548 C. SCIIUCHERT SILURIAN FORMATIONS 



of the river along the upper railway cutting. It should be added here 

 that the higher strata of this Upper Shawangunk may actually be of 

 early Clinton time, a correlation suggested by the physical nature of 

 the strata (as at Otisville) and by the presence of ButhotrepMs 

 gracilis Hall. 



Lower Shawangunk. Thin-bedded greenish and conglomeratic clean 

 quartzites, with very thin shale partings, 350 feet thick. Vein quartz 

 pebbles are all small, decreasing in size upward. Thick and thin 

 bedded, abundantly conglomeratic, cleanly washed quartzites, with or 

 without shale partings, as follows: (1) Tliin-bedded, greenish sand- 

 stones, with thin shale partings (157 feet) ; (2) Dark colored, thick 

 bedded, conglomeratic quartzite with small and large vein quartz 

 pebbles (40); (3) light colored, heavy-bedded quartzite with dark 

 zones but without conglomerate (65) ; (4) thick-bedded, dark quartz- 

 ite with an abundance of thin and thick conglomerate zones with the 

 vein quartz pebbles large, and among them many of black flint 

 (?Cambrian age), some of black shale and very rarely one of serpen- 

 tine (80). The basal 8 feet are made up of (1) rotten quartzite with 

 large, well rounded quartzite pebbles, probably of Cambrian age, and 

 more rarely vein quartz pebbles (6) ; (2) a pebble bed as before with 

 the stones ranging up to 6 inches across (18 inches), and (3) rotten 

 sandy shales (6 inches). The contact with the Hudson River is dis- 

 conformable. 



E. T. Wherry (Science, September 24, 1909, page 416) reports "two 

 small areas of Shawangunk conglomerate, preserved by down-faulting 

 some 20 miles south of the main exposure in the Blue Ridge [of the 

 Lehigh Gap], corresponding in position and lithologic character to the 

 Green Pond of New Jersey." 



Ordovician. 



Great break. All of Richmondian absent. 



Hudson River formation. Greenish sandy shales with zones of thin-bedded 

 sandstones. At 25 feet and 75 feet beneath the Shawangunk occur 

 sparingly Diplograptus foliaceus var. vespertinus Ruedemann. 



Schuylkill Gap at Port Clinton, Pennsylvania. — Twenty-six miles 

 southwest of Lehigh Gap. See Second Geological Survey of Pennsyl- 

 vania, Final Beport, volume I, 1892, pages 632, 643, 673; volume IT, 

 1892, page 733; also Eeport G6 of the same series. The geology in this 

 gap of the Little Schuylkill Eiver is much complicated by folding, and 

 especially by faulting; so that the detail is not easily made out. 



Silurian. Cayugan series. The Second Pennsylvania Survey gives the thick- 

 ness of these red beds as about 3,000 feet. 



Great break. All Nlagaran absent. 



Silurian. 



Shawangunk formation. The Second Pennsylvania Survey gives the sec- 

 tion as follows : 



