GEOLOGY OF THE NEW YORK CITY AQUEDUCT 37 



(a) A lignitiferous sand with occasional clay beds farming the 

 uppermost of the Cretaceous series is probably equivalent to the 

 marl series of Xew Jersey. But it lacks the prominent greens and 

 development characteristic of the region further south. Not clearly 

 separable from the underlying formation or ]\Iatawan beds. 



(^j The 2^Iatawan beds. Gray sands and clays. 



(c) Raritan formation. Clays and sands, plastic clays, the Lloyd 

 sand, an important water carrier lies about 200 feet below the top 

 of the formation. Occasional leaf impressions. 



All of these formations, except where disturbed locally by glacial 

 ice, dip gently seaward. The sand beds of these strata are the chief 

 sources of underground water being developed by the new system. 



c Jura- Trias formations. (4) Palisade diabase. This is a thick 

 intrusive sheet, or sill, of igneous rock of diabasic type. It is 

 700-1000 feet thick. It lies for the most part parallel to the bed- 

 ding of the surrounding, inclosing, sedimentary rocks, and, rising 

 gently eastward, forms a strong cliff continuously along the west 

 bank of the Hudson for 40 miles. It varies from very fine to very 

 coarse texture and is for the most part fresh, tough, durable, and 

 is the source of large quantities of the most satisfactory quality of 

 crushed stone now on the market for use in concrete. 



(5) A'ezvark series. This is a very great thickness of silicious 

 sediments, chiefly reddish conglomerates, red and brown quartzose 

 and feldspathic sandstones and shales. They dip gently westward 

 and northwestward at 10-20 degrees, and are confined, in this 

 region, to the west side of the Hudson south of the Highlands. The 

 formation supphes " brownstone " for building purposes. 



None of the Jura-Trias rocks, so far as known, will be cut by the 

 aqueduct. 



d Devonic strata. (6) Catskill formation. This formationMs of 

 continental type, chiefly a conglomerate. A white conglomeratic 

 sandstone forming the uppermost portion attains its greatest thick- 

 ness on Slide mountain (350 feet). It is a '' coarse grained, heavy 

 bedded, moderately hard sandstone containing disseminated pebbles 

 of quartz or Hght colored quartzite, and streaks of conglomerate." 



A red conglomeratic sandstone constitutes the much thicker por- 

 tion below (1375 feet). It is a " coarse, heavy bedded sandstone of 

 dull brownish hue containing disseminated pebbles and conglom- 

 eratic streaks, dift'ering from the overlying beds chiefly in color. In 



1 Grabau, A. W. N. Y. State Mns. Bui. 92. Geology and Paleontology 

 of the Schoharie Valley. 



