J. Hail on Carboniferous Limestones of Mississippi Valley. 195 
the uplifting of the older rocks upon the north; and that this 
state of things continued throughout all the period of the lime- 
en 
inequality caused by this uplifting agency, and produced other 
wregularities of the surface. 
The coal measures extend much farther to the north than the 
northern limits of the Carboniferous limestones, and are spread 
out over the thinning and slightly inclined edges of these beds, 
and over the more disturbed and more highly elevated edges of 
be 
wider areas than the preceding formations of carboniferous lime- 
2, ‘ 
! i : ile i 1 solution 
8 view, sustained by facts, while it offers a general so 
of the difficulty momiind the non-occurrence of carboniferous 
e 
qualities of surface-on which the western coal measures rest, 
Prove conclusively that extensive denudation had taken place 
Previous to the coal period; and this fact should suggest a cau- 
fon in our conclusions regs ing the vast influence of modern 
denudation upon the surface of the globe. 
