture of the rock is well shown. Lower figure. Photomicrograph of a thin section of diabase from the dike one and one-half miles southeast of Johnsburg. Magnified 15 diameters. The long, slender prisms with transverse cracks are augite; the smaller, more numerous, prisms arranged in more or less sheaf like bundles are basic plagioclase; the black areas are glassy groundmass; and the four small, white rounded areas represent quartz, probably of secondary origin. GEOLOGY OF THE NORTH CREEK QUADRANGLE ae markable manner in the North Creek region gabbros. In the ex- amples most often described the core is olivine, but in the gabbros here considered the writer has observed cores of olivine, hypers- thene, ilmenite, augite, and diallage with from one to five distinct, successive rims surrounding the cores. Professor Kemp has de- scribed! and figured a number of interesting examples of reaction rims observed in certain gabbros of the eastern Adirondacks. The following nine types of reaction rims comprise most of those noted by the writer in the North Creek gabbros: 1 Ilmenite surrounded by hornblende. 2 Diallage surrounded by hornblende. 3 Augite surrounded by hornblende. 4 Hypersthene surrounded by garnet. 5 Hypersthene surrounded by successive zones of biotite and hornblende. | 6 Olivine with successive zones of hypersthene, hornblende, and garnet. | 7 Olivine with successive zones of hypersthene, biotite, and garnet. 8 Hypersthene with successive zones of biotite, feldspar, and garnet. ; 9g Ilmenite with successive zones of biotite, hornblende, garnet, and biotite. In nearly all cases the material immediately inclosing the rims is feldspar which, in a sense, adds another zone to each of the above. No. 6 is like one of those described by Kemp. No. 9 is a remark- able example and, because of its additional outer rim of biotite, is even more interesting than a case described by Lacroix.2 Some of the others may be new examples. The material of each rim appears to be highly granulated or at least made up of numerous small grains. It seems certain that where hypersthene envelops olivine, the former has secondarily developed from the latter. The olivine cores are of very irregular shapes and in all sizes. Where hypersthene forms the core it is probable that all the original olivine has been altered to hypersthene. The common occurrence of hornblende rims around pyroxene strongly suggests the derivation of the former from the latter. Garnet is almost invariably in contact with feldspar which suggests the partial formation, at least, of the garnet from the feldspar. we Geol. Soc. Amer. Bul., 1894, 5 :218-21. 2 Bul. Soc. Min. Fr., 1889, 12 :232. 32 NEW YORK STATE MUSEUM Chemical composition, norm, and mode "7 Excellent exposures of what is regarded as very typical gabbro_ occur in the railroad cut 114 miles south of The Glen. This rock has been analyzed for the writer by Prof. E. W. Moma + TABLE 5 Chemical composition and norm a o i, Ss a oo 1a jo a, ‘ te H » a me) ‘i ‘ & s |8\2/\2) 2612) eae me | eam SIO) ae AGAIN ie iF a ee el RE vee 168).02.0) aes 69) +4 «i 1G Fae te TA.17|"..1399|.- 12. .fe. 1...) 12) 43h Bas eee oa io eh ee 2509 SetOL Alan ie dnteuae 13\, 3. eeee eee ‘ CO) fae ee Ge 12) ele) g2Ole ol ee Bibs usr \mas Beemer ties = MgO 4.94 rsa] 38-1) 2c lala 10 Se0 Be "§ CAO) une O65). 2.172) “dl 20lk. Soke eam eee ee O8ieras i res 3 NaaQ-. co23 BOTA SOON ai clictaa: TA Scale AZ). 3)... scien 7) ica Ae [ean PLR 0 22 eheeee eM Un al Bree T2!. be) oe lee ae z ERO. hs copt PR Mae oe falas eal es Meee 4 HBO ne. SEIS ios sly Ao Gallare — nes Bie cate .24 ae HOD ss £508 BLOB: K.0!+Na,0! 62 5.3 _ a ; 1B) ne C7. 53 Bem 45.03 Rage. . aaa >= 3, Campton ‘ Hyper..... 8.02 CaO! 84. 3° Sie . : i} Oliv SU 2 K.O! : HO +ZrO2. 32 } Subrang, — C2 en Camptonos : Na;O! © 550, ae 5, GEOLOGY OF THE NORTH CREEK QUADRANGLE 33 TABLE 6 Mode of gabbro | / | Ressired | Rel. vols. S. G. esa Aaa higher eg Plapiocilase......... 2 805 38.09 2.66 7 461 22.72 Orifeeiase......... 335 4.55 2.56 858 | a577 Hornblende........ I 990 27.02 3% 20 6 368 | 27292 Hypersthene........ 932 12.65 3.50 3 262 | 14.30 a 505 6.86 3.20 I 616 | 7.09 er 22 3.08 3.30 749 | 3.29 Se 265 3.59 3:70 980 | 4.30 SS 184 2.50 Seay Q5I | 4.47 2 95 1.29 5.00 475 | 2.08 PR se 26 oak 3.20 83 | 36 | 7 364 LOTR! Fe aid (Me mee ate | 22 803 | 100.00 Under the old qualitative system the rock is a hornblende norite, while according to the quantitative system it is a hornblende-camp- tonose. In thin-section the plagioclase is seen to range from oligo- clase to labradorite, and the analysis and mode show that the average composition is that of a basic andesine. The high TiO, of the an- alysis shows either ilmenite or very titaniferous magnetite, the ilmenite being far more probable because of the difficulty of other- wise accounting for such a low content of Fe,O,. 34 NEW YORK STATE MUSEUM TABLE 7 Adirondack gabbro analyses compared I 2 3 4 5 6 7 SOE. os. Sih eee 46.40 | 47.88 | 47.42 | 47.16 | 46.74 | 44.07 |) ae ls Os .o°5 Tekno eters 14.17\|. 18.90 | 17.34 | 14.45 | 16.623 | 15740 12.46 Beis. 2c eee 2303 L.390)) 4-01 168 2 ee, 2.29 4.63 Be)... «0 sae 13.12 | 10.45 |\10.22 | 13.81.) 10°60 7ang ae 12.99 MigQ' =. Ce Neceeoteaanie 4.94.45 °7.10 | 5:21 5.24 | 6198 ees 5.34 CaO, ;, 2 .ok eee 9.65.1; 8.367). 8.00 |) 8,12 8.66 | 7.50 10.20 NazOn. 2a eee BT 2 75a. 3. Ao\,| 200 3.81 3 702 2.47 IOS, Seer 1,k2 81 1.89 1.20 .86 .56 95 sO ke ae es 27 61 T<13 .60 .85 .75 60 COb opt + Rea ike cele nen aN eae 35 O71 vie 37 TOROS Sik nen eee ees anos 1.20 3.60 2:27 2.54 1.18 5.26 EO esi ee ines Mee 80 20 .06 .57 33 14 28 PR es eer ee 14 HOTOW GS Seep Be a II 06 26 V4 G0) @) Ra son ye ura fe tae 44 .16 06 24 26 22 17 NOC at yatrea cE io er eis (O72 He Gane 02 03 o2 | aia EAC recy etn oe meet tala pata. mete Uy So cot OMG he | gil: Race Bilee RS cl Gite ates etn rr 02 rao Ue Ae hs atone STEEN oe oth tetee 21. |.....2 | Uo Ursin csi baw tate hae Of | cece fo eee dy aie ts Sc QO we Peco ie a sce ke is irs | howe nea O4 | oe.) |). s 2a SOT aR Cee eee TO fw. f0. Qe aeee Poa ec |) 2 ge iO ane Wen met SEI ae eer O5 [ow 2e bee) Pk i rrr 99.77 |100.02 |100.01 | 99.98 | 99.77 | 99.72 | 100.75 1 One and one-quarter miles south of The Glen, Warren County. E. W. — Morley, analyst. Described by W. J. Miller. t 2 Split Rock Mine, Westport, Essex county. W. F. Hillebrand, analyst. — Described by J. F. Kemp. 3 Dike near Nicholville, St Lawrence county. E. W. Mom: analyst. y Described by H. P. Cushing. 4 Woolen Mill, one mile west of Elizabethtown, Essex county. W. F. Hillebrand, analyst. Described by J. F. Kemp. 5 Two miles south of Elizabethtown, Essex county. W. F. Hillebrand, analyst. Described by J. F. Kemp. 6 Same SePOsune as no. 5. W. F. Hillebrand, analyst. Described by J. F. Kemp. 7 Lincoln Pond, Essex county. George Steiger, analyst. Described by J. F. Kemp. o These analyses show the Adirondack gabbros to be very similar in composition, the only notable variations being in the contents of — Al,O,, MgO, and TiO,. The North Creek sheet gabbro (no. 1) agrees most closely with no. 4. Cause of the primary variations In attempting to account for the primary variations of these gabbros, the writer believes there is strong evidence favoring the application, to a greater or lesser extent, of Daly’s magmatic stoping GEOLOGY OF THE NORTH CREEK QUADRANGLE 35 and assimilation hypothesis to the solution of the problem. For full discussions of this hypothesis the reader is referred to Daly’s original papers.’ Some of the more fundamental principles are as follows: Batholithic (or stock) magmas have reached their present positions chiefly by the successive engulfment of blocks of country rock (xenoliths) stoped or broken out of the roof and walls of the magma chamber; the xenoliths become immersed and dissolved in the depths of the original magma with the formation of a second- ary magma; when the magma becomes very viscous (due to cool- ing) the xenoliths neither sink nor become dissolved. Only a summary of the application of these principles to the North Creek gabbros will here be given, the writer having more fully discussed this matter in a recent paper.? We have shown that the gabbro stocks are of the pluglike or pipe- like form with practically vertical boundaries. Such igneous masses were not intruded by simply displacing or pushing aside the country rock, but rather there was a process of replacement. Thus the mode of occurrence of these stocks furnishes strong evidence in favor of magmatic stoping as an important factor in the intrusion. The very presence of the inclusions as xenoliths proves that the process of stoping or rifting off blocks from the chamber vault actually did take place to some extent at least, and this when the magma had cooled to a highly viscous condition and hence had com- paratively little power to stope and too low a temperature to assimi- late the blocks. Thus the occurrence of such xenoliths is quite in harmony with Daly’s hypothesis. The writer believes that the more acidic patches or masses (al- ready described) within the gabbro stocks are evidence of chemical change within the intrusive magma due to solution or partial solu- tion and diffusion of blocks of country rock. In such cases the magma was just hot enough to melt or partially melt and only par- tially diffuse the blocks of country rock. Five or six of the stocks are composed wholly of rocks more acidic than the typical gabbro. In the earlier stage of very active intru- sion the invading magma was more thoroughly molten and as the blocks of country rock were stoped off they sank in the magma and became thoroughly dissolved and diffused. Since the country rock was nearly always syenite, granite, or gneiss the magma became more and more acidic. 1 Amer. Jour. Sci. 1903, 15 :260-08; Amer. Jour. Sci. 1903, 16:107-26; Amer. Jour. Sci. 1908, 26:17-50. “Jour. of Geol. 1913, 21 :160-80. 