214 GEOLOGICAL DISTRIBUTION. 



tionship which binds together the more ancient forms of life. The 

 Brachiopoda, however, offer partial examples of this kind, more 

 particularly the family Terebratulidae, and, where but a compara- 

 tively limited persistence is demanded, such instances are by no 

 means rare. 



Geographical Distribution. In comparing the past with the 

 present distribution of life upon the globe, one cannot fail to note 

 a well-marked difference. Broad distribution appears to have 

 been far more prevalent in the early period of the earth's history 

 than now, and argues strongly for a predominance of more uni- 

 form conditions. Thus, if we take the class Brachiopoda by way 

 of illustration, we find that of some one hundred and thirty-five 

 recognised species and varieties living in our modern seas, there 

 is scarcely a single species which can be said to be strictly cosmo- 

 politan in its range, although not a few are very widely distrib- 

 uted, and, if we except boreal and hyperboreal forms, but a very 

 limited number whose range embraces opposite sides of the same 

 ocean. On the other hand, if we accept the data furnished by 

 Richthofen 67 concerning the Chinese fossil Brachiopoda, we find 

 that out of a total of thirteen Silurian and twenty -four Devonian 

 species, no less than ten of the former and sixteen of the latter 

 recur in the equivalent deposits of Western Europe ; and, further, 

 that the Devonian species furnish eleven or nearly fifty per cent, of 

 the entire number which are cosmopolitan, or nearly so. Again, 

 of the twenty-five Carboniferous species North America holds fully 

 fifteen (or sixty per cent.), and a very nearly equal number are cos- 

 mopolitan. The evidence furnished by the fossils of the Arctic 

 regions is equally conclusive in this direction. Not only are the 

 vast majority of species of Paleozoic (Silurian and Carboniferous) 

 fossils of the far north identical with forms occurring in the de- 

 posits of both temperate North America and Europe, but many of 

 them are distinctive types of formations which have been recognised 

 in almost all parts of the earth's surface where such formations have 

 been themselves identified. Thus, among the fossils obtained by 

 the officers of the late Polar expedition under command of Sir 

 George Nares, Mr. Etheridge 68 has identified Atrypa reticularis (Si- 

 lurian) and Productus semi-reticulatus and P. costatus (Carbonifer- 

 ous), the first from Cape Hilgard, in nearly the eightieth parallel 

 of north latitude, and the last two from Fieldeu Isthmus, latitude 



