THE SILURIAN SECTIONS 547 



Hudson River series consists of blue-black shales with about one-half 

 of the formation made up of thin and thick interbedded dark quartz- 

 ites. No fossils were seen. 



Lehigh Gap, Pennsylvania. — Twenty-eight miles southwest of Delaware 

 Gap. See Rogers: Geology of Pennsylvania, volume I, 1858, page 273, 

 and plate at end of volume ; Lesley : Second Geological Survey of Penn- 

 sylvania, Final Report, volume I, 1892, pages 641, 674; volume II, 1892, 

 page 731; also Report G6 of the same series. 



Silurian. Oayugan series. This series is seen to best advantage on the north 

 side of the river, in the vicinity of Lehigh Gap station of the New 

 Jersey Central Railroad. H. D. Rogers gives the thickness as about 

 1,630 feet; the Second Pennsylvania Survey as 1,275 feet, and adds 

 that it may be as thick as 3,275 feet. Grabau (op. cit., page 482) 

 gives the thickness as nearly 2,500 feet. The greater part of the series 

 consists of brick-red and greenish sandy micaceous shales and fine- 

 grained sandstones, somewhat rippled and sun-cracked. The lower 85 

 feet consist of thin and heavy bedded, greenish yellow sandstones with 

 thin shale partings ; the basal sandstone is 10 feet thick. The series 

 rests disconformably on the thinner bedded and more glossy Shawan- 

 gunk and may be seen along the wagon road and elsewhere in the 

 vicinity of the station. 



Great break. All of Niagaran absent. 



Silurian. 



Shawangunk formation. Can be studied to best advantage along the rail- 

 way cuttings and wagon road on the north side of the river between 

 the Ordovician exposures and tbe Chestnut Ridge Railroad. The 

 total thickness appears to be nearly 1,250 feet; Rogers (on plate at 

 end of volume) gives it as between 1.200 and 1,300, and the Second 

 Pennsylvania Survey as 1,125 feet. 



The Upper Shawangunk, 900 feet in thickness, is devoid of conglomerate 

 and consists of the following zones, going downward in the section : 

 (1) Light green shales (weathering to yellow, with silklike surfaces; 

 the same character pertains to most of the other green shale zones) 

 and sandy red shales, interbedded with three thick quartzites (70 

 feet) ; (2) greenish shales interbedded with thin beds of coarse green- 

 ish quartzites (150); (3) red shale zone (12). These three upper 

 zones may be equivalent to some part of the Clinton. (4) Thin-bedded 

 quartzites (8) ; (5) greenish shales (20) ; (6) curly shaly sandstones 

 (10) ; (7) greenish sandstones and shales with an occasional thin red 

 shale bed (40) ; (8) covered area (190) ; (9) thin and thick bedded 

 sandstones (25) ; (10) covered area (100) ; (11) thin-bedded sand- 

 stones and greenish shales with an occasional black shale (175) ; (12) 

 covered area (100). 



Near the bottom of this Upper Shawangunk series, or about 600 feet 

 above the Hudson River contact, Professor Barrell collected a speci- 

 men of Arthrophycus alleghaniense. It was found on the south side 