2 36 NEW YORK STATE MUSEUM Contact phenomena A very interesting case of contact metamorphism produced by the action of the gabbro on granite may be seen at the southern’ end of the large stock just south of Mountain Spring lake. In a recently opened stone quarry, and about 75 feet higher than the road © on its east side, the rocks are laid bare in such a manner that an excellent opportunity is afforded for the study of the contact zones. © The following nine zones, passing from the typical gabbro to the typical granite (country rock), have been studied in detail in the © field and by means of thin sections and hand specimens. Zone 1 Typical gabbro well within the gabbro stock. Nearly blacks medium grained, and with diabasic texture. (Gradation © from I to 2) Zone 2 Syenitic phase of gabbro stock and within a few feet of the granite. Dark gray, medium grained, and with granitoid ii texture. (Gradation from 2 to 3) Zone 3 One to three feet wide. Biotite-schist, border phase of the | | gabbro stock. Secondary origin. (Sharp contact betwees ni 3 and 4, gabbro and granite) 7 Zone 4 Four inches wide. Hornblendite phase of the country rock Nearly black, medium grained, banded parallel to gabbral O- granite contact. (Fairly sharp contact between 4 and 5) | Zone 5 Six inches wide. Monzonitic phase of the country rock. Yellowish gray, medium to coarse grained, and banded parallel to the main contact. (Not very sharp contact between 5 and 6) | , : Zone 6 Fifteen to eighteen inches wide. Chiefly hornblendite phase of the country rock but with numerous very narrow streaks of no. 5. Nearly black, medium grained, and banded parallel to the main contact. (Sharp contact be- tween 6 and 7) 3 Zone 7 Three and one-third feet wide. Monzonitic phase of the country rock like no. 5. Yellowish gray, fairly coar: grained, and banded parallel to the main contact. (. Not very sharp contact between 7 and 8) q Zone 8 Seven feet wide. Monzonitic phase of the country rock Light gray, fairly coarse grained, and not banded. (Gra- dation from 8 to 9) : | ' Zone g Typical (country rock) granite. Pink, medium grained, and very gneissoid but with gneissic barids striking at almost right angles to the main contact. Plate 7 W. J. Miller, photo Photograph of a hand specimen showing the contact between diabase and Grenville limestone from the Asbestos mine three-fourths of a mile southeast of Thurman village. Nearly natural size. The zones numbered on the left side correspond to those described on page 43. Zone 4 is scarcely brought out in the picture and zone 3 is best shown on the right side. GEOLOGY OF THE NORTH CREEK QUADRANGLE a7 TABLE 8 Mineralogical composition of each contact -zone = | i | 2 | | | us) Oo 3 o Payee mee Nhe iti = 1 x) © + mie | =| = | Beam} ee) a | 2] oe | os & | o | Ob-lab | | | I <6 es! 45 tA | ZO 6 2s aaa a UI ea a I 2 | Ol-lab | | | SS eae eee | "1102s Mere) 8 le eg Seeeaey Pr 8 BoP MELE Loo a x4 | dtttles)). 5 3 | Biotite-schist with some feldspar | | | 4 | Like No. 6 | | | | | / . Ol-and | / | ha oe oe eae rs ee) Wentte- 4 Ettle: | os... ) Ol-and | | > a Ge ee tae ON = 3 | little 7 | Like No. 5 / | Ol-and ) ) 8 | 33 Be Me eh htc tall 2 = + | little | ) Ol-and | | 5} 40/|151 4 5 Ola ve sae Oren | Peake 3 . | A noteworthy feature is the fact that the strike of the foliation of the very gneissoid country rock is nearly at right angles to the gabbro-granite contact, while the clearly defined contact zones are parallel to the contact. Other features of special interest are the syenitic border (except for the secondary biotite-schist) of the gabbro near the contact, and the almost complete absence of quartz from the granite within a dozen feet of the main contact. Thus the country rock (granite) is distinctly more basic near the contact, while the gabbro is dis- tinctly more acidic near the contact. Whether these interesting endomorphic and exomorphic changes are to be accounted for on the basis of assimilation of some of the country rock during the intrusion of the gabbro, or on the basis of the action of vapors from the intrusive, it at least appears quite certain that the gabbro must have been considerably superheated in order to have so notably affected the granite. As judged by the mode of occurrence of the gabbro stock, the stoping hypothesis recently advocated by Daly or the hypothesis of marginal assimila- tion might be applied to account for the more acidic border phase of the gabbro, but the sharp contact of the gabbro against'the granite would seem to preclude the possibility of accounting for the more basic contact zones of the country rock on the basis of actual assimi- lation of some of the granite by the gabbro. Ba 2) _ NEW YORK STATE MUSEUM PEGMATITE The most interesting thing about the pegmatite is its distribute b because it is very commonly directly associated with the gabbro | masses. Many times the pegmatite, in the form of dikes or veins, may be seen cutting the gabbro (see plate 4) and hence the younger — age of the pegmatite. This direct association of the very acid © pegmatite with basic gabbro and its age intermediate between the — basic intrusives — gabbro and diabase — are rather anomalous fea- — tures for which the writer can offer no explanation. ; Among other places where pegmatite may be seen cutting the gabbro are: (1) at the top of Hackensack mountain; (2) 1%4 miles — south-southeast of Potter mountain; (3) 114 miles a little east of — north of The Glen; (4) 1 mile south-southeast of The Glen; (5) 144 miles northeast of Pottersville; (6) 124 miles southeast of Ches- tertown; (7) 2% miles southeast of Chestertown; and (8) 2347 miles south-southeast of Chestertown. At most of these places the gabbro is shot through with small pegmatite veins. At the fourth named locality one dike is 50 feet long and 25 feet wide and very rich in big orthoclase and albite feldspar crystals. At the seventh — named locality a small pegmatite dike contains fine crystals of biotite muscovite and black tourmaline. At the sixth and eighth named localities there are pegmatite dikes 50 to 100 feet long with books of muscovite up to 5 or 6 inches across at the eighth locality. Large pegmatite dikes are not common away from the gabbro, there being but two examples worthy of mention namely: just east of the old garnet mine south of Daggett pond where there are many — poorly formed black tourmaline crystals up to 6 inches long, and one-— quarter of a mile above the mouth of Mill creek where there is a_ dike 200 feet long and 4o feet wide in granitic syenite. q DIABASE Mode of occurrence and distribution . In striking contrast with the neighboring gabbro, the diabase invariably occurs in typical dikes which have clearly broken through narrow fissures in the country rock. They vary in length from — 20 or 30 feet to 200 yards, and in width from 5% inches to 40 feet | The chief features of occurrence are brought out in the follow ng base of Heath mountain or 3 miles cen northwest of Warrensbilil This dike has a maximum width of 40 feet and a length of 200° ‘yards. It is fine to medium grained toward the interior and very GEOLOGY OF THE NORTH CREEK QUADRANGLE 39 fine grained along the borders. It breaks through both Grenville and granite gneisses and the contactsareeverywhere perfectly sharp, there being no evidence whatever of contact metamorphism. A num- ber of small tongues, from 1 inch to 3 or 4 feet wide, branch off the large dike and extend as much as 25 or 30 feet into the country rock. One of these branches cuts a pegmatite dike and another cuts Grenville limestone. This large dike strikes across the folia- tion almost at right angles. One and one-half miles southeast of Johnsburg a diabase dike, 2% feet wide and 60 feet long, cuts Grenville quartzite parallel to the foliation. All of this rock is fine grained but exceptionally so at the contacts, and on one side an inch wide zone of basaltic glass or obsidian is perfectly developed with some very small tongues of glass extending into the country rock. A typical diabase dike 4 feet wide cuts the gabbro stock three- quarters of a mile south of Warner pond. The dike has fine grained borders, sharp contacts against the gabbro, and is clearly traceable for 150 feet or more. In all eleven diabase dikes were found, being well scattered over the quadrangle. Most of them cut across the foliation of the coun- try rock at high angles, thus differing from the gabbros, and they probably have been forced up along joint planes. In nine of the eleven occurrences the dikes strike northeast and southwest which is quite the rule for such dikes in the eastern Adirondacks. So far as can be determined, these dikes all come up vertically through the country rock. Megascopic and microscopic features The diabase is a very dark bluish gray to almost black rock which, in all exposures, is hard and fresh except for the immediate surface which is often weathered to reddish brown. The granularity and texture vary from glassy to very fine grained to medium grained diabasic, the finer grained rock being wholly confined to the borders and the diabasic texture nearly always being just visible to the naked eye in the typical medium grained rock. Except for the above named differences the diabase shows no facies whatever visible to the naked eye, and this again is in marked con- trast with the gabbros. The diabase is wholly devoid of any meta- morphism and inclusions of country rock are never found. The only minerals recognizable by the naked eye are the tiny feldspar laths and an occasional pyrite speck. AO NEW YORK STATE MUSEUM The whole range in mineralogical composition is brought out in the following table: TABLE 9 Mineralogical composition of the diabase . Andesi £ Gl Slide to ee Augite Biotite | Ilmenite e arene Quartz = dorite Ay mass ne I 8 47 25 | 22'.5 4 d/| Dt ee little | little oy \. | 6 | littles|) eee 2 | little 2 48 55 | Mostly chlorite 40 or Bud ics ele little | little 3 7. 55 | Mostly chlorite. } | many 4 10 5 Blt cane SPECKS Hess. 85. | tach eee . 