S 8 
PALAEONTOLOGY OF NEW-YORK. 
formation, that it is impossible at the present time to parallelize the 
deposits of these two regions of country. It is only by a considera¬ 
tion of the physical conditions of the period that we may arrive at 
some conclusion. 
From the gradual recession of the ocean to the southward during 
the deposition of these limestones, and the manner of their overlapping, 
it is evident that there is a certain degree of unconformity among the 
members of the series. This becomes more manifest when we carry our 
examinations into the Coal measures, which lie unconformably over all 
these limestones, except, perhaps, the upper one ; and also, to some 
extent, over the Devonian and Silurian rocks beneath. 
The recession, and the consequent unconformability, could only have 
resulted from a movement in the pre-existing land or sea bottom. 
Further evidences of such a movement are to be seen in the Cincinnati 
axis, which, extending from Canada to Tennessee, has elevated the 
lower rocks; and it may be that the movement producing this axis 
was initiated prior to the deposition of these limestones. 
Admitting this view of the subject, the elevation of that axis, or the 
subsidence of the sea bottom on the east and on the west, may have 
so far divided the waters that the sediments derived from the east 
were not carried beyond that line ; while to the west there may 
have been a quiet, shallow sea, fitted for the development of these 
faunas, and for the accumulation of the calcareous material forming 
this great series of limestones. This view may be sustained by the fact 
that nowhere, so far as I know, do the Carboniferous limestones appear 
beneath the Coal measures on the east of the Cincinnati axis, in Ohio 
or Kentucky. 
I regard this question as one open for investigation; and we shall k 
arrive at a true solution of the problem much sooner by studying the 
long lines of outcrop in the west, than by any discussion of probable 
physical conditions. It is a question of the highest interest for the true 
exposition of our geology. 
