OF GEOLOGICAL FORMATIONS. 229 



Reference to the annexed diagram, where D represents a Devo- 

 nian area, say, in Europe, S a Silurian one in America, and C a 

 Carboniferous one in Africa all contemporaneous will render this 

 point more intelligible. Now, on the proposition above stated, 

 reasoning from our present knowledge of the antiquity of faunas, 

 and accepting the doctrine of migration, as maintained by Professor 

 Huxley and others, to account for the possible contemporaneity of 



D 



distinct faunas, it may be assumed that S (or America) will receive 

 its Devonian fauna from D ; D (Europe) its Carboniferous from C ; 

 and C (Africa) a later fauna from some locality not here indicated. 

 In other words, migration, as indicated by the arrows, would set 

 in from D to 8 ; one from (7 to D; one from 8 to some possibly South 

 American Cambrian locality, and one, bringing a Permian or some 

 later-day fauna, from an unknown locality towards C. "Were this 

 order of migration to continue here, or at other portions of the 

 earth's surface, in this or in a similarly consecutive manner, the 

 results obtained would be in perfect consonance with the facts pre- 

 sented by geology. But is there any reason whatever for the con- 

 tinuance of this order of migration ? Surely no facts that have as 

 yet been brought to light argue in favour of a continued migration 

 in one direction. Why, then, it might justly be asked, could not 

 just as well a migration take place from /S to J9, and impose with 

 it a Silurian fauna upon a Devonian ? What would there be to 

 hinder a migration from $ to (7, placing the American Silurian 

 fauna upon the Carboniferous of Africa ? Why has it just so hap- 

 pened that a fauna characteristic of a given period has invariably 



