294 



Royal Society :- 



or at the end, being governed principally by the nature of the sedi- 

 ment. 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-Silurian 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 Llan- 

 dovery 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. Law- 

 rence and the Mississippi shows no signs of life for hundreds (and 

 perhaps thousands) of square miles, save in small oases peopled 

 chiefly by Lingulce in incalculable millions 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. 



The Cephalopoda, Crustacea, Brachiopoda, and Annelida of 

 Europe appear to largely exceed in number of species those of North 

 America, while in nine Orders (see Table C) the two hemispheres 

 hold nearly equal quantities. America greatly surpasses Europe in 

 the number of its Crinoids, and to a smaller extent in Plantae and 

 Gasteropoda. I am not prepared with any inference from these 

 facts. We know that the mineral constitution, and the past external 

 influences in these several parts of the earth are diff'erent — not that 

 the first is as influential as has been supposed. 



Many species are marked as undefined in the ' Thesaurus,' because 

 they are often only known by sin pie fragments. 



About a thousand species have never been seen but in one locality. 



* The extraordinary abundance of Trilobites, Cephalopoda, &c. here is ac- 

 counted for by the beds being calcareous and overlain by trappose masses, in 

 place of the sand and gravel more commonly seen. 



