BIGSiSr PALEOZOIC ROCKS OF NEW YOUK. 285 



not thus restricted, but recurrent, the same species may be found in 

 the Silurian, Devonian, and Carboniferous systems; and this in- 

 volves a duration inconceivably protracted. The shortness of specific 

 life is more apparent than real, because all the epochal subdivisions 

 occupied long intervals of time ; and thickness, therefore, all other 

 things remaining the same, becomes a measure of longevity in 

 species. Where the thickness was great, and where the chemical 

 and mineral nature of the sediment and the sea was favourable (the 

 latter having a suitable depth and temperature), there was great 

 length of species-life, and, as a consequence, great geographic dif- 

 fusion. We see this very distinctly in the Upper Silurian of New 

 York, Wales, and Bohemia. Palaeozoic genera were not often long- 

 lived. Of the 192 found in the Silurian rocks of New York, 124 are 

 never seen out of their original rock-group ; 23 enter only into one 

 newer group; 14 into two; 7 into three; a Trilobite (Calymene) 

 into 5 newer ; an Atrypa {A. reticularis) into 9 groups ; with a few 

 other genera scattered. These remarks apply to the fossil organisms 

 of Wales. Out of 228 genera occurring there, 149 never leave 

 their first position ; 44 appear twice, 24 three times, 9 four times, 

 and 2 in five epochs, according to the General Table in the second 

 edition of Sir E. Murchison's ' Siluria.' It is not possible to com- 

 pare the viability of the faunae of these two basins very closely, be- 

 cause they are not exactly the same ; but where they are so, we are 

 pleased to see the poor and the prolific genera to be the same in 

 both, — vindicating a degree of mutual organic representation in these 

 two widely separated basins. 



§ 7. Epochal and Geographical Diffusion of Species. — The following 

 reflections present themselves on a survey of processes so ancient and 

 prolonged as those which laid down the palaeozoic strata of New York. 

 It is only on vast continents such as America, that the complete un- 

 broken whole of a grand geological conception like the central palaeo- 

 zoic basin of the United States can be seen and grasped. In smaller 

 spaces, as in islands, the idea becomes fragmentary, its beautiful rela- 

 tions are submerged, and much of the lesson is lost. These conceptions 

 are not like those of man, cogitated, modified, laboured at for an hour, 

 a year, or a life-time. The omnipotent Creator requires no period 

 of hesitation and contrivance; all is execution through inconcei- 

 vable extensions of time. His operations are ubiquitous, with all 

 their parts coordinated. A great formula is being worked out by a 

 predetermined series of processes, both simple and complicated, in 

 all parts of the globe. New existences have peopled the successive 

 groups of strata, partly by direct creation, and partly by migrations, 

 the latter occasioned and facilitated by never-ceasing agencies, plu- 

 tonian and neptunian. Fossils may be contemporaneous in geological 

 age without being contemporaneous in point of time as time is com- 

 monly understood. Geological age is in great measure determined 

 by the evidence of fossils. Now the presence of certain races (sub- 

 sequently fossil) depends on inconstant conditions, mineral, meteoro- 

 logical, and oceanic, on the accidents of plutonic action, and on 

 the varying thicknesses of deposits (so small in Scandinavia, and so 



