WALC07T] CORRELATION. 417 



The fact that the Paleozoic formations of America during the appearance and dis- 

 appearance of three successive faunas, which despite some common species are on the 

 whole well distinct, teaches us that the extinction and appearance of beings on the 

 earth's surface are by no means determined exclusively by the physical revolutions 

 of the crust, but are ordered and regulated by the laws of animal creation itself. 

 Still, it is not my intention to follow out this consideration, as it would lead me too 

 far. I merely wished to mention this, in passing, as a subject for further study, and 

 to point out to investigators that paleontology leads to the establishment of a geo- 

 logic chronology, independently of the more or less local revolutions which the fossil- 

 iferous strata have undergone since their deposition. 1 



From a study of the faunas of the two countries he considered that 

 the first, second, and third faunas of Bohemia are to be identified in 

 America ; that there exist manifold relations in all classes of animals of 

 the Upper Silurian division of the United States and Bohemia ; that, 

 in the first volume of HalPs Paleontology of New York, on the Lower 

 Silurian division, from the Potsdam sandstone to the Hudson River 

 group inclusive, he recognizes the First Silurian fauna of Bohemia, 

 Sweden, and England ; that the presence of the long-missed first fauna 

 of Bohemia in America has been demonstrated in a very satisfactory 

 manner by Owen in his discoveries in the northwestern United States ; 

 and that the occurrence of this fauna in the State of Georgia is indi- 

 cated by a Conocephalus brought to England. In conclusion, he says : 



Hence I am now perfectly convinced that the Silurian formations of North Amer- 

 ica, as well as those of the old continent, contain a succession of three different faunas, 

 which, on being separately compared with the latter, are seen to consist of the same 

 geologic elements and to follow each other in the same order. When I say that they 

 consist of the same geologic elements you know already that I am far from wishing 

 to maintain identity of species. I rely on other more general analogies which to me 

 are not less convincing. This is not the place to explain this more in detail, as that 

 would lead me too far ; but you will find here and there in my work some passages 

 which express my view of the matter. In admitting and recognizing in all Silurian 

 regions of the two continents three general faunas corresponding and equivalent to 

 each other, I am induced by the facts to pronounce a further result of my investiga- 

 tions, namely, that the local divisions of strata containing these great faunas, though 

 greatly differing from each other in each region of a certain extent, are not equal to 

 each other in the various countries, especially when the countries are far apart, geo- 

 graphically. This truth seems to me solidly established by a multitude of facts 

 which are tabulated and compared in my geologic sketch, and is confirmed in a very 

 satisfactory manner by the facts mentioned in volume 2 of J. Hall's Paleontology of 

 New York. 2 



Rogers. — In a paper read before the British Association for the Ad- 

 vancement of Science in 1856, on the correlation of the North American 

 and British Paleozoic strata, Prof. Henry D. Rogers described the 

 Paleozoic section of the Appalachian region and that of. England, and 

 instituted comparisons between them, to show the parallelism of the 

 North American and European Paleozoic rocks. 3 He says : 



In attempting this correlation it should be remembered that nature represents no 

 true or literal equivalency of strata, nor anything closer than a mere approximate 



1 Op. cit., p. 339. * Op. cit., p. 345. 



3 On the correlation of the North American and British Paleozoic strata. British Assoc. Adv. Sci., 

 vol. 26, 1857. Trans. Sec, p. 184. 



Bull. 81 27 



