198 DEVONIAN SYSTEM, 



VI. THE UPPER ROCKS OF NEW-YORK EQUIVALENT TO THE DEVONIAN 

 SYSTEM OF ENGLAND AND THE CONTINENT. 



Mr. Conrad was the first American geologist who perceived the equivalency of the upper 

 New-York rocks, to those which were descrihed by Mr. Phillips under the name of Devo- 

 nian. To him also is to be given the credit of identifying the Silurian system with the 

 lower rocks of this State. When the outlines of resemblance have been traced, it requires 

 only diligence and moderate capacity to fill up the details. While it is admitted, however, 

 that the New- York and Silurian rocks have been proved by American geologists to belong 

 to a coeval period, it is not proved that the two are identical. Such a closeness of agree- 

 ment, in such distant rocks, could not be expected. This much seems to be established, 

 namely, that the rocks of the two continents, limited upwards by the Coal series, and by 

 the Taconic system below, were deposited during the same period ; but whatever of a mo- 

 difying nature existed in either continent, had its influence on each series respectively. 

 A prolongation of a particular deposit beyond the corresponding one of a distant continent, 

 often took place. Intercalated members appear in a few instances. Organic beings were 

 formed on the same types, but rarely identical. While resemblances were preserved in the 

 greater nuiuber, the novelties were rarely common. As New-Holland must have her 

 kangaroos, and ([uadruped-like forms in her aviaries ; the Galapagos, their lizard forms ; 

 and Africa and America, each their pecidiar faunas ; so analogy forbids our expectancy 

 that the faunas of oiu- two silurian worlds should be identical. It is not a variety, however, 

 which arises from necessity, from obedience to physical causes : the variety exists for 

 variety's sake, and to fill creation with diversified grades of being. 



The advancement of geology in this country received a new impulse, when its cultiva- 

 tors began to study our rocks independently of European formations. So long as investi- 

 gations were directed towards identification v/ith foreign rocks, just so long our own for- 

 mations remained unknown to us, perhaps from the want -of proper characters by which 

 they could be made out. The study of fossils has, in later years, been followed by a real 

 progress in the science of geology ; and this has arisen, not so much from the use of fossils 

 as characteristics, as from an independence which they gave to the thoughts and methods 

 of observers. They gave us the power to compare oiir rocks with each other at distant 

 points, and to work out our system on a basis which is truly American, and which has 

 really created an American geology. This result has been practically of great value here, 

 in addition to tlic confirmation of leading principles which had preceded it abroad. Wo 

 have now our Silurian and Devonian systems sufficiently well defined to answer all the 

 ends of science. The work of accurately identifying strata may go on, now that correct 

 outlines have been marked out, and (fur great landmarks are so well defined. 