5 9 | 55. i fho| ae aeiegeee 5 | little 25 Tl ae | The remarkable similarity in composition is a striking feature. Nos. I, 2, and 3 are typical holocrystalline diabases from widely separated dikes. Nos. 4 and 5 represent finer grained or border phases and have more or less glassy ground mass. No. 5 presents a striking appearance under the microscope because the feldspar ~ crystals which are incipient and almost indeterminate tend toward © | sheaflike bundles (see plate 6, lower figure). : Number 1 of table 9, which may be regarded as typical of all the | diabases, is from the large dike (above described) at the base of — Heath mountain. The fine to medium grained rock shows an excel- — lent diabasic texture visible even to the naked eye. Judging by the extinction angles, the broad laths of somewhat decomposed plagio- — clase range from andesine to labradorite in composition. Pale red- dish brown augite, in stout prisms, shows a very faint pleochroism. It exhibits good cleavage and sometimes good crystal boundaries. The biotite is much changed to chlorite and stained with black iron oxid. The ilmenite often shows transition to leucoxene. Apatite occurs in tiny needles, and pyrite and quartz in small irregular grains, the latter being probably of secondary origin. Chemical composition, norm, and mode The diabase from the dike at the western base of Heath moun- tain has been analyzed for the writer by Prof. E. W. Morley. aly GEOLOGY OF THE NORTH CREEK QUADRANGLE Al TABLE 10 | Chemical composition and norm of diabase 4 ' | | 5 | | bh tr) a be | 5 $ Ce ws) e = s ~ Ae} oS & ES g a ee te) ye. | 6 | a le ve el) eS SiO. 50.57 | .843 . _... {120 276 |134 126 |153 34 Aba... ee fe ee 20 NG ABs (OZ. te ORAS, Cet FeO; eee! (020 |....|.¥-. We ibe Zo tanlh an taeh ke od 1 Re eae ae, Or FeO: .... 10.09 MMM ASEH Scared A citeslm ee ds >| = <- 20, | 26-|. 63 migo..... 4.98 2 a ed B70 ae a a 7 67 137 ey re Sie es ee oe) ig Nee a 67 ee eee eae Na.O 2 .Q2 047 Dee Ge re ioe call a OMI ie NV Rt soll fo a 1/89 | .020 : Pte. OR Aae ey) | 2.) ate aes amen H.O+ Ou a oa =i) ty 2)| > uae er aco | her oes oneaneta Peace See |) aca H:0— Oe ae meee PRE EP re he tibet bie = Tiere. 3 2s 2 Gill Pare el ates ieee ees (aries oa We Meade wadl ec: thet. PeOb i 3. UIST a (iaece>. 8 Ve omer | (nee aR te a eee | eee CT eeu .09 eee Me eMac Heyl a 6 fie iets es [a ble [a aon | ae a ee .09 O05 j.---| Ty 4 [.---fe-.-fee-- pe tok ee er Ce MaQ..... | UG A Oe SASSI RING Ge | ll ie eats cath 5 Co ae a OGM Goh. ay Seca ot boys oT > ae ia esibeaes ieee srl. SNRs 3 ails belo 8 Pare ny a) pared Pees ae ae eee ye oe ee ee ko A eae ea hs AS Sg Se LOS tea ane: Puemeal.: . 00 .78 , | | oat |. 560.0F 5 3 8 ae 2.04} (Class, = <—>—=III, Salfemane COPCR ee. 11.12 Rent" 42.34, 2.5 fe, eo 24.10 { Sal.= 56.01 Anor 18.63 Ob 7-20" NaG@ie...... ae. Order, a = te 5, Gallare Wien, °°. 4.64 ) K.0!+Na;,0! OF Si 5s a 5.02 Rang, — —— =— <->-=3, Camptonase Wb eas... .67 CaO! Sy ee "aaa Gor. .:..:.. .16 Fem.= 42.34 Diop 14.44 ie 8 ee. 6 ie mypet....... 17 4r Subrang, = —<->-—=4, Camptonose Petes... 1.13) Na:O! 47 5. 7 MALS... 99.48 TABLE II Mode of diabase poem Shee | SG) ay wou: | weigues’ Plagioclase......... 2 027 46.88 2.66 5 392 40.78 Merge. ............ 975 22.55 3.20 3 120 23.59 MeeMOMT@ 0. aes: 168 3.88 aby 868 6.56 a I ogo 25.21 4.40 3 507 27.20 MG. ke 30 .69 5.00 150 1.13 MC sss ss 26 .60 2.65 69 .52 De 8 18 3.20 26 .19 4 324 ES 13 222 99.97 :e* 42 NEW YORK STATE MUSEUM Thus, according to the old qualitative classification, the rock is a biotite-diabase, while under the new quantitative chemical classifica- tion it is a biotite-camptonose. The amounts of SiO,, Al,O,, and CaO in the analysis strongly bear out the determination of the plagioclase as ranging from andesine to labradorite. Such a high content of FeO in the analysis makes it certain that the biotite is rich in ferrous iron, since there is not enough magnetite and augite - to account for so much FeO. The sulphur appears too low as judged © by the amount of pyrite visible even to the naked eye. The high TiO, shows either ilmenite or that the magnetite is decidedly titan- iferous, though a little of the TiO, may be in the biotite. The low Fe,O, content in the analysis favors the presence of ilmenite. | It is important to note that the analyses of the diabase and typical gabbro are very similar except for somewhat higher silica and lower lime in the diabase, this difference probably being due to the slightly more acid character of the plagioclase in the diabase. Thus the two rocks have quite certainly been derived from the same source of basic supply though at different times. —— ee ee ee ee ee ee ee TABLE I2 Adirondack diabase analyses compared ee ee I 2 Re 4 5 6 SO oer ies aos Mee aod 5OnS7 4. 4a ons 44.51 45-46 | 46.73 50.89 J ALO POR So Me tae ae 13.58 19.42 19.99 19.94 16.66 15.39 Ress eee a 3.26 5.72 3.56 | Fateh aa Wa Mp 10.09 6160) ||| eo a a 36 8.45. 51h 1S CRE In CNET 4.98 5.98 8.11 2.95 8.12 7.605 AG) 50s s See hs nee Tori Orr 8.15 842 8.03 8.7505 - IAG aera eat ea 292 4.39 5.24 212 2575 5.67. RUD) 2 oe Ber see ts cao 1.89 47 2.60 Bo 1.64 2. 72g (5 ES gad iat eee 1.10 3.00 2208 2, 30 2.39 2.465 dS), AR era ee 2.68 25 |). | .03 | .. ea -_ 1a @ MRR Fame tees aaa SDB A 5, a sue ule ete eal .39 | .-. can OSES Cosy ni eee te OQ ola gic bien tl he eee ee 18 |... Name tent Ag a ead a $09. pc A sotcs 2) || leony | ee 26 |... OO acai ccaleen meee MLE tally sabe es || Mere es asl icon ee 06 WO. < Soh elemenee es oe 286: |\ Samal) ee hace trace an. Oy Se ee ee FOO ia): esac ore yas Guay oe eee 04 r 01 © BAM d af Soe a -TO | sees | cee ee || eee = ce rr ee (03 dese cee |e eee | Se eer , OO PIM ae ULC moa bo PR ony 2.00 | 26. .06 |e ee ere t | | | EE _ 99.78 | 100.54 | 98.75 | 99.66 | 100.27 99.25 GEOLOGY OF THE NORTH CREEK QUADRANGLE 43 1 From western base of Heath mountain, North Creek sheet, Warren county. Analyst Morley. 2 From summit of Mt Marcy, Essex county. Analyst Leeds. N. Y. State Mus. 30th Annual Rep’t, p. 102. 3 From shore of Upper Chateaugay lake, Clinton county. Analyst Eakle. Amer. Geol. July 1893, p. 35. 4 From Palmer Hill, Black Brook township, Clinton county. Analyst eee U. 5. Geol. Surv. Bul. 107, p. 26. 5 From Bellmont township, Franklin county, dike 13. Analyst Morley. N. Y. State Geol. 18th Annual Rep’t, p. 120. 6 From shore of Upper Chateaugay lake, Clinton county. Analyst Eakle. os. ti. p. 35. The North Creek sheet diabase (no. 1) is lower in Al,O, and CaO, and higher in TiO, than any of the others. It is also some- what more acid than usual for the diabases, due to the more acid character of the plagioclase feldspar. Lack of variation of the diabase Because of its remarkable homogeneity in composition, the dia- base presents a marked contrast to the neighboring gabbro. The diabase never contains inclusions and, with a single very local ex- ception below described, never shows any evidence of magmatic assimilation even in the largest masses. This difference is quite certainly due to the difference in the mode and condition of intru- sion, the diabase having clearly been forced through comparatively narrow fissures in the country rock and near the earth’s surface as the texture shows. In such intrusions magmatic stoping would be reduced to a minimum or absent. Contact phenomena A small dike, 5% inches wide, which cuts the Grenville limestone at the asbestos mine three-quarters of a mile southeast of Thur- man, shows contact phenomena which deserve special mention. Fol- lowing is a description based upon thin sections and hand specimens (see plate 7). Zone 1 This is typical, unaltered, medium grained, greenish gray, serpentine marble. Zone 2 This zone, about one-third of an inch wide, lies along the contact with the diabase. It consists of a fine grained, dark green, well-baked serpentine marble. Zone 3 One-sixth of an inch wide. Nearly black (greenish gray in thin section), glassy looking dike rock which shows an irreg- ular but sharp boundary against the marble. It appears to consist ye NEW YORK STATE MUSEUM largely of rather homogeneous, serpentinous material (bluish gray interference tints) which is apparently igneous glass into which ser- pentine marble has been fused. Occasional well-formed laths of — plagioclase and many specks of magnetite occur. The outer I or 2 millimeters of this zone are very rich in magnetite specks. This zone shows a rapid transition into the next one. : Zone 4 One-third of an inch wide. Reddish brown, glassy lool ing. Apparently good igneous glass filled with many tiny specks of what seem to be magnetite and perhaps Io per cent of plagioclase mostly in laths but some in stout prisms with distinct zonal struc- ture. This grades perfectly into the next zone. Zone 5 One-half of an inch wide. Pale green color and much like no. 4 except for absence of the tiny specks. The green color is due to serpentinous material which appears to have been absorbed iH by the molten mass. The contact between this and the next zone is rugged though pretty sharp. t Zone 6 Ordinary bluish black diabase from within the dike and — with no serpentinous admixture. This rock is mostly a dark glass which contains 5 per cent plagioclase laths and 5 per cent pale red- 1 dish brown, euhedral augite crystals and numerous specks of pre- sumably magnetite. . f a | x x) | f PALEOZOIC OUTLIERS No actual outcrop of Paleozoic strata has been found within the borders of the quadrangle, but certain nearby Paleozoic outliers have an important bearing upon the geologic history of the regiaa Two of these outliers have been described by Professor Kemp, ¢ one of them being Little Falls dolomite which occurs at Schroon Lake e village (Schroon Lake sheet), and the other being Potsdam sand- stone which occurs near the village of North River Set Lake sheet). | During the summer of 1910 the writer discovered a small oul zoic outlier 1 mile south of the map edge and 1 mile due west of High Street village (Luzerne sheet). The exposures are rather poor and small but the rock is quite certainly in place with the strata lying in nearly horizontal position. Both sandstone and dolomite beds occur and it is not certain whether the rocks represent the pas- sage beds of the Theresa formation or the contact between the Pots- dam and the Little Falls dolomite, though the former is more prob- able. This outlier lies at 1400 feet elevation and not far to the west of the No. 9 mountain fault and on its downthrow side. t { GEOLOGY OF THE NORTH CREEK QUADRANGLE 45 The important outlier at Wells (Lake Pleasant sheet), which shows rocks from Potsdam to Canajoharie, has been known since the early days of the State Survey. The nearby occurrences of Little Falls dolomite along the southern portion of Lake George should also be mentioned. | Within the map limits, certain drift boulders are significant as showing proximity to concealed outcrops or ledges which were scraped off by ice erosion. Thus a fragment of Potsdam sandstone 2 feet across and