INTRODUCTION. 
7 
the fossil characters, we have little evidence of any great physical change. 
In the State of New-York, the Chazy limestone, which succeeds the 
Calciferous sandstone, often presents in its lower divisions evidences of 
a continuation of the same conditions as prevailed during the deposition 
of the preceding rock. The lithological aspect of some of the beds is 
precisely similar to that of the Calciferous sandstone, showing that the 
waters charged with the same materials still flowed over the ocean bed of 
the Chazy period. Nevertheless in some other localities within New-York 
there appears a slight unconformity between the Calciferous sandstone and 
the succeeding rock ; but this appearance may be attributed to the absence 
of a portion of the limestone beds, permitting the Birdseye limestone to 
rest directly upon the sandstone. 
In the northwest, on the contrary, there are many evidences of physical 
change. There, the Calciferous sandstone is often, through a thickness of 
forty or fifty feet or more, a huge mass of breccia. The materials of the 
rock appear to have been broken up, while partially indurated; the in¬ 
terstices are often filled with sand; and fragments of friable sandstone, 
from the weight of an ounce to several pounds, are found mingled with 
the broken rock itself. In some instances these fragments of sandstone 
present lines of deposition, and sometimes of discordant lamination, 
showing that they have been torn from masses of rock previously in¬ 
durated. These phenomena occur at several points along the Mississippi 
river; and however local they may be in their extent, they point to a 
disturbed condition in the surrounding ocean, which must have been highly 
unfavorable to the continuance of the previously existing fauna. 
From the circumstance that these conditions of the rock have been 
noticed only in the west, we are prepared to find the source of disturbance 
in that direction, and probably beyond the limits to which our examina¬ 
tions have extended. 
It should not be forgotten, moreover, that at the west, and throughout 
the great exposure of the Calciferous sandstone in the Northwestern States, 
it is everywhere succeeded by a homogeneous light-colored sandstone, 
