162 SEAS OF CARBONIFEROUS PERIOD. [CH. Ill 



Carboniferous formation, the persistence of characteristics 

 over large areas of the earth's surface is most striking. 

 The repetition of coals, sandstones and shales in the 

 Carboniferous rocks of the North American continent 

 and in that of Great Britain seems almost to point to a 

 common origin." And this is by no means the only 

 example that could be adduced of the closest lithological 

 analogies between contemporaneous rocks in widely sepa- 

 rated localities. 



These two series of facts almost seem to lead at once 

 to the conclusion that we have here evidence that in, say 

 the Carboniferous period, there was a tract of ocean con- 

 tinuous from east to west of not great depth, which would 

 point to adjacent land and set aside the theory that the 

 deep oceans of to-day have always been practically the same. 



But there are some criticisms to consider first. It has 

 been objected to the question of contemporaneity, let 

 alone the continuity, in a given formation that it is im- 

 possible strictly speaking, since organisms take time to 

 migrate. A given species comes into existence let us 

 suppose in the Australian district; it has to get to the 

 European seas where it may be also found ; the time that 

 elapses while this journey is made is longer or shorter ac- 

 cording to the distance and to the variety and difficulty 

 of the obstacles. " For anything that Geology or Paleonto- 

 logy is able to show to the contrary," wrote Prof. Huxley, 

 " a Devonian fauna and flora in the British Islands may 

 have been contemporaneous with Silurian life in North 

 America and with a Carboniferous fauna and flora in 

 Africa." 