very angular was seen just east of the old garnet mine near Daggett pond, and many Potsdam fragments up to 1 foot across occur in the river valley bottom between Moon and Heath mountains. The occurrences of early Paleozoic marine strata on all sides of the North Creek quadrangle furnish practically conclusive evidence that much, if not all, of the area of the quadrangle was covered by that early Paleozoic sea. Thus the Potsdam (upper Cambric) sea, which encroached over northern New York from the north- east, must have swept over the North Creek region and this was quite certainly succeeded by the Theresa and Little Falls seas. Regarding the presence or absence of the Ordovician sea, we have no positive knowledge, though the Wells outlier suggests that it, too, was present. It is well known that when the Potsdam sea encroached upon the eastern Adirondacks, the region was greatly worn down to the con- dition of nearly a peneplain. Since some portions stood out above the general level of the peneplain, it is quite possible that the Pots- dam sea, and even the later Cambric, did not cover the higher por- tions as Professor Kemp has suggested. At any rate the evidence is strong that very much if not all of the North Creek area was covered by the late Cambric sea and probably also by the Ordovician sea. The deposits made in those seas have all been removed by erosion except for the small outlying masses above described. It is important to note that each one of these outliers has been very con- siderably faulted downward from the original position of the strata and thus they have been protected against complete removal by ero- sion during so many million years. STRUCTURAL FEATURES FAULTS General considerations. That the eastern Adirondacks are ex- tensively faulted has been recognized for some years, but thus far comparatively little attention has been paid to the detailed study es - NEW YORK STATE MUSEUM and mapping of these faults well within the Precambric area. The North Creek quadrangle, which lies in the midst of this eastern Adirondack faulted region, is literally cut to pieces by faults. On) the accompanying geologic map the writer has indicated the posi- tions of over forty faults, most of which show unmistakable evi-- dences of their presence, while the others, shown on the map by the heavy broken lines, are more or less certainly present. | The faults are all of the normal type with fault planes vertical ” or very steep. Because of the character and structure of the rock | masses and the lack of any well-defined stratigraphic relations, it is practically impossible to determine the actual amounts of dis- placement, though in many cases minimum approximations can be) made. Such minimum figures commonly range from a few hundred | to a thousand feet or more. One feature worthy of special mention is the frequent rapid diminution of throw within very short dis- 7 tances. Thus in many respects the North Creek faults are much) like those of the Mohawk and Champlain valleys, which is to be expected as the faults of this whole eastern Adirondack region were all produced at the same time or times. With regard to the strike, however, the North Creek faults are rather exceptional because the general trend of the Adirondack faults is north-northeast by south- southwest, while within the North Creek quadrangle this trend 1 the rule only in its northern portion. Asa rule, faults within the Precambric area are difficult to locate and trace with any great degree of accuracy and certainty because of the general similarity of the rocks and the lack of ordinary fos-" siliferous strata. In the North Creek region, however, the condi- tions are particularly favorable for locating faults both because of the unusual excellence of exposures and the large amount of widel ry distributed weak Grenville strata. . Frequently the line of contact between the syenite or granite and the Grenville is very regular and sharp, the Grenville often ccna to dip under the igneous rock with the latter rising abruptly an to a great height above the Grenville. Among the best examples ¢ of such phenomenon are the southern sides of Huckleberry, Crane, ane Little mountains, and the western sides of Oven, Prospect, Bi and Potter mountains. There are only two possible explana of this phenomenon, namely, either that the igneous rocks were truded into the positions which they now occupy or that faulting has occurred. If this is to be explained simply on the basis of in trusion, then we are forced to assume a remarkably irregular surface ‘= Se oe Fo ir Porphy. i Tiwi i c G - = PE TGrarute ’ bes ¥ -_ le i€ as 4 " os 4 ; Diabase Atal sca bmee Mor) ry <—_- | e at AY TR URN TORE en Grenville Syenite [Xz] Granite porphyry [ H | Diabase . ° . o 45, Horizontal scale *$—-=-=——+ Vertical scale ——7->-,-—* Yi x* x xv Fig. 5-8. Structure sections across the North Creek quadrangle. The position of the section lines is shown on the geologic map. 4 eh aie Cees lore = ~eeresrete cpeee peaere sarammartgerireeaeme 0 6 EE SE ES ap ee eee == - SE EE eee ees A ee “ie p-% a ee ee en ee GEOLOGY OF THE NORTH CREEK QUADRANGLE 47 of the newly cooled magma and also that the molten masses, in all these cases, broke through the Grenville along very straight or regu- lar lines often for miles. Both of these assumptions are out of harmony with well-known observations in other regions. The very common dip of the Grenville downward against the faults is due to the fact that most of the prominent fault scarps face the west while the prevailing dip of the Grenville is toward the east. Among the more positive criteria for the recognition of the faults are the following: (1) actual steep to vertical scarps, often in hard, perfectly homogeneous rock, and frequently in such positions as to preclude the possibility of their having been formed by ice or stream — erosion; (2) the distinct tilting of the earth blocks gradually down- ward away from the scarps; (3) the frequent presence of actual crushed, sheared, or brecciated fault zones; and (4) the long, straight contact lines between the Grenville and the igneous rocks, with the latter rising abruptly high above the former. What is the age of the faulting? That some, at least, occurred during Precambric time has been pretty well established but, so tar as known, such faults are of minor importance and certainly have no appreciable influence upon existing topography. But a single case of such very ancient faulting has come under the writer’s notice within the area of the quadrangle and this occurs along the road three-fifths of a mile southwest of Sullivan pond. A fault, plainly visible for 12 feet, there passes across a glaciated ledge of quartz syenite. On the east side, for a width of 7 or 8 feet, the whole mass is a fault breccia. This breccia is fine at the fault and coarser, with fragments up to 1% feet across, away from the fault. The fault strikes north 30° east and is in no way related to existing topography. There is good reason to think that considerable faulting occurred during the Paleozoic era after the deposition of the Ordovicic sedi- ments because rocks of that age are involved in the faulting along the eastern and southern borders of the Adirondacks. Cushing has suggested that the faulting may have been initiated at the time of the Taconic revolution when the rocks immediately eastward were so greatly disturbed, but he says:' ‘ The great earth disturbance (Appalachian revolution) which prevailed in the Appalachian zone toward the close of the Paleozoic would seem more likely to have brought about the major faulting of the region.” We know that IN, Y, State Mus, Bul, 95, p. 405. 48 NEW YORK STATE MUSEUM the whole State was then upraised practically without folding, and ( the conditions were certainly favorable for extensive fracturing of the strata. | . Any fault scarps or ridges produced during or at the close of the Paleozoic must have been quite or nearly obliterated during the long Mesozoic period of erosion. If so, how do we account for the 4 present Adirondack ridges which follow fault lines? As a result of — the uplift of the Cretacic peneplain one or both of the following . things happened, namely, either that there was renewed faulting or that, as a result of unequal erosion (due to differences in rock ~ character) on opposite sides of the faults, the old fault scarps were — renewed. It is quite certain that both things occurred and thus” we account for the present Adirondack fault ridges. That some ~ of the faulting actually dates from the uplift of the Cretacic pene- plain, or possibly even later, is proved by the existerice of certain — fault cliffs in perfectly homogeneous rock masses, and by the fact | that many of the tilted fault blocks have been little modified by © erosion since their formation. Among many good examples of fault — scarps in homogeneous rocks are those on the west sides of Moon, . Kelm, and Chase mountains, while tilted fault blocks little affected ~ by erosion are those of Moon, Birch, Crane and Huckleberry ~ mountains. — Little-Crane-Huckleberry mountain faults. The structural rela- ~ tions shown by these three mountain masses are truly remarkable ; and the faults are the most interesting within the quadrangle. The & deep, narrow rift between Huckleberry and Crane mountains was carefully examined and, judging by the frequency of outcrops, it is) 4 : quite certain that a narrow belt of Grenville separates the mountain masses as shown on the map. A narrow valley of Grenville, chiefly limestone, with almost continuous outcrops separates Crane moun- 4 tain from the granite ridge just south. Likewise there is a valley of fi Grenville, chiefly limestone, immediately to the south of the granite ridge (Little mountain and its westward extension). ] In each case the mountain mass of igneous rock presents a high and very steep to almost precipitous wallon the south side, and in each case the belt of Grenville comes abruptly against the igneous rock wall. ‘ Per. F iv. ( \ ; i 7 : . : ’ * 4 y . i f : *, ® _ ‘ % Re ? t s 7a 4 k i f , % i ‘ re go 4 ay i sat = ee i ee GEOLOGY OF THE NORTH CREEK QUADRANGLE 53 strikes. The usual evidences prove the faulting, the eastward downtilt of the fault block being especially well shown. Neither of the two