50 Parallelism of the Palaozoic Deposits 



folding and raising the terrestrial crust, gave birth to the chain of 

 the Alleehanies. The manner in which the plications, largely 



undulated at first, contract, multiply and fold over in going from 



northwest to southeast, towards the metamorphic and granitic 

 rocks, situated most frequently beyond the chain, properly so 

 called, has been perfectly elucidated by the two Professors Rogers.* 

 It does not enter into our design further to extend this notice ; 

 having fulfilled, according to our ability, the end which we pro- 



posed, to establish a parallel between the palaeozoic formations of 

 North America and Europe. Permit us, in conclusion, to present 

 a resume of the course we have followed, and the principal re- 

 sults at which we have arrived. 



In order to make fully understood the interest and importance 

 of this parallelism, and the light which it throws upon the knowl- 

 edge of palaeozoic deposits in general, we have shown the advan- 

 tageous geological conditions of North America, and how, owing 

 to the horizontality of the beds over great extent of surface, to 



their concordant and uninterrupted superposition, it is possible to 

 arrive at an absolute certainty as to the duration of species, that 

 is to say, the point in the series where they first appear and 

 where they become extinct. 



In order to compare North America with Europe, it has been 

 necessary for us to give a rapid glance at the groups and stages of 

 which the palaeozoic formation is there composed. The differ- 

 ences which are presented to us in the geognostic conditions of 

 the state of New York and the Western States, such as Ohio and 

 Indiana, have revealed to us the degree of importance which it 

 is necessary to attach to these different groups. We have seen 

 that their number, variable according to their vicinity or distance 

 from lands emerged at the epoch of their formation, had little 

 importance as regards the establishment of systems founded upon 

 palseontological characters. We have seen also, that in general, 

 the limestones are more constant than the shaly or arenaceous 

 beds, that they form more extensive horizons, and furnish a surer 

 guide to the geologist, f 



Passing afterwards to a comparison of the two continents, we 

 have shown, supporting our views by geological analysis, how 

 the American substages should be grouped to correspond with the 

 Silurian, Devonian and Carboniferous systems of Europe. We 

 have not disguised the fact that the divisions introduced upon 



* On the Physical Structure of the Appalachian Chain as exemplifying the laws 

 which have regulated the elevation of great mountain chains generally, by VV. B. 

 and H. D. Rogers. 



t M. C. Prevost, in his memoir upon the synchronism of formations, (Comptes 



Rendus, April, 1845,) has clearly shown the importance of the pelagic calcareous 



deposits as compared with the arenaceous beds formed under the influences of 

 coasts. 











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