CONTEMPORANEITY OF STRATA. 39 



temporaneous, but that they succeeded one another in point 

 of time, though by no long interval geologically speaking. 



Most of the facts bearing upon this question may be elicited 

 by a consideration of such a widely extended and well-known 

 formation as the Mountain Limestone or Sub-Carboniferous 

 Limestone. This formation occurs in localities as remote 

 from one another as Europe, Central Asia, North America, 

 South America, and Australia ; and it is characterised by an 

 assemblage of well-marked fossils, amongst which Brachio- 

 pods belonging to the genus Product a may be specially 

 singled out. Now, if we believe that the Carboniferous 

 Limestone in all these widely distant localities was strictly 

 contemporaneous, we should be compelled to admit the ex- 

 istence of an ocean embracing all these points, and, in spite 

 of its enormous extent, so uniform in temperature, depth, and 

 the other conditions of marine life, that beings either the 

 same or very nearly the same inhabited it from end to end. 

 We can, however, point to no such uniformity of conditions 

 and consequent uniformity of life over any such vast area at 

 the present day; and we have therefore no right to assume 

 that this is the true explanation of the facts. Indeed this 

 explanation would almost necessarily lead us to the now 

 abandoned theory that each period in geological history was 

 characterised by a special group of organisms spreading over 

 the whole globe, and that there took place at the close of 

 each period a general destruction of all existing forms of life, 

 and a fresh creation of the new forms characteristic of the 

 next period. 



In our inability, then, to accept this view, we must seek 

 for some other explanation of the observed facts. The most 

 probable view, and the one which is supported most strongly 

 both by what we see at the present day and by what we learn 

 from numerous examples in past time, is this : The Carbon- 

 iferous Limestone was not deposited all over the world in 

 one given period, by one sea, or at exactly the same time ; 

 so that it cannot be said to be strictly " contemporaneous " 

 wherever it is found. This would imply a uniformity of 

 conditions over vast distances, such as exists nowhere at the 

 present day, and such as we have no right to assume ever 