faults just described has a maximum displacement of more than a few hundred feet. Brant lake faults. A very prominent fault, which may be called the Brant lake fault, passes along the northern side of the lake of the same name within the adjoining Bolton sheet. The lake clearly ‘occupies a depression at the base of this fault scarp.. Only the western end of this fault comes into the North Creek quadrangle where it passes along the southern base of the mountain at the village of Horicon. It can not be traced across the Schroon river. Near the village of Horicon distinctly sheared and slickensided rock may be seen in the granite quarry. At the village the displacement appears to be no less than 400 or 500 feet. On the south side of the narrow valley at Horicon a smaller fault, parallel to the larger one, is clearly indicated by a crushed zone in the granitic syenite. The eastward extent of this fault is not known. Chestertown faults. A prominent fault with northwest-south- east strike lies along the southwestern base of Prospect mountain and is thought to be continuous with the fault shown on the map just east of Loon lake. These two are certainly exactly in line and, though they have not been positively connected, they will be regarded as parts of the same line of fracture. At the Loon lake end the fault shows an almost vertical scarp 300 feet high where it passes along the western border of the gabbro stock. The scarp there consists of badly sheared gabbro, and Grenville limestone dips directly against the base of the scarp. The southwestern side of Prospect mountain is a fine example of a high, steep fault scarp with banded Grenville gneisses dipping eastward against the base of the mountain which consists of a granitelike mass of gneiss. A displacement of no less than 700 feet is shown here. The southern end of the fault is marked by a rather steep scarp several hundred feet high and in the homogeneous granite porphyry. There is fairly good reason to think that another fault with north-south strike passes through the western edge of the village of Chestertown, but since its presence is not certain it is represented on the map by a broken line. The fairly prominent scarp which forms a long straight boundary between the Grenville and the igneous rocks is the chief evidence for considering a fault here. The fault plane is mostly concealed by heavy drift. 54 NEW YORK STATE MUSEUM j ; -z The Glen-Riparius fault. This fault, whose length is some 8 or g miles, is clearly the longest one lying wholly within the quad-— rangle. It is topographically very plainly marked, a whole line of low mountain peaks forming the crest of the scarp. This great fault block shows a very distinct downtilt toward the east which accounts for the peculiar drainage condition because no considerable streams enter the Hudson river from the east along the line of the — fault but, instead, the streams all drain from the crest of the scarp down the eastward slope and into the Friends and Loon lake © basins. The Hudson river itself has had its course determined f along the base of the scarp. A displacement of from 300 to 600 q feet is commonly shown. { Gage-Stockton mountain fault. As shown on the map by the — heavy broken line, a prominent fault is thought to extend along the eastern bases of Mill, Stockton, and Gage mountains and south- — ward to The Glen. The principal evidences for faulting here are i ) the arrangement of the high, steep mountains along a regular line © and the long, smooth contact between the areas of Grenville and mixed gneisses and the igneous rocks. The usual tilted character of the fault blocks is here not shown. Shear zones were not noted © though this is of little significance because exposures on the line of the fault are very scarce. The displacement of this fault appears to be as much as 800 or 1000 feet. | a If this fault is actually present, then the large wedge of Grenville — and mixed gneisses in the valley bottom is of the nature of a © through fault block. 4 Oven-Mill mountain faults. These faults are most likely parts — of the same line of fracture, though the connection has not been positively traced. In each case Grenville (chiefly limestone) dips eastward and directly against the base of the mountain. The Ove n mountain fault scarp, which rises nearly goo feet and is very steep . to almost precipitous, is an impressive sight as viewed from the west. An eastward downtilt of the block is fairly well shown. The 7 ) ¥ \ ; —— | A awl ge > oi ee pee aces Mill mountain scarp is not so steep but rises to a height of over 700 feet. Because of the much weaker Grenville between the two ~ mountains, no distinct fault scarp is there present. | North Creek fault and branch. This prominent fault strikes | north-northeast by south-southwest and passes through the village — of North Creek. Northward from the village it is very clearly traceable as a topographic feature for at least 10 or 12 miles and — well into the Schroon lake quadrangle along the west side of the Plate 10 Mou W. J. Miller, photo View across the Hudson river from a point just south of the railroad station at Riverside, and typical of the region through which the river flows. The mountain consists of quartz-syenite. The Glen-Riparius fault, which the river follows for some miles, lies along the base of this mountain. i +] Na a PESO —_ Se GEOLOGY OF THE NORTH CREEK QUADRANGLE 55 valley of Minerva stream. From North Creek to the map edge the line of the fault is marked by a distinct depression which has been formed along the belt of weakness. Except near the Hudson tiver where the weak Grenville is crossed by the fault, a well- define’ fault scarp forms the upthrow side on the west and it is important to note that this scarp strikes at a high angle across the foliation of the rocks, thus proving the independence of the fault and toliation planes. One and one-fourth miles north of North Creek decomposed and somewhat crushed granite marks the passage of the fault. Just at the map edge the eastern face of the Moxham mountain mass is a fine illustration of a steep fault scarp rising to a height of goo feet. Since the fault here passes through a great ‘mass of rather homogeneous, igneous rock, it is certain that the amount of displacement is not less than 1000 feet. An interesting feature is the large inclusion of Grenville gneiss just south of Moxham mountain; it occupies such an unusual position because it lies on the upthrow side of the fault in a place fairly well pro- tected from erosion. In the stone quarry just east of the main fault and near the map edge, a fault plane with breccia is clearly exposed in both walls of the quarry. Its strike is north 30° east and it appears to be a minor fracture parallel to the larger one. At the map edge a fault branches off the main tine of fracture and follows the steep mountain side to Fuller pond. Just east of the pond the scarp of Grenville gneiss rises almost vertically for several hundred feet. South of the village the North Creek fault is clearly traceable by the steep mountain sides of igneous rock against which the Grenville comes in contact along a straight or at least very regular line as far south as Baker’s Mills (Thirteenth Lake sheet). Holcombville fault. There is considerable evidence for a fault with a northwest-southeast strike along a nearly straight line pass- ing through the village of Holcombville. It is represented by a broken line on the map because its presence is not regarded as con- clusive. It is thought to extend for some miles into the Thirteenth Lake quadrangle or nearly to the village of North River. The chief evidences for faulting are the long, straight contacts of the Gren- ville against the bases of the high Oven mountain mass of igneous rock and the great mass of syenite within the Thirteenth Lake sheet. No shear zones were noted and the usual steep scarp and the tilted character of the fault block are absent. 56 : NEW YORK STATE MUSEUM ~ Collins brook fault. The Collins brook fault lies nearly parallel to the Holcombville fault and it is named from the small brook which follows the base of the scarp near its north end. It is clearly — marked by the topography for a distance of 5 miles between the © Hudson river and Mill creek near Wevertown. The evidence for its existence is threefold, namely: (1) the long, regular scarp of granite whose crest is lined with peaks rising from 300: to 600 feet above the base of the scarp; (2) the long, smooth contact of the Grenville against the base of the scarp; and (3) the distinctly eastward downslope of the earth block away from the crest of the scarp. | Henderson mountain faults. The principal fault of this group — strikes northeast-southwest along the western base of the Hender- — son mountain mass. Its position is plainly marked by the topog- — raphy, and though the scarp is not as steep as usual, it is neverthe- — less very prominent and straight and cuts across the foliation of the rocks at a high angle. The sharp swing of the Hudson river northeastward for 144 miles along the line of the fault has been determined by the crushed belt of weakness. North of the river the position of the stream which flows through Bird — pond has also been determined by the fault. As judged by the height of the scarp at the south end and also at the base of Hender- — son mountain, the displacement is fully 700 feet. Where the fault — crosses the belt of mixed gneisses the scarp is much less prominent — because of the relative weakness of. the rocks there. No tilting of © this fault block is noticeable. This fault certainly continues for some 3 miles northward into the Schroon Lake quadrangle along the | ») western bases of Green and Pine hills. The second fault of this group strikes almost parallel to the — _ Henderson mountain fault and lies at the eastern foot of the moun- — tain whose elevation is 1915 feet. The very steep side of this — mountain rises 700 feet and is another good example of a faulty | scarp wholly within homogeneous rock. Where the fault passes | into the area of weaker mixed gneisses the scarp is much less prominent. > The third fault of this group is a small one which lies south of Igerna and along the north side of the Hudson river. It is” wholly within the area of mixed