114 
CLASSIFICATION OF THE ROCKS 
merely from the authority of the observations which have been made up to this time.. 
What may be discovered hereafter, we can not know ; but it is right to draw inferences 
up to the present time : it is necessary only that we should keep ourselves ready to change, 
or alter our views with the progress of discovery. 
The introduction of mollusca, then, begins with the New-York system : even at its base, 
the Potsdam sandstone, the Lingula abounds. In the previous system, plants and worms 
abounded ; but it is worthy of observation that we have not yet discovered land plants, 
nor with certainty any terrestrial animals : all the organic bodies are marine. 
The base, then, of the New-York system, is clearly marked ; but the outgoing of it, the 
limits superiorly, are far more obscure. In this State, it is certainly not marked by re¬ 
markable changes in the sediments, or by powerful disturbance of former beds, in such a 
manner as to create unconformability between the newest members of the New-York and 
the oldest members of the succeeding systems, so as to cause the latter to repose uncon- 
formably upon the former. So in Wales,* the upper Ludlow rocks crop out from beneath 
the old red sandstone (Red system) conformably. The distinction, then, between the 
systems in both cases, rests upon diversity of organic remains. In order, however, that 
the foundation for the two systems should stand upon sufficient evidence, it is essential 
that those remains should be quite dissimilar in their types : such is found to be the case. 
In the Old Red system, fish possessing peculiar characters prevail ; while most, if not all 
the mollusca of the New-York system, disappear. In New-York, however, there is a great 
want of fossils of any kind, except some obscure plants : the fish are confined to a thin 
mass ; but time may bring to light a greater abundance of the peculiar forms of the Old 
Red system, by which it will be more perfectly identified with the same formation in 
Europe. We may recur to this subject again when I have reached the Old Red system r 
I therefore dismiss it for the present. 
§ 2. Classification - of the new-york rocks. 
The New-York system, then, comprising as it does a series of great thickness, and con¬ 
sisting of numerous members, it becomes important that we should adopt some mode of 
subdividing it. In doing this, I find that the divisions heretofore proposed meet all the 
necessities of the case ; besides, they have been approved of by those who are acquainted 
with the New-York rocks, and hence I shall retain the division adopted in the reports. It 
is admitted that they are geographical ; still they will be found useful geologically, as in 
each of the divisions we find rocks allied to each other, rather than to those in the other 
divisions. 
The New-York system admits of four divisions, and it gives to each of these divisions 
the name of the particular region in which they are found. In the ascending order, the 
divisions stand as follows : 
Murchison’s Silurian System, p. 196, section 22. 
