384 Brief Account of the ^ Thesaurus Siluricus.' [Feb. 21^ 



Table F. — Geographical Summary of Silurian Life. 



Ord-Crs. 



J 



o 





.2 



ustralia. 



1 

 g 



•uouii 









o 









<j 













4 





M 







B 

















56 



20 













Tibet. 







62 



63 







"1 



"1 



"6 



To America 



and Europe. 







25? 













Not definite! V anp.Rnted, 































2 





27 



To America 



and. Europe. 





193 



93 



... 





2 





6 





>> 





oo 



oo 







20 





3 





9) 







29 











1 







36 



98 







1 



... 



7 





>> 



I . r TTi'lnT-iifna 



396 



998 



10 





11 





30 



Various. 





^ ?>. -i Phvllnnnrlfi "1 



^ L V/ Is LI clLUU-d) J 



77 



170 











5 







Polyzoflr 



203 



177 



2 





20 





23 



Various. 





Brachiopoda 



678 



r21 







It) 





0.3 



Various. 





Monomyaria 



78 



56 







2 





5 



To America 



and Europe. 





181 



241 



'3 





8 



19 



12 





Pteropoda & Heteropoda 



103 



145 



1 





3 



1 



15 





5J 



Gasteropoda 



421 



274 



9 





9 



13 



10 







Cephalopoda 



321 



861 



5 







8 



16 





» 







34 



















4 



2 



















3156 



4305 





... 



100 



43 



231 





3156+4305=7461 species. 



Geograjphical Distribution of Silurian Life, 



The * Thesaurus ' tends to show that North America, east of the Ptocky 

 Mountains, may probably be divided into two areas, — the one to the north 

 of 57° (or of Lake Superior) being chiefly Upper Silurian, resting on crys- 

 talline rocks, the one to the south of that line, down to the Gulf of 

 Mexico, on the contrary, being fully developed in some part of this great 

 space. 



It exhibits the regrettable fact that Asia, Africa, and Australia, taken 

 together, have hitherto yielded only 200 species of Silurian remains; but 

 this arises from the absence of exploration. 



I have not yet had opportunity to bring together, harmonize, and com- 

 pare the Silurian life of the several countries of Europe. The accom- 

 plishment of such a task might produce some definite truths, and many 

 more probabilities. Either this vast region would prove to be one great 

 Silurian area, with barriers here and there, and v/ith certain channels of 

 communication, and to be the result of many operations throughout a 

 long interval of time ; or it might turn out that the Silurian deposits and 

 their fossils occupy three separate areas : — (1) the Britanno- Scandinavian, 

 which has all the three stages, and the Primordial ; (2) the Bohemian, at 



