GEOLOGY OF THE ATLANTIC OCEAN. 193 



evolution — can not easily be isolated. I would recommend to those 

 biologists who discuss these questions to addict themselves to the 

 oyster. This familiar mollusk has successfully pursued its course and 

 has overcome all its enemies, from the flat-toothed selachians of the 

 Carboniferous to the oyster-dredgers of the present day, has varied 

 almost indefinitely, and yet has continued to be an oyster, unless in- 

 deed it may at certain portions of its career have temporarily assumed 

 the disguise of a Gryphaea or an Exogyra. The history of such an 

 animal deserves to be traced with care, and much curious information 

 respecting it will be found in the report which I have cited. But in 

 these respects the oyster is merely an example of many forms. Simi- 

 lar considerations apply to all those Pliocene and Pleistocene mollusks 

 which are found in the raised sea-bottoms of Norway and Scotland, 

 on the top of Moel Tryfaen in Wales, and at similar great heights on 

 the hills of America, many of which can be traced back to early Ter- 

 tiary times, and can be found to have extended themselves over all the 

 seas of the northern hemisphere. They apply in like manner to the 

 ferns, the conifers, and the angiosperms, many of which we can now 

 follow without even specific change to the Eocene and Cretaceous. 

 They all show that the forms of living things are more stable than the 

 lands and seas in which they live. 



If we were to adopt some of the modern ideas of evolution, we 

 might cut the Gordian knot by supposing that, as like causes can pro- 

 duce like effects, these types of life have originated more than once in 

 geological time, and need not be genetically connected with each other. 

 But while evolutionists repudiate such an application of their doctrine, 

 however natural and rational, it would seem that Nature still more 

 strongly repudiates it, and will not allow us to assume more than one 

 origin for one species. 



Thus the great question of geographical distribution remains in all 

 its force, and, by still another of our geological paradoxes, mountains 

 become ephemeral things in comparison with the delicate herbage 

 which covers them, and seas are in their present extent but of yester- 

 day when compared with the minute and feeble organisms that creep 

 on their sands or swim in their waters. The question remains, Has 

 the Atlantic achieved its destiny and finished its course, or are there 

 other changes in store for it in the future ? The earth's crust is now 

 thicker and stronger than ever before, and its great ribs of crushed 

 and folded rock are more firm and rigid than in any previous period. 

 The stupendous volcanic phenomena manifested in Mesozoic and early 

 Tertiary times along the borders of the Atlantic have apparently died' 

 out. These facts are in so far guarantees of permanence. On the 

 other hand, it is known that movements of elevation along with local 

 depression are in progress in the Arctic regions, and a great weight of 

 new sediment is being deposited along the borders of the Atlantic, 

 especially on its western side, and this is not improbably connected 

 TOL. xxx. — 13 



