66 J. J. STEVENSON CARBONIFEROUS OF APPALACHIAN BASIN 



of the coal beds are irregular, but are fairly persistent, having been ob- 

 served at many places.* 



Crawford county is west from Warren and extends to the Ohio line. 

 The Pottsville remains only in the southern part, where Doctor White 

 obtained the section, so often referred to in the foregoing pages. It is 



Feet 



Home wood sandstone 50 



Mercer group 30 



Connoquenessing group 120 



Sharon shales 50 



Sharon conglomerate 45 



with an extreme thickness of 300 feet. As in Forest, the Connoquenes- 

 sing is double ; the sandstones are each 35 feet, a little thinner than in 

 Forest, but the intervening shale in crossing Venango county has thick- 

 ened to 50 feet. The upper sandstone, white to grayish white, is more 

 or less pebbly. The intervening shales, the Quakertown of White, show 

 coal at only one locality. The lower sandstone is hard, coarse, and 

 brown, often micaceous and sometimes pebbty. It is less persistent 

 than the upper, being divided at times by 20 to 30 feet of shale. 



The Sharon shales are from 25 to 50 feet thick, the variation being 

 due to that in the Lower Connoquenessing sandstone. Where thick, 

 they show a coal bed in the upper part ; the Sharon bed, below the 

 middle, is thin and poor, appearing only occasionally along the outcrop 

 and rarely becoming thick enough to be worked. 



The Sharon sandstone retains the character so frequently observed in 

 the counties already crossed, in that the upper part is sandstone, while 

 the lower part is a coarse conglomerate for about 10 feet. The pebbles 

 are not so large in Crawford as at more eastern localities, being seldom 

 larger than a hen's egg, whereas at Tidioute, in Warren, they are some- 

 times as large as a goose's egg. Everywhere the pebbles are ovoid, though 

 Ashburner speaks of them in Forest county as occasionally rather angu- 

 lar. The thickness has diminished from 100 to less than 50 feet in 

 crossing Venango county. The northern line of outcrop is from the Ohio 

 line in southwest Crawford to northeast Warren.f 



In Mercer county south from Crawford the Homewood sandstone is 

 from 30 to 70 feet, being thickest at the north and varying from good 

 building stone to coarse conglomerate. New members appear in the 

 Mercer group, which here contains two coal beds and two limestones. 

 The upper limestone is less persistent than the lower, which is present 



* C. A. Ashburner,: Report of Progress in Forest County (RR), 1885, pp. 307-316. 

 1 1. C White : Geology of Crawford and Erie Counties (Q 4), 1881, pp. 55, 56. 





