BIGSBY — PALAEOZOIC ROCKS OF NEW YORK. 397 



20. In New York the species of fucoids occupy and are typical of 

 only one group. 



21. All the individual existences are perfect at once, from the 

 earliest dawn of life, in their organization and social relations. 



22. It is a great thought, that throughout the incalculably long 

 succession of fossiliferous deposits, palaeozoic or more modern, all 

 animal and vegetable life was constructed upon the same idea of 

 innervation, organs of sense, supply and waste, fecundation, &c. 



23. There is another kind of life- centre — the geographic, belong- 

 ing to one and the same group. This forms numerous separate 

 provinces linked together by a few common fossils, and displaying 

 extraordinary variety. This principle or regulation is carried out 

 abundantly everywhere. Bohemia and Scandinavia have scarcely a 

 Silurian fossil in common. One-half of the Russian and Irish fossils, 

 and two-thirds of those of New York, are new and peculiar. Even 

 the east and west sides of the small districts in Wales and England 

 investigated by Prof. Phillips differ remarkably in their population. 

 We see this in the American Tertiaries and in the recent seas. 



24. Contrary to the opinion of Mr. D. Sharpe, the mollusc having 

 the greatest vertical range has the greatest horizontal extension, 

 being found in the most distant regions. 



25. There is no evidence of multiplication of species by transmu- 

 tation. 



26. Fossils may be contemporaneous in geological age, without 

 being contemporaneous in time as commonly understood. 



Geological age is partly determined by fossil evidence. Now, the 

 presence of living beings (subsequently fossil) depends on mineral 

 and other conditions, such as temperature, depth, currents, &c, 

 which were nowhere the same for large spaces, but were always 

 undergoing changes from plutonic and other causes — changes always 

 more or less local and limited, the deposits being thick or thin in 

 places : so that the universal scheme of palaeozoic life was not 

 everywhere worked up to the same point ; here preparations were 

 making for Lower Silurian deposits, — there for the Upper, or De- 

 vonian, and so on. Thus isochronism was perhaps not common. 



27. The principles of recurrency, succession, increment, and rela- 

 tive abundance of fossil species are the same in New York, Wales, 

 and elsewhere, modified by local circumstances. 



28. Recurrency, or reappearance in different strata, is at the 

 same time the measure of viability in the species, and of connexion 

 in the groups of strata. It is a kind of living nexus, pointing out 

 that the groups belong to one and the same order of things. It may 

 have been partly caused by migration. 



Recurrency is not so common in New York as in Wales, — in other 

 words, vertical range is longer in Wales. Great depth is an ob- 

 stacle to the existence or transmission of living creatures. 



29. Everywhere, on the eastern as well as on the western con- 

 titinent, the same fossils, of all orders and kinds, appear in the same 

 succession. A very few Crustacea and a Lingula or Obolus or two, 

 amid a dense matting of fucoids, appear at what now seems to be the 



2 d 2 



