BiaSBY PALEOZOIC ROCKS OF NEW YORK. 



269 



and New York, as far as at present known; it is hoped that 

 further details will be unnecessary. The fossil species of New 

 York, unlike some of those in Wales, are confined to few habitats, 

 — ^only one, Spirifer radiatus, being found in four beds. They are 

 plentiful in three, and still more common in two. Further research 

 may alter this. 



Table X. — Giving a Convparative View of the Divergents of 

 Wales and of New York. 



Fossils. 



Wales. 



New York. 



Total 

 Species, of 



known 

 Habitats. 



Divergents. 



Total 



Species, of 



known 



Habitats. 



Divergents. 



Plantse 



12 

 25 

 69 

 81 

 41 

 154 

 167 

 22 

 64 

 57 

 12 

 11 

 50 

 11 



1 



8 



9 



30 



18 



70 



114 



11 



35 



34 



10 



8 



26 



6 



33 

 11 

 49 

 81 

 67 

 61 

 225 

 44 

 49 

 94 

 23 

 8 

 96 



2 



2 



3 



6 



10 



13 



18 



4 



10 



10 



3 



2 



10 



Annelida 



Crinoidea 



Zoophyta 



Bryozoa 



Crustacea 



Brachiopoda 



Monomyaria 



Dimyaria 



Gasteropoda 



Heteropoda 



Pteropoda 



Cephalopoda 



Pisces 





Total 



776 



380 



841 



93 





/. Recurrence. — The transition from the subject of " divergence " 

 to that of " recurrence," or the vertical range of life, is easy and 

 natural. We shall treat of the latter first as found in the Silurian, 

 and secondly in the Devonian, system of the State of New York and 

 Wales. 



It is hoped that the statements which follow will not be destitute 

 of interest. They rest mainly on two published tables : — Table I., 

 Quart. Journ. Geol. Soc, vol. xiv. p. 399 ; and the Table of the Si- 

 lurian Fossils of Britain, in Appendix A, in Sir Roderick Murchison's 

 ' Siluria,' 2nd edition. 



Throughout these pages, the word " recurrence " will be used in 

 the sense of reappearance in one or more epochs. It was introduced, 

 I believe, by our present learned President, to whom we owe many 

 of our happiest geological expressions. " Vertical range " is another 

 phrase used to denote progress from epoch to epoch. Not to recur 

 renders any given form typical, or " restricted " in the language of 

 James Hall ; and thus it becomes of high value, as denoting a certain 

 geological period: but typical fossils are not marked, as far as I 

 know, by great structural differences. All the orders, and many of 

 the genera, contain numerous examples of both typical and recurrent 

 life. Still distinctions may be pointed out. Animals, especially 



T7 2 