gneisses but at some places linden i : vertical scarps rise fully 200 feet. : | Schroon lake faults. The larger of the two faults here de- — scribed strikes northeast-southwest and extends along the eastern — GEOLOGY OF THE NORTH CREEK QUADRANGLE 57 side of the south end of Schroon lake and thence southward to the north end of Loon lake. At two places along Schroon lake the fairly steep scarp rises fully 400 feet. The southern end of the fault block is a mass of Grenville (chiefly quartzite) whose bold scarp at one place rises 4oo feet. The whole fault block, especially the southern part, shows the usual downslope toward the east. This scarp strikes at a high angle across the foliation bands and: hence it is difficult to account for except on the basis of faulting. A smaller fault along the western side of the southern end of Schroon lake has a prominent scarp rising some 300 to 400 feet. Where it cuts across the gabbro stock near the map edge the fault scarp rises as a high vertical wall along which the rock is unusually soft and weathered and evidently sheared. Loon Lake mountain fault. The short fault shown on the map just east of the north end of Loon lake-and at the base of Loon Lake mountain is one of special interest. Here again the contours are not close enough together since the fault scarp which rises to a height of 700 feet is very steep, the upper 300 or 400 feet being a sheer precipice. We have here at once the highest steep ledge of Grenville and the finest example of a practically unaltered fault cliff within the quadrangle (see plate 10). The upper portion of the cliff consists of quartzite in thin to thick beds with low north- easterly dip so that the truncated edges of the quartzite layers are distinctly visible in the face of the cliff. The less steep scarp forming the western face of this fault block as well as its down- tilt toward the east are due to the Schroon lake fault already de- scribed. Plate 11 gives a good-idea of the appearance of this fault block mountain. | Other faults. The small fault north of Valentine pond strikes ~ due north and south and shows a prominent scarp near its north end. The contours are not close enough together on the mountain side since the wall of rock, which rises fully 600 feet, is very steep to actually vertical in places. Hard, distinctly banded Grenville gneiss makes up the upper three-fourths of the wall and rests upon granite. The fault has broken sharply across the strike of the foliation of both the Grenville and granite. As judged wholly by the topography, there appears to be a con- siderable fault block just west of Loon lake. The fault and its scarp lie from 1 to 1% miles west of the lake and the downtilt toward the lake is very noticeable. The shape of the lake basin and character of the topography suggest the presence of a fault along the west side of Friends lake. 53 | NEW YORK STATE MUSEUM As shown on the map, short faults are suggested at the eastern base of Mill mountain, the western base of Stockton mountain, and the northern base of Wolf pond mountain. Except for some evi- dence of shearing on the side of Stockton mountain, the only evi- dence for these faults is topographic, it being difficult to account for these steep scarps except on the basis of faulting. The writer believes it quite likely that other, chiefly minor, faults occur within the quadrangle, but the ones above described are the only ones he feels justified in representing on the geologic map as actually or very probably present. | FOLIATION All the rocks except the diabase and pegmatite show more or less of the foliated structure. It is best seen in the Grenville gneisses which are commonly distinctly banded due to differences in the composition of the beds, the foliation so far as observed always being parallel to the bedding. The syenite, granite, and granite porphyry are always gneissoid but never distinctly banded, the structure being accentuated by a drawing or flattening out of the dark colored minerals parallel to the foliation. The more basic pyroxene and hornblende syenites are, as a rule, not very gneissoid, as, for example, the Bull Rock mountain syenite. In fact it may be — stated as a very general rule that the more basic, even and medium 4 grained rocks of the syenite-granite series are least gneissoid; while the more acid rocks carrying hornblende and some biotite are clearly gneissoid; and the most acid rocks rich in quartz and biotite are very gneissoid. In these last named rocks the very © presence of biotite flakes and the tendency of the quartz to be- — come flattened favor the development of the foliated structure. - Again, it often happens that when members of the great intrusive series, especially the granites, are close to the Grenville the rocks are more gneissoid. Thus, at the top of Heath mountain the pink 4 granite is rather poorly gneissoid while at the base of the mountain 3 it is very gneissoid. a The typical basic gabbro stocks seldom show a gneissoid struc-— ! ture except rather often in the narrow amphibolite borders. Some of the more acid stocks are clearly gneissoid. An interesting feature is the common occurrence of rapid changes — | in degree of foliation even within the same rock ledge. Thus, just west of The Glen (on the mountain side) there are big ledges of Gein agse my Plate 11 W. J. Miller, photo The Loon Lake mountain fault-block, as viewed from a point three- fourths of a mile to the south-southwest. On the left (west) side the steep slope is that scarp of the larger of the two Schroon lake faults. The down-tilt of the block toward the east is perfectly shown. The cliff, several hundred feet high, which faces the south, is the scarp of the fault along the south side of the mountain. The upper portion of this mountain, which rises 600 feet above the valley, consists of Grenville quartzite and its lower portion of biotite-garnet gneiss. ape Se 5 SE. eee GEOLOGY OF THE NORTH CREEK QUADRANCLE 59 hornblende granite. At times the rock is pinkish gray, medium to coarse grained, and not very gneissoid; while again, and by rapid changes, the rock is gray, fine grained, and very gneissoid to al- most schistose. Both rock types have the same composition and both show signs of granulation, but the latter rock especially so. One of these clearly does not cut the other, but rather there is a rapid gradation from one to the other parallel to the foliation, and it seems clear that the fine grained, very gneissoid rocks were produced along belts of shearing perhaps at the time of the de- velopment of the foliation. Such a rapid transition from fine to medium grained granite is also well shown even in a hand speci- men from the summit of Oven mountain. Many dip and strike observations on the foliation were made, the more representative ones being plotted on the accompanying map. Strike observations can generally be made with a fair degree of accuracy, but dips can seldom be determined to nearer than 5 or 10 degrees. The amount of dip is usually rather moderate, most often ranging from 30 to 60 degrees. Considered as a whole, the prevailing strike of the foliation ranges from north and south to northwest and southeast with dips almost uniformly toward the east. The northern central portion is exceptional with its east and west strike and northward dip. Also there are important departures from the prevailing direction of dip and strike in cer- tain Grenville areas as south of Johnsburg, south of Thurman, and between Pottersville and Starbuckville, in which areas the direc- tions are very variable. On the Long lake sheet, according to Professor Cushing, the foliation is more erratic in the eruptives ‘than in the Grenville, but here precisely the reverse is true. FOLDING Before any important general statements can be made regard- ing the character of the folding, a wider area will have to be studied. A striking feature is the almost uniform eastward to northeastward dip of the foliation, which suggests the possibility of isoclinal folding but aside from this uniform direction of dip, there is much evidence against such isoclinal folding. The gen- erally moderate angles of dip; the perfect agreement of foliation and bedding planes even where the strikes and dips are erratic; and the utter lack of any evidence for repetition of the strata even in long sections like that of figure 1 are strong points against isoclinal folding. Professors Cushing and Kemp recently stated 60 . NEW YORK. STATE MUSEUM with reference to the Long Lake and Port Henry-Elizabethtown quadrangles that the Precambric rocks show no good evidence of having been more than moderately folded or tilted, and this ap- pears to be true of the North Creek quadrangle as well. Locally, the limestone and accompanying pyroxene gneiss may be — intensely contorted or twisted, probably being due to the more ~ plastic character of the limestone when subjected to great pres- sure. The pyroxenic bands are often pulled apart into small lens- like masses as shown in plate 11 and figure 9. Other fine cases of contorted limestone may be seen at the river bridge near Thur- — man station (off the map); just north of the Ferry at the river's edge (see plate 3); along the road 114 miles southwest of Kelm —_— pond; and along the road a little east of north of County House mountain. ; : Ff Figure 9 represents a sketch, drawn to scale, of a mass of lime- &§ stone on the south side of Crane mountain which has been con- ~~ torted and forced for 20 feet across the foliation bands of the associated hornblende-garnet gneiss. | ‘ Fig. 9 Sketch showing a peculiar arrangement of Grenville rocks a seen by the roadside on the south side of Crane mountain and three-fifths — of a mile from the summit of the mountain. The limestone has been con-— torted and forced across the foliation bands of the associated gneiss. The black patches represent drawnout fragments of pyroxenic gneiss. “ SURFACE OF THE GREAT SYENITE-GRANITE INTRUSIVE Mage a The very ancient Grenville strata were invaded by a vast mass” of molten syenite and granite which, in part, pushed aside or up- ward or engulfed some of the Grenville and, in part, left patches of greater or lesser extent practically intact. This has largely given rise to the very decided “ patchwork” appearance of the