198 DEVONIAN SYSTEM. 



VI THE l"IM>ER ROCKS OF NEW-YORK EQUIVALENT TO THE DEVONIAN 

 SYSTEM OF ENGLAND AND THE CONTINENT. 



Mr. Conrad was the fire! American u r «"l' >iri-i who perceived the equivalency of the upper 

 \ Fork rocks, t>> those which were described by Mr. Phillips under the name of Devo- 

 nian. To liim also is to be [riven the credit of identifying the Silurian system with the 

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

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

 thai the New-York and Silurian rocks have been proved by American geologists to helong 

 to a coeval period, it is nol proved that the two arc identical. Such a closeness of agree- 

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

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

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

 difying nature existed in either continent, had its influence on each Beries 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 Dumber, the novelties were rarely common. As New-Holland must have her 

 kangaroos, and quadruped-like forms in her aviaries; the Galapagos, their lizard forms ; 

 and Africa and America, each their peculiar faunas 3 so analogy forbids our expectancy 

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

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

 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 with foreign rocks, just so long our own for- 

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

 they could lie 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 fossil- 

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

 of observers. They gave us the power to compare our 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 the confirmation of leading principles which had preceded it abroad. We 

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

 ends of science. The work of accurately identifying strata may go on, now that cot!' 

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



