520 
GEOLOGY OF THE FOURTH DISTRICT. 
tinctions, the better able are we to seize upon obscure relations at distant points, and turn them 
to our advantage in the identification of strata. We have learned that a formation which on 
the Mississippi is a limestone, is, on the Hudson, a shale and sandstone ; yet in the former 
place we may detect some obscure traces of slate and sandstone, while in the latter we often 
meet with beds of impure limestone. The same or similar changes occur in other formations. 
In the names adopted thus far, there is nothing to prevent the formation of a harmonious 
nomenclature for all our rocks; while to the inhabitant of New-York, and other States, the 
local names with which he has become familiar may be retained and used without detriment 
to the progress of the science. 
