GEOLOGY. 237 



tion of the rest (with the single exception of the blue lime- 

 stone, upon which, also, it much encroaches) is peculiar, so 

 far as my observations in the Western States extend, to the 

 district of country which is the object of the present report. 

 In the north of this district, the cliff limestone appears to run 

 out, the blue limestone and underlying sandstones coming to 

 the surface. South, it disappears beneath the coal-measures. 

 East, it seems to be chiefly covered up by recent deposits, 

 extending, probably, in an east or southeasterly direction 

 beneath these, across the States of Illinois and Indiana, into 

 the State of Ohio. And west, so far as our examinations 

 went, it is also chiefly covered up by recent deposits, occur- 

 ring, however, occasionally, in the beds of the streams, and 

 projecting, at first in clifls, and at last only in low ledges, 

 from their banks. 



" The general geological character of the country explored 

 may, then, be thus briefly summed up. It belongs to that 

 class of rocks called, by recent geologists, secondary, and, by 

 others, occasionally included in the transition series. It 

 belongs, further, to a division of this class of rocks, described, 

 in Europe, as the mountain limestone, or, sometimes, as the 

 carboniferous, or metalliferous, or encrinital limestone. And 

 it belongs, yet more especially, to a subdivision of this group, 

 known popularly, where it occurs in the west, as the clifl" 

 limestone, and described under that name by the geologists 

 of Ohio. 



" This last is the rock formation in which the lead, copper, 

 iron, and zinc, of the region under consideration, are almost 

 exclusively found ; and its unusual development, doubtless, 

 much conduces to the extraordinary mineral riches of this 

 favored region. It, therefore, demands, and shall hereafter 

 receive, particular analysis and attention. 



" In the northern portion of the district surveyed, an 



