3oi ILLOGICAL GEOLOGY. 



an assumption contrary to probability. The probability ia, 

 that the causes which have changed Faunas have been locai 

 rather than universal; that hence while the Faunas of 

 some regions have been rapidly changing, those of others 

 have been almost quiescent ; and that when such others 

 have been changed, it has been, not in such ways as to 

 maintain parallelism, but in such ways as to produce diver- 

 gence. 



Even supposing, however, that districts some hundreds 

 of miles apart, furnished groups of strata that completely 

 agreed in their order of superposition, their mineral charac- 

 ters, and their fossils, we should still have inadequate proof 

 of contemporaneity. For there are conditions, very likely 

 to occur, under which such groups might differ widely in 

 age. If there be a continent of which the strata crop out 

 on the surface obliquely to the line of coast — running, sa}-, 

 west-northwest, while the coast runs east and west — it is 

 clear that each group of strata will crop out on the beach 

 at a particular part of the coast ; that further west the next 

 group of strata will crop out on the beach ; and so continu- 

 ously. As the localization of marine plants and animals is 

 in a considerable degree determined by the nature of the 

 rocks and their detritus, it follows that each part of this 

 coast will have its more or less distinct Flora and Fauna. 

 What now must result from the action of the waves in the 

 course of a geologic epoch? As the sea makes slow inroads 

 on the land, the place at which each group of strata crops 

 out on the beach will gradually move towards the west : 

 its distinctive fish, mollusks, crustaceans, and sea-weeds, 

 migrating with it. Further, the detritus of each of these 

 groups of strata will, as the point of outcrop moves west- 

 wards, be deposited over the detritus of the group in ad- 

 vance of it. And the consequence of these actions, carried 

 on for one of those enormous periods required for geologio 

 changes, will be that, corresponding to each eastern stratum. 



