CONTEMPORANEITY OF STRATA. 15 



not exactly contemporaneous, but that they succeeded one 

 another in point of time, though by no long interval geologi- 

 cally speaking. 



Most of the facts bearing upon this question rnay 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 Brachiopods 

 belonging to the genus Produda 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 existence of an ocean 

 embracing all these points, and, in spite of its enormous ex- 

 tent, so uniform in temperature, depth, and the other condi- 

 tions 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 uni- 

 formity 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 destruc- 

 tion 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 pro- 

 bable 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 Carboniferous 

 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 existed. On the 

 contrary, the deposition of the Carboniferous Limestone must 

 have first taken place in one comparatively limited area say 

 in Europe where fitting conditions were present both for the 

 animals which characterise it, and for the formation of beds of 

 its peculiar mineral and physical characters. How wide this 

 area may have been, signifies very little. It may have been as 