geologic | map. 4 | 4 ) / a 1 & ie “Wi . - 7 rs i ae i Plate 12 W. J. Miller, photo Contorted Grenville limestone as seen near the road one and one-half miles southeast of Johnsburg. The darker streaks are pyroxenic bands which have been badly twisted and drawn out. GEOLOGY OF THE NORTH CREEK QUADRANGLE 61 The sharpness of the contact between the igneous rocks and the Grenville and the altitude of the igneous masses above the Gren- ville have often been accentuated by the faulting, but in spite of this some idea of the irregular surface of the great intrusive mass may be gained. Thus, the Grenville between Kelm and County House mountains occupies a depression fully 300 or 400 feet deep in the granite porphyry; while between Mill and Oven mountains the Grenville occupies a depression some 700 or 800 feet deep in the granite. Even if we grant the possibility of some faulting of the Pine-Gage mountain mass, it seems clear that this igneous rock rose by intrusion some hundreds of feet through the Grenville. In spite of the accentuated heights of the igneous masses of Hack- ensack, Moon, Heath, Potter, Huckleberry, and Crane mountains, -it seems necessary to regard a considerable amount of the eleva- tion of the igneous rocks above the Grenville as due to the intru- sion itself. The only other alternative is the untenable view that faults completely surround these igneous bodies. In general, then, we see that the great intrusive body often shows irregularities on its surface which vary in altitude by hun- dreds of feet within from I to 3 or 4 miles. TOPOGRAPHY RELATION OF TOPOGRAPHY TO ROCK CHARACTER The surface configuration of the North Creek sheet is almost perfectly adjusted to rock character. A glance at the geologic map will show that the Grenville rocks, with few exceptions, occupy the lowlands; this is because of the relative weakness of those rocks as compared with the intrusives. The limestone areas or belts, being weakest of all, are invariably found in the valleys, and stream courses have commonly developed along such _ belts. Occasionally the more resistant Grenville gneisses, even where un- affected by faulting, have stood out fairly well against erosion as, for example, south of Valentine pond and south-southwest of Thurman. The Grenville quartzite being quite pure and very resistant usually stands out fairly conspicuously in the Grenville areas. This is well shown in the area south of Warner pond, though the height is there accentuated by faulting. The steep slope of the quartzite ridge east of Tripp pond appears to be due to more rapid wearing away of the much weaker underlying Gren- ville. In the mixed gneiss areas, particularly where the Grenville is abundant, the topographic development has been very similar to that of the Grenville areas. 62 . NEW YORK STATE MUSEUM The igneous rocks, where homogeneous and free from Grenville — inclusions, without exception form the highest mountain masses. — Occasionally the gabbro bosses appear to be slightly more resistant ~ than the country rock and they then form the tops of low mountains — or hills. . Another topographic feature often locally conspicuous is the qi sand flat or flat-topped sand terrace. Among the best examples are: in the vicinity of Warrensburg and Pottersville, west of Star- — buckville, southwest of North Creek, and at a number of places southwest of Johnsburg. These represent delta deposits which © were formed in glacial lakes which will be described in the suc- — ceeding pages. RELATION OF TOPOGRAPHY TO ROCK STRUCTURES Some of the most prominent topographic features of the quad- ~ rangle are the bold escarpments, more or less well-defined ridges, — and isolated mountain masses or domes of igneous rock. These rock domes will be especially treated under the next heading. a Most of the escarpments or ridges are due to faulting and have already been described. Some ridges, however, especially those in © the Grenville areas, are due to other structural features combined — with rock character. Thus the prominent ridge of gneiss which ~ runs several miles southeastward from North Creek is due to the — fact that a belt of weak limestone everywhere dips sharply under the harder rock of the ridge. The ridge south of Valentine pond is to be explained in a similar manner. Many small streams in the Grenville have developed along structural belts of weakness. In the igneous rocks, too, there is a notable tendency for local : short ridges and valleys to develop along lines parallel to the direc- tion of foliation. The most remarkable topographic feature in the whole region is the deep, narrow rift between Crane and Huckleberry moun- tains, which is certainly due to a combination of faulting, a belt of weak Grenville, and some erosion since the faulting. EXFOLIATION DOMES ! gy One of the most striking features of the landscape, especially - in the southern two-thirds of the quadrangle, is the prevalence of distinct, isolated, domelike, topographic forms which rise hundreds 1 For a fuller discussion of this subject, see paper by the writer in N. vq State Mus. Bul. 149, p. 187~04. . Plate 13 W. J. Miller, photo Mill mountain, as seen from a point three-fourths of a mile to the south- west. This is a perfectly isolated dome of gray to pinkish-gray granite which rises fully 700 feet above the surrounding country. 7 ’ 4 . ar . j \ \ 7 4 ; ‘ is sd t - ‘ * , ~ r - . ® a * > Vy ¢ Pan TT? > t LJ ‘AO][VA IY} DAOGV od} OOZ SaSII DWOP IY] ‘ajsuvipenb ay} UIYYM UOWLWWOS OS BIB YOIYM SoWOP UOT}eI[OJXd OY} JO o[dwexso ouy e& SI Ureyunow siyy, “punoisoiof dy} Ul AQ][VA OY} SI[1apUN DUOJSOWI] O][IAUBIF) OTM ‘sseu urTeyUNOW oy} dn soayeUW d}1UaAs-zZ}1eN~) "}saMmyNos “YynNos ojlut suo yurod & WOIF PaMdIA SB ‘YSinqsudtVAA JO JSoOMY}IOU-jSOM SoTIW InNOF ‘ureyunoU 19}j0g ojoyd “AoTTTA “£ “AA VI a3e[d GEOLOGY OF THE NORTH CREEK QUADRANGLE 63 of feet above the comparatively lowland of the region. A com- parison of the North Creek sheet with all other published Adiron- dack maps shows that, from the physiographic standpoint, this region is noticeably different from the Adirondacks in general. Some of the best examples of such domes are: Kelm, Chase, Tripp, Hackensack, Moon, Heath, Potter, Birch, No. 9, Little, Crane, Huckleberry, Mill, Stockton, and Prospect mountains. The greatest of these domes is Crane mountain which rises 2000 feet above the immediately surrounding country. The upper 1000 to 1500 feet of this mountain are very steep to almost precipitous on all sides except the north making this great rock dome a grand sight as viewed from Thurman (see plate 8). Mill and Stock- ton mountains deserve special mention because they rise as two great isolated masses above the comparatively low and featureless surrounding country and form conspicuous features of the land- scape as viewed from any of the higher points for a number of miles around (see plate 13). As viewed from the south, Potter mountain is a fine example of a rock dome which rises 700 feet above the general level of the country (see plate 14). The domes may be classified under three headings according to shape: (1) those with nearly circular bases and which are very symmetrical and almost uniformly steep on all sides, as Potash, Mill, and Stockton mountains and the top of Kelm mountain; (2) those with elliptical bases and represented by nearly concentric elliptical contours to the summit, as Moon, Birch, No. 9, and Huckleberry mountains; and (3) those of irregular shape as shown on a large scale by Crane mountain and many smaller masses. After climbing all the domes the writer has been impressed by the almost universal occurrence of exfoliation on a large scale over their surfaces. These mountains are literally peeling or shelling off by the removal of exfoliation sheets of great size, some having been noted as much as 50 to 75 feet across and from 1 to 3 feet thick. Among many other good places to observe this phenomenon are on the west or south sides of Moon, Crane, or Huckleberry mountains. Not infrequently, especially during the fall and spring months, slabs loosen up and go thundering down the mountain sides. Though the rocks are all clearly gneissoid, the ‘exfoliation appears entirely to disregard this structure and often great sheets come off at right angles to the foliation. This very common occurrence of exfoliation domes in the region the writer believes to be due to a combination of factors especially 64 NEW YORK STATE MUSEUM » prominent in this part of the Adirondacks. Among these factors are: (1) character and distribution of the rocks whereby small to large masses of hard, homogeneous, igneous rocks have broken through the comparatively weak Grenville strata to produce a sort of “ patchwork” effect so that, as a result of long erosion, the hard, igneous masses have stood out prominently above the Grenville; (2) faulting, whereby the “patchwork” effect and steep scarps have been either produced or sharply accentuated; (3) glaciation, whereby the isolated mountains of igneous rock were swept clean of decomposed surface rock and more or less smoothed or rounded off, thus favoring postglacial exfoliation; and (4) temperature changes, humidity etc., whereby the bare slopes of the isolated elevations of crystalline rock, under the conditions of comparatively rapid temperature changes in this the driest part of the State, are favorable for exfoliation. PENEPLAINS It is well known, especially as a result of the work .of Professor Kemp and, more recently, that of Professor Cushing on the Sara- toga sheet and of the writer on the Broadalbin sheet, that the south- eastern Adirondack region had been worn down to the condition of a fairly good peneplain immediately prior to the advance of the upper Cambric (Potsdam) sea. Altitudes above the general pene- plain level were not over a few hundred feet at the most. This conclusion has been reached through a study of those places along the borders of the Adirondacks where the Paleozoic rocks directly overlie the Precambrics. The position of the North Creek quad- rangle renders it practically certain that this very ancient (Cam- bric) peneplain extended over its area, but because of the exten- sive faulting and erosion of the region, that old peneplain surface ° is nowhere certainly recognizable. Again, it