BIGSBY PALEOZOIC ROCKS OF NEW YORK. 



267 



the proportion of " divergents" there to the whole of the Inverte- 

 brata of which the sedimentary position is known is only about 

 one-ninth, — eighty being in two beds, ten in three, and one in four 

 beds : the Diinyaria, Gasteropoda, and Crustacea are the most 

 divergent; Crinoidea and Zoophyta the least so. But this, I feel per- 

 suaded, is an inadequate estimate of the true '^ divergence " of this 

 American area, although the best attainable at present ; for the more 

 complete examination of the same or equivalent system in the Welsh 

 area shows a far larger number of divergents, — 779 species changing 

 their habitats 382 times — a condition of things, we may note, which 

 bespeaks great vital force. 



Table IX. — Exhibiting the Number of Beds into which the Silurian 

 Fossils of Wales diverge from their first or original habitat. 



Fossils. 



i 



^ 1 



Number of Beds into which Divergence takes 

 place. 



^ 



X 



IX 



YIII 



VII 



VI 



V 



IV 



III 



II 



J 1 Total 

 Diverg. 



Brachiopoda ... 



Crustacea 



Dimyaria 



Gasteropoda ... 



Zoophyta 



Cephalopoda . . . 

 Bryozoa 



167 

 154 

 64 

 57 

 81 

 50 

 41 

 22 

 12 

 69 

 25 

 11 

 11 

 12 



1 



T 



3 



2 



i* 



] 

 1 



[ 



L 



2 

 1 



i' 

 i 

 "i" 



2 

 5 



'3' 

 1 



1 



i 



1 



i' 



15 

 5 



1 



"'2 



2 

 1 

 1 



"i 



17 

 4 

 1 

 1 

 3 

 3 

 1 



"i 

 1 



"i 



19 

 15 

 5 

 10 

 3 

 4 

 2 

 4 

 2 



"1 



22 



16 

 7 

 5 

 6 

 6 

 5 

 1 

 3 

 3 

 3 

 2 

 1 

 1 



31 

 21 

 21 

 15 

 12 

 9 

 8 



113 

 70 

 35 

 34 

 29 

 25 

 18 



2 

 3 



1 

 2 



T% 



4 



T 

 I 

 3 



1 

 11 



\ 

 2 



T3- 



1 



3 

 2 

 3 



1 

 12 



Monomyaria . . . 

 Heteropoda . . . 

 Ecliinodermata 



Annehda 



Pteropoda 



Pisces 



i\ 11 

 3 11 



51 9 



2| 8 



4' 8 



6 7 



1 



Plantae 



Total 





776 



2 



6 



2 



6 



15 



28 



33 



65 



81 



144| 379 





Table IX., which is here introduced, will show the extraordinary 

 number of beds occupied by the same species, — a circumstance 

 which becomes of great import when we remember that these beds 

 represent certain depths of water, and that therefore the batho- 

 metrical zones of life were not so strictly adhered to in Silurian 

 times as at present, although their limits are even now loosely and 

 variously defined. A rather high and equably diffused temperatuie 

 then permitted the animals to wander into different depths, and to 

 rest at any spot which supplied their several needs. One half, 

 at least, of the Invertebrates were predacious, and therefore in some 

 measure independent of the flora, which must have changed wth 

 the sediment ; and, on inquiry, we discover that the freest and most 

 numerous divergents are carnivorous, namely the Cephalopoda, 

 Heteropoda, Crustacea, and certain Zoophyta and Brachiopoda. 

 This Table follows the animal life of the period into its greater 



VOL. XY. PAET I. U 



