1867.] 



' Thesaurus Siluriciis.' 



S77 



locality on the nature and amount of life, in the same way as we observe 

 at the present time. As each region yields up its fauna to the collector, 

 much of that fauna is found to be new, the bond of connexion with other 

 Silurian districts being in great measure generic. 



The physical conditions of sea and land being necessarily local, pro- 

 duced as they are from time to time by agencies limited in space, the 

 dwellers among these conditions must in a certain measure be local too, 

 and typical — subject at any moment to removal. The first, occupants of 

 any spot who shall point out ? 



The maximum of life, meaning by that expression the largest combina- 

 tion of abundance, variety, and rank, is local. It may take place at the 

 beginning of a stage, or of an epoch, in the middle, or at the end, being 

 governed principally by the nature of the sediment. The rich Primordial 

 beds of Western Newfoundland and of Quebec, the crowded Pleta beds of 

 Russia and of Esthonia, the Trenton Limestone of America, the Mid-Silu- 

 rian rocks of Bohemia* {E. e. 1, 2), some of those of Wales, the Lower 

 Helderberg group of New York, are conspicuous examples of this. Parts 

 of the Llandovery stage of Wales and of New York (U.S.A.) present a 

 great dearth of life, and for a well-known reason. How barren are the 

 vast accumulations of Lower Silurian in Bolivia, as at present believed ! 

 The Potsdam Sandstone of the valleys of the St. Lawrence and the Missis- 

 sippi shows no signs of life for hundreds (and perhaps thousands) of square 

 miles, save in small oases peopled chiefly by Lingulae in incalculable mil- 

 lions of individuals. 



Nearly equal areas of Central North-east America (N. latitudes 50°-32°) 

 and Europe may have received about the same attention ; but the latter, 

 so far, has proved the richer by above a thousand species, as we see in the 

 subjoined Table C. 



Table C. — Known species of America and Europe compared. 



Orders. 



Plante (kingd.) 



Amorphozoa 



Foraininifera 



Annelida , 



Hetero-Pteropoda .... 

 Polyzoa (Bryozoa) .... 

 Ccelenterata (Zoophyt.) 



Crinoids 



Cystidea 



Sedis incerte 



Species. 



America. 



56 

 58 



'*36 



96 

 203 

 262 

 193 



56 

 4 



964 931 



Europe. 



20 

 61 

 25 

 98 

 144 

 177 

 245 

 93 

 63 

 2 



Orders. 



Carried forward 



Asteriadte 



Crust /Trilobites ... 

 ■ [ Entomostraca 



Bracliiopoda 



Monomyaria 



Dimyaria 



Gasteropoda 



Cephalopoda 



Pisces 



America, 



964 



29 

 396 



75 

 678 



78 

 181 

 421 

 321 



9 9 



3145 4325 



Europe, 



931 

 29 

 1008 

 170 

 721 

 56 

 241 

 271 

 861 

 34 



* The extraordinary abundance of Trilobites, Cephalopoda, &c. here is accounted for 

 by the beds being calcareous and overlain by trappose masses, in place of the sand and 

 gravel more commonly seen. 



