542 C. SCHUCHERT SILURIAN FORMATIONS 



Near Binnewater the Binnewater sandstone rests abruptly on the High 

 Fall shales, indicating, it is thought, a hiatus here in sedimentation. 

 Here the upper part of the High Falls shales consists of green, blue, 

 and black limy and somewhat sandy shales (12 feet), followed below 

 by brick-red sandy shales (25 feet) that are much sun-cracked; the 

 latter rest on 10 feet of Shawangunk conglomerate. 



Great break. All of Niagaran series absent. 



Silurian. 



Shawangunk conglomerate. North of Binnewater 10 feet of Shawangunk 

 is exposed in the midst of the High Falls shale. Just what the struc- 

 tural relation of one is to the other the writer could not determine. 

 The uppermost part of the Shawangunk is seen at the Rock Cliff House 

 in High Falls. Here about 30 feet is exposed beside the road, and con- 

 sists of a milky white conglomeratic quartzite with the small vein 

 quartz pebbles (up to 1 inch in diameter) well rounded and imbedded 

 in a clean sand. Arthrophycus alleghaniense was found here by Pro- 

 fessor Van Ingen. The remainder of the Shawangunk is exposed in 

 the gorge of the Rondout, and the contact with the High Falls shale 

 is shown near the power-house of the Electric Light and Power Com- 

 pany. 



Rondout Valley underground geology. — Five miles west of High Falls. 

 A number of drill holes (cores) were put down by the New York City 

 Board of Water Supply across the Kondout Valley, and the following- 

 description of the rocks is much condensed from Brown : American 

 Journal of Science (4), volume 37, 1914, pages 464-474. 



Devonian. Helderbergian series. 



Binnewater sandstone, 52 to 62 feet thick. At the top a thin layer of 

 hard, white, quartzitic sandstone, followed by alternating thin beds 

 of porous sandstone and green shale that are more or less calcareous 

 and full of small cavities. The transition downward is said by Brown 

 to be complete into the Silurian. 



Silurian. Cayugan series. 



High Falls shale. Thickness averaging between 90 and 100 feet. A 

 variable shale and pyritiferous formation. An upper shale member 

 that as a rule is green or gray in color (27 to 37 feet thick), a middle 

 dark to black sandy zone (12 to 15 feet), and a lower green to black 

 shale division (40 to 50 feet). At the surface this formation is pre- 

 dominantly red in color, but this appears to be due largely or wholly 

 to aerial oxidation. The cores show that the farther the formation is 

 away from the surface the more the strata lose their red color. The 

 transition to the underlying conglomerate is said to be a gradual one, 

 not an abrupt contact or unconformity. However, in shaft 7 Brown 

 distinctly notes a coarse conglomerate at the top of the Shawangunk 

 (6 to 8 feet) and in the basal 2 feet of the High Falls shale, all of 

 which can as well be interpreted as the invading base of the latter 



