THE SILURIAN SECTIONS 545 



tion. All of the sandstones have grains and small nodules of siderite 

 that on weathering give them a more or less spotted appearance. This 

 feature is most marked at Otisville, but is also seen elsewhere. 



The basal 7 feet of the Shawangunk is a conglomerate, with the quartz 

 pebbles ranging between .75 and 1.25 inches; there is also an occa- 

 sional one of the Hudson River sandstones. The contact with the 



_ Hudson River is unconformable. 



Shawangunk Mountain continues from Otisville northeast for 45 miles 



and ends abruptly at Rosendale. At Otisville the thickness of the 



Shawangunk is 800 feet, and 24 miles to the northeast, at Minnewaska, 



it is reduced to 500 feet (Grabau). Farther north Mather states that 



: it thins to 150 and finally to 00 feet. 



Arthrophycus alleghaniense occurs in greatest abundance at 420 feet 

 above the Hudson River shales (see plate 20, figure 2). At this level 

 there are a number of black shales and these have the eurypterids de- 

 scribed by Clarke and Ruedemann (Eurypterus maria, Eusarcus (?) 

 eicerops, Dolichopterus otisius, D. stylonuroides, Stylonurus (Gtenop- 

 terus) cestrotus, S. myops, Hughmilleria shawangunk, and Pterygotus 

 (Erettopierus) gloMceps). Another zone of burrows occurs at 650 

 feet above the base of the Shawangunk and a third at 750 feet. It is 

 probable that others were seen at about 100 feet above the base. 



Ordovician. 



Great break. All of Richmondian absent. 



Hudson River series. For contact with Shawangunk see plate 21, figure 1. 

 Has small Climacograptus bicomis in abundance. A series of dark 

 green laminated shales with, rarely, a zone of graptolites. The dip is 

 41° northwest, strike north 41° east, while the superposed Shawan- 

 gunk has dip 34° northwest, strike 41° east, magnetic. From this we 

 learn that the Taconic foldings so pronounced at Kingston have nearly 

 died out in the 45 miles between these two places. 



Delaware Gap, New Jersey-Pennsylvania. — Fifty miles southwest of 

 Otisville. The following observations are made from the exposures on 

 both sides of the Delaware Eiver through Kittatinny Mountain. See 

 Rogers: Geology of Pennsylvania, volume I, 1858, pages 126-130, 271, 

 •277, plate at end of volume; Cook: Geology of New Jersey, 1868, page 

 1 46 ; Lesley : Second Geological Survey of Pennsylvania, Final Report, 

 volume I, 1892, pages 634, 638, 641, 675 ; also Report G6 of the same 

 series. 



Silurian. Cayugan series. This is the Clinton series of the Second Geological 

 Survey of Pennsylvania Reports and is given as 2,425 feet in thick 

 ness; Grabau (Bulletin of the Geological Society of America, volume 

 24, 1913, page 478) gives it as over 2.300 feet. The series is not fully 

 exposed, but appears to be made up of red shales and argillaceous 

 red .sandstones in beds from 2 to 20 feet thick, interbedded with many 

 beds of green, coarse. 'and much cross-bedded quartzites varying be- 

 tween 2 and 6 feet in thickness. The latter appear to be river ma- 



