BIGSBY PALJEOZOIC ROCKS OF NEAV YORK. 289 



forgotten, that in the comparatively easy wanderings on the same 

 epochal horizon migration was probably neither frequent nor ex- 

 tensive. So at least we are taught by Troost as to the State of 

 Tennessee, by our President, Professor Phillips, in England, and by 

 Barrande in "Bohemia. " For," says Barrande*, '' we should expect 

 that on a surface so limited as that of Bohemia (60 by 15 miles 

 in its greatest dimensions) the fauna would be distributed uniformly ; 

 but it is not so. This basin presents, on a small scale, the same 

 absences or inequalities of distribution which we remark on a large, 

 over the whole globe, whether at the present day or in palseontolo- 

 gical times. The Trilobites, in particular, here have their principal 

 residences, occasionally only a few square-yards in extent ; and thus 

 they seem few until these centres of diffusion are discovered." But 

 migration is a true agency. The escape of a single individual into an 

 upper bed may people with its descendants many epochs and districts. 

 Angelin, Pictet, D'Orbigny, and Agassiz coincide in opinion -svith 

 the great authorities just named, and afSirm that species did not 

 reside in more than one palseozoic epoch or platform, or as mere 

 exceptions which, according to Agassiz, become more and more 

 rare with the progTess of palseontological knowledge. Angelin 

 absolutely meets with no specific form which passes from one to 

 another of his seven local stages or regions. In the first volume of his 

 * Contributions to the Natural History of the United States,' p. 104, 

 Agassiz broadly announces the axiom, " that facts exhibit the simul- 

 taneous creation and simultaneous destruction of entire faunae" in 

 the palseozoic ages, — and this, in minor periods or subdivisions (p. 

 96), accompanied by a coincidence between these changes in the 

 organic world and the great physical changes of the earth. But it 

 appears to other observers, fiilly as competent as the honoured men 

 just-named, that recurrency or vertical range is a fact which occurs 

 in a large number of fossils in aJmost every horizon, the very number 

 (scrupulously ascertained) being far too great to allow of the plea of 

 constantly mistaken identity. The voluminous and highly esteemed 

 writings of James Hall are full of instances of recurrence, established 

 by himself, and for the moment by him forgotten. We see from Table 

 XII., that they are 280 in number. Daniel Sharpe, one of our most 

 acute palaeontologists, witnesses to the same effect. Prof. H. D. 

 Eogers, of Glasgow, gives similar testimony for Pennsylvania ; and 

 M. De Yemeuil states authoritatively that the same fossil species are 

 scattered through the palaeozoic systems of America at different 

 levels. This is in the resume of his Parallel between North America 

 and Europef. His remarks on the palaeontology of Russia are 

 completely in the same sensej. Yertical range in fossil species 

 prevails to so great an amount in Wales and the adjacent counties 

 (Murchison and Morris), that it unites into one epoch strata lately 

 considered separate ; and it is even more remarkable in the eastern 

 districts so well described by our present President. The experience 

 of General Portlock in Ireland tends in the same direction. In Bar- 



* Syst. Sil. Boheme, p. 290. t Bull. Soc. Geol. France, 2 ser. vol. iv. 



\ Geol. Trans, n. s. vol. vi. p. 334. 



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