CONTEMPORANEITY OF STRATA. 45 



different fossils, if one has been deposited by fresh water, 

 and the other has been laid down in the sea. The fresh- 

 water deposits of one period are obviously contemporaneous 

 with the marine formations of the same period, and they may 

 not be far removed from one another in point of distance, 

 but they must contain altogether different organic remains. 

 The former will contain remains of the fresh- water and ter- 

 restrial animals of the period, and of these only ; whilst the 

 latter will principally, if riot exclusively, be characterised by 

 the remains of marine forms of life. In this way, there is 

 some reason to believe, may be explained the differences 

 between the fossils of the Old Red Sandstone and of the 

 Devonian rocks, strictly so called. Both are believed to 

 have been deposited in the same geological period, and to be 

 truly " contemporaneous ; " but they do not contain the same 

 fossils. This may be readily explained, however, if we sup- 

 pose the former to represent the fresh-water deposits of the 

 Devonian period, or to have been laid down in an inland 

 sea, ^ whilst the latter is the true marine formation of the 

 same period. 



Under any circumstances, however, we must remember 

 that the doctrine of "homotaxis," if rightly limited and 

 defined, in no way diminishes the value of fossils as indica- 

 tions of the age of the formations in which they occur. If 

 we give the term "contemporaneous" a purely geological 

 sense, and endeavour to forget its literal signification as 

 applying to events which have occurred at precisely the same 

 moment of time, then it is just as good an epithet for the 

 different deposits belonging to a given geological formation 

 as is the term " homotaxeous." All the deposits which 

 possess Carboniferous fossils, at whatever point of the earth's 

 surface they may be situated, belong to the Carboniferous 

 period, and are therefore geologically contemporaneous. All 

 that is really implied by the doctrine of " homotaxis," rightly 

 regarded, is that we cannot say that any great formation in 

 any one country is the precise equivalent of the same forma- 

 tion in any country very widely removed in point of distance, 

 in the sense that its deposition began and ended at exactly 

 the same times ; and therefore we .cannot parallel the sub- 



