40 Expedition to the 



basin of the Mississippi and its tributaries. This formation, 

 like others of the same period, is rough, with small elevations, 

 which are most considerable on its borders, and diminish in 

 proportion, as we approach nearer its central parts. 



Compact limestone, and sandstone of several varieties, 

 are the rocks which invariably occur along that portion of the 

 Ohio we are now consideriag. Sandstone of a light gray 

 or ashen colour, of a compact texture, an argillaceous cement, 

 and a slaty or lamellated structure, is the most abundant, and 

 occupies the lowest points which we have hitherto been able 

 to examine. This rock frequently contains alternating beds 

 of coal, bituminous shale, and its accompanying minerals. The 

 beds of compact limestone, which occur in this region, usual- 

 ly rest upon the sandstone just mentioned. Considered as a 

 stratum, its distribution is the reverse of that of the sand- 

 stone. It occupies the central and least elevated portions of 

 the formation, and on the borders where the sandstone is 

 most abundant, the limestone is of less extent and of more 

 uncommon occurrence. These remarks are applicable to the 

 hilly district on the upper portion of the Ohio river. From 

 Pittsburgh to Cincinnati, the prospect from the river is that 

 of hills of moderate elevation, sometimes rocky and abrupt, 

 but often sufficiently gradual in their ascent, to admit of cul- 

 tivation to their summits. Their character, as to extent, di- 

 rection, &c. seems to be determined by the number, direc- 

 tion and magnitude of the streams which traverse them. 

 They are the remains of what was formerly a continuous 

 and nearly horizontal stratum, with a large deposit of super- 

 incumbent soil, which the flowing of water, during the lapse 

 of ages, has channelled and excavated to its present form. 

 These hills diminish in altitude as you approach the falls 

 from above ; there they again rise to a height nearly equal to 

 what they attain at the head of the river, and from thence 

 gradually diminish, until they disappear, a little above the 

 confluence of the Ohio and Green rivers. Here commences 



