480 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



The Shawangunk formation of the Front Eidge of the northern Ap- 

 palachians. — Considering now more fully the distribution and character, 

 of the typical Shawangunk conglomerate, we begin with the fact that its 

 greatest known thickness is in the Kittatinny Mountains in the region of 

 the Delaware Water Gap, where, as already noted, it aggregates 1,900 

 feet. The formation rest unconformably on the Hudson beds, beginning 

 with a coarse pebble conglomerate, in which, besides the prevalent quartz 

 pebbles, pebbles of compact mud rock are also found. This same general 

 relationship to the Hudson beds is maintained in all the sections north- 

 ward to near Kingston, New York, and southward for some distance be- 

 yond the Schuylkill Eiver. Northward the thickness decreases, accord- 

 ing to the measurements of Billingsley, to 1,500 feet at Culvers Gap, 

 New Jersey, 800 feet at Otisville, New York, and to 500 feet at Minne- 

 waska, New York. At High Falls the thickness, according to the borings 

 made by the Metropolitan Water Board, is 3l5 feet, while at Eosendale 

 scarcely 100 feet persist. Finally, at Binnewater station, there remain 

 only 10 feet of conglomerate, and near Kingston it has disappeared alto- 

 gether. The distance from its thickest point at the Delaware Water Gap 

 to the point where it disappears north of Binnewater is almost exactly 

 100 miles, giving an average decline of 19 feet per mile. Southwestward 

 the decrease in the thickness is to 1,500 feet at the Wind Gap, 1,125 feet 

 at the Lehigh Water Gap, and 590 feet at the Schuylkill Water Gap, 

 The distance to this point is only about 55 miles, giving an average de- 

 crease of 24 feet per mile. That the formation has not entirely disap- 

 peared after it ceases to be a prominent feature in the landscape is shown 

 by the occurrence of a sandstone of the same age, and apparently consti- 

 tuting its southward extension on the Maryland border, nearly 175 miles 

 southwest from the Delaware Water Gap. This will be referred to again 

 later on. No trace of the rock is known in the northwestern outcrops of 

 the Paleozoic strata, and it is not unlikely that its actual extent under 

 cover is not much north or west of Elmira, New York. The Ithaca deep 

 well did not reach the bottom of the Salina formation, and the one at 

 Seneca Falls, Seneca County, New York, which passes through this for- 

 mation, shows no recognizable representative of the Shawangunk, the red 

 Vernon shales, with some mottled red and green shale, totaling 250 feet, 

 lying directly on the Niagaran limestone series. 81 In general character 

 the Shawangunk is a white quartz pebble conglomerate, but with many 

 intercalated layers of sandstone and shale. The change from the one to 

 the other is generally abrupt. Very often the sandy layers show the com- 



81 C. S. Frosser : American Geologist, vol. vi, 1890, p. 203. 



