GEOLOGICAL CONCLUSIONS. 351 



This is the only method by which any thick stratum of lime- 

 stone could be made out of a single set of species, for all 

 such species have a narrow range in depth ; and the only way, 

 from any succession of species, if those species are alike in 

 range of depth. 



In the case of existing coral reefs, there is yet no evidence 

 that the species of the lower beds differ from those of the top. 

 There is also no evidence, in any part of any ocean, that there 

 is a set of cold-water corals fitted to commence a reef in deep 

 water and build it up to such a level that another set of 

 species may take it and carry it up higher ; the facts thus far 

 gathered are all opposed to such an idea. Should it be here- 

 after proved that the corals of the inferior beds differ in 

 species from those now existing, it will probably be found that 

 the predecessors of those now living were also shallow-water 

 species ; so that the subsidence in any case was necessary. 



V. DEEP-SEA LIMESTONES SELDOM IF EVER MADE FROM CORAL 

 ISLAND OR REEF DEBRIS. 



This point has been discussed on pages 143, 211. The facts 

 show that the sediment or debris from a shore is almost wholly 

 thrown back by the waves against the land where it originated, 

 or over its submerged part in the shallow waters, and that it 

 is not transported away to make deep sea formations. 



The facts have also a wider bearing, for thev teach that 

 lands separated by a range of deep ocean cannot supply one 

 another with material for rocks. The existence of an Atlan- 

 tic ocean continent — an Atlantis — has sometimes been assumed 

 in order to make it a source of the mud, sand and gravel, out 

 of which the thick sedimentary formations of the Appalachian' 

 region of North America were made. But if this Atlantis 

 were a reality, there would still have been needed, in addition 



