246 J. J. Stevenson—Surface Geology of Pennsylvania. 
The Horizontal Benches. 
Benches belonging to this series have been fully recognized 
over the whole area examined. The altitudes are as follows :— 
Above tide. Above tide. Above tide. 
1, 2,580 feet. 8. 1,570 feet. 15. 1,290 feet. 
2, 2,40 S 1520 > 16. 1,270 .* 
Bi 2308... ©. 10, 1.475 . * 17, 3,240. © 
4, 2.288 “ tt, ooo. * 18, ‘t,100 2* 
5; 3.083" * 13, ¥420 ° = 18. 1160 
6. 1,820 “ 12, Tee0 | * 20. 1,100 “ 
i. 1,600 = 14, 1,850 “ 
Of these benches, those below No. 11 were recognized at 
many localities within an area of more than 5,000 square miles ; 
extreme variation in level is barely twenty feet in any case and 
in most of the benches the altitude is accurately the same at all 
places. No. 17 shows a variation of eighteen feet, and I am 
much inclined to believe that I have confounded two benches 
a long distance north and south and is broken only by gaps 
which the pales streams make through this small ridge on 
i the Monongahela River. He sees also that this 
plain is the divide between two valleys, one at the east between 
this and Chestnut Ridge, and the other at the west, in which 
an plain of Brush Ridge, as well as by lower benches which 
veak its continuity and convert it into'a succession of basins. 