is well known that, by the close of the Mesozoic era, a fairly well-developed peneplain condition had once more been ~ produced over this region in common with southern New England, New York, and the northern Appalachians. Professor Davis has shown ! that the Berkshire hills area, during the late Mesozoic, had been worn down to a fairly good peneplain with occasional low mountains (monadnocks) rising above the general level. There is strong reason to believe that a similar condition prevailed over the southeastern Adirondack region, but with the monadnock 1 Physical Geography of Southern New England in Physiography of the United States. GEOLOGY OF THE NORTH CREEK QUADRANGLE 65 feature probably even more prominent. The comparatively even sky line of the western Adirondacks together with the high plateau called Tug Hill just west of the Black River valley, practically prove the former peneplain condition of that portion of the Adirondacks. This peneplain is known to have been elevated late in the Cretacic period or the early Tertiary period and, as already stated, much of the faulting of the eastern Adirondacks occurred at the time of that great uplift or even later. Thus the fact that this peneplain had considerable irregularities on its surface, com- bined with the facts of excessive tilting of the earth blocks by fault- ing and subsequent erosion, have quite effectually masked even this later peneplain surface. Doctor Ogilvie says with reference to the Paradox lake quadrangle,’ that the even sky line of some of the mountains suggests an uplifted peneplain, and also that the long, smooth, eastward slopes of the fault blocks probably represent por- tions of the peneplain surface which were produced before the faulting. Similar evidences occur within the North Creek quad- rangle as, for example, the rather even sky lines of the Henderson, Pine-Gage, Huckleberry, and Chase mountain masses, and the numerous eastward-sloping fault blocks already described. Any- thing like accurate knowledge of the character of this Mesozoic peneplain within the map limits is, however, lacking. GLACIAL AND POSTGLACIAL GEOLOGY CHANGES OF LEVEL It is important to recall the well-known fact that the eastern portion of North America, including the Adirondack region, 1m- mediately preceding and doubtless during a good part of the Glacial epoch was notably higher than it is today. The submerged chan- nels of the lower Hudson and St Lawrence rivers prove that the land there must have been something more than 1000 feet higher than now in order to have allowed the channel cutting. Toward the closing stages of the Ice age, and directly after it, there was a submergence of the whole region to below the present level as shown by the so-called raised beaches or delta deposits in the Hud- son and Champlain valleys. In the Champlain valley the deposits are chiefly clays which were formed in an arm of the sea as proved by the presence of marine fossils. These deposits are now several hundred feet above sea level in the Champlain valley, which proves 1N. Y. State Mus. Bul. 96, p. 468. 66 NEW YORK STATE MUSEUM at once that during the time of maximum subsidence the region stood several hundred feet lower than now, and that the most recent land movement has been one of elevation which has brought the marine deposits to their present position several hundred feet above sea level. This last (upward) movement has a direct bear- ing upon the glacial lake deposits of the North Creek quadrangle, and it is important to note that this upward movement was dif- ferential with greatest uplift toward the north. Using the figures of Professor Woodworth, the greater uplift of the land toward the north, passing along the southern part of the Champlain val- ley, has amounted to about 3% feet a mile." Practically this same figure may. be applied to the North Creek area since it is so close to the southern end of the Champlain valley. DIRECTION OF ICE FLOW The evidence is conclusive that the North Creek quadrangle was vigorously glaciated. Many widely distributed glacial striae — sixty in all—have been observed within the map limits and are all recorded on the geologic map.. Such a large number of striae is very unusual, certainly being far greater than for any other quadrangle so far mapped in the eastern, central, or southern Ad- irondacks. As usual the striae are most frequently seen along the highways in the valleys and on ledges from which the glacial drift covering has recently been removed. A number of striae have been found away from the roads and even on mountain sides, but never on mountain tops because where exposed on the bare ledges they have been obliterated by postglacial weathering. Of the sixty recorded striae, the extreme range in direction 1s only from south 20° east to south 20° west, with the north-south direction nearly an average. In fact many of the striae do run north-south and very few vary more than 10° either side of this. The direction of ice movement indicated by these striae is excep- tional for the central and eastern Adirondacks as judged by obser-_ vations made on the Long lake, Paradox lake, and Elizabethtown- Port Henry sheets over which areas the general movement was —_ ae . A ye southwestward at the time of maximum glaciation. The reason — for the southward movement over the North Creek sheet is not an easy thing to account for, though it may possibly have been due to a crowding of the ice into the Hudson valley and a local deflec- tion of the general southwesterly current where the ice flowed 1N. Y. State Mus. Bul. 84, p. 206, 228 and plate 28. 4 | EIB tap GA te EIA OEIC DS BGR GEOLOGY OF THE NORTH CREEK QUADRANGLE 67 against the much higher mountains which are arranged along the eastern side of the adjoining Thirteenth Lake sheet. Some of the striae are so situated in valleys as to suggest that, locally at least, the ice currents followed the valleys, but many others are situated wholly without reference to the topography. Among the best examples of striae which are significant as proving that the general ice movement was irrespective of even the major topographic features are the following: just north of Mud pond and immediately south of the Huckleberry-Crane-Little mountain masses, thus showing the retention of the southward course in spite of those mountains; immediately under the steep fault scarp on the east side of Loon lake; at the north bases of Pine and Gage mountains, showing that the ice current headed straight for those high mountains; and on the hilltop just northwest of Johnsburg where the ice left its record after having plowed diagonally up the hill for an altitude of several hundred feet instead of following the valley. The great depth of ice over the region is proved by the frequent occurrence of drift boulders even on the high mountains, the high altitudes of some of the striae, and the glacial lake on Crane moun- tain. Some of the striae at considerable altitudes are as follows: north of Mud pond (southwest corner) at nearly 2000 feet; 2 miles east of Cherry ridge at from 1500 to 1600 feet; west base of No. 9 mountain at 1600 feet; 214 miles southwest of Johnsburg; at 1550 feet; on the side of Stockton mountain at over 1500 feet; and one-half of a mile northwest of Johnsburg on a hilltop at 1480 feet. On this basis, granting a fairly level ice surface, the depth of ice must have been at least 1000 feet or the difference between these highest striae and the Hudson river to the east. However, the presence of the glacial lake with drift dam well up on Crane mountain, and at an altitude of 2620 feet, shows that the ice was deep enough to cover the mountain that high up at least. Accord- ing to this the ice must have been at least 1500 feet deep in the valley just north of Thurman and fully 2000 feet deep in the valley of the Hudson river. ICE EROSION To say the least, ice erosion was very effective in the removal of nearly all preglacial soils, decomposed rock, and loose joint blocks. The mountains were swept clean of such materials and left standing as more or less rounded off bare rock ledges, while during 3 EE GS NEW YORK STATE MUSEUM = the retreat of the great ice sheet the valleys were partially filled with drift deposits. Decomposed rock material of preglacial age vd rep ann io , . i od , é cos . ~ 7 - eas s a ON et ee ‘ Be: i "4 oy ae oe aes . ons { ste Tes, : eh age amy a AM r Ne i ev REAR oy oo) “9 Fe “Gd P ere pc Pio bre At We nae me iM EDUCATION DEPARTMENT NIVERSITY TATE OF NEW YORK JOHN M. CLARKE MUSEUM ¥ Noeza _ BULLETIN 170 N c STATE GEOLOGIST REEK QUADRANGLE IGNEOUS ROCKS LATE SERIES a Diabase dikes Gra | | BB | SCN ieanans Nis tercat S| s Zz GF t { ~ S . ; $ Gabbro stocks and dikes The most typical rock ts a horn- blende or Aypersihene gabbro, but there ts much variation among the stocks even to some of diorific or syenitic make-up. The more basic alocks are seldom guaizsoid, while {he acidic masses are aften gneiss oid. EARLY SERIEg Granite A distinctly gneissoid, greenish to pinkish-gray, very’ quarlsore phase of the syenile, and (nter mediale between the’ syenite and granite porphyry. MIXED SERIES SEDIMENTARY ROCKS Gen MME Me Cipygly ROSSI Lie Les SEs Grenyilie gneisses, inclu cing all Precambric sediments not be- low mentioned These rocks are usally clearly banded. Grenville crystalline limestone interbedded with hornblende and hornblende-garnet gneisses Timestone usually graphitic, (Thirteenth Lake) GRENVILLE SERIES Wy uartzite ly bedded, pure 101%; inches fied etth thi layers of biotite gnetss, SS x Dip and strike of foliation Glacial striae ® Mines and quarries x Limestone outcrops AA, BB, CG, DD and EE the Ines of stracture tions shown in figu: 5, 6, 7 wud 8 respectively (Luxerne) Geology by W. J. Miller, 1 : @ FO Nae ae z Stites 4810-1911 2 Bie ate ae ss cere t Re ee a See + pXlometers Contour interval. 20 feet Dessarrn te meen sees teved PRECAMBRIC ROCKS a 7 , * roiks a 7 c a ll < ae -. y BG gO TR om ~ ee q % vj - J“ a ee eta ee tit tiene eter cas iacsanenncl CA sApAR™ AANA WAAR on ~~ am 7 a ~ Pana! Agintal alt alade f. A {yr pone’ Sree. ‘ AAR, prrncPnrnnsnanrn nage eA hr pae PAAR, V Ann ABA a) Wal TT Pi ph Apap” pr WPA LLL A. A ANAMAAS Aa, fp rp nasa™ Cone ma ahyae 8! 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