Ill CLASSIFICATION OF THE ROCKS 



in rely from the authority of the observations, whicli have been made ap to this time. 

 What may be discovered hereafter, we can noi know; but it is righl to draw inferences 

 up to the present time : it is necessary only thai we Bhould keep ourselves read] to change, 

 or alter our views with the progress of discovery. 



The introduction o( mollusca, then, begins with the New-Yoi k bj Btem : e^ en a) its base, 

 the Potsdam Bandstone, the Lmgula abounds. In the previous system, plants and worms 

 abounded; but it is worthy of observation that we have noi yel discovered land plants, 

 nor with certainty any terrestrial animals : all the organic bodies are marine. 



The base, then, of tin- 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 

 m inner 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- 

 formahly apon 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, r<>is upon diversity of organic remains. In order, however, that 

 the foundation for the two systems Bhould stand upon sufficient evidence, it is essential 

 that those remains Bhould be quite dissimilar in their types : such is found to be the case. 

 In tin did Red system, fish possessing peculiar characters prevail ; while most, if not all 

 the mollusca <■!' the New-York Bystem, disappear. In New-York, however, there is a ^reat 

 wain 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 Bystem, 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 : 

 I therefore di-miss 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 ibis, 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 heme 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 

 di\ is 



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 folle 



"Murchison's Silurian System, p. 196, section 22. 



