REMARKS OX MR. DAKWJNS THEORY. 



185 



proved by the small horizontal extent of the various deposits which 

 make np a formation, and which generally extend further in propor- 

 tion to the fineness of the sediment of which they are composed. I 

 think, therefore, that even taking into consideration submarine 

 volcanos, we may safely conclude that no deposition is going on now 

 over at least one-fifth of the area of the ocean. 



In the present state of the globe about one-fourth of its surface is 

 land : if we add to this one-fifth of the ocean we have two-fifths of 

 the surface of the globe on which no deposition is taking place ; and 

 when we think that deposition could never have been universal, but 

 that there must always have been large areas of denudation, we may 

 feel sure that this is not very far from the truth. We may therefore 

 conclude that the periods of repose in any one area are to the periods 

 of deposition in about the ratio of two to three. 



We now know that the deep sea is inhabited ; and if we suppose 

 that on equal areas the average number of the inhabitants of the shallow 

 sea are to those of the deep sea as eight to one, and to the inhabitants 

 of the land as one to three and a half — both suppositions may, I think, 

 be safely made — we find that the number of the inhabitants of the 

 areas of repose are to the number of the inhabitants of the areas of 

 deposition as three is to two. It therefore follows that at least one-half 

 of the animals and plants live in places where their remains can only 

 be very rarely preserved. And this calculation will apply also to the 

 ancient world ; for if the present ratio of land to water, viz. one-third, 

 should not be the average we should still arrive at very nearly the 

 same conclusion ; for if it should be greater, it is evident that the 

 ratio of the inhabitants of the areas of repose to those of the areas of 

 deposition would be increased ; if, on the contrary it should be less, 

 the land would be more divided into islands, with of course a larger 

 coast line and larger areas of shallow sea ; but the supply of sediment 

 from the land would also be reduced and many parts of the shallow 

 sea, which if near a continent would be areas of deposition, will near 

 an island be areas of repose, while at the same time they will be, 

 perhaps, more thickly inhabited. 



But even where deposition is taking place, the burying of organic 

 remains in all deposits but limestone is perhaps the exception, and not 

 the rule. For if the deposition is rapid vegetable life, and conse- 

 quently animal life, cannot flourish. If on the contrary it is slow, all 

 bodies must lie for a long time uncovered on the bed of the sea, while 

 there all the soft parts will either be eaten or decay, and the rest, 

 subjected to the action of the tides or currents, which are generally 

 found where deposition is going on, will often be broken, worn down, 

 and destroyed. 



From these considerations we must infer that the number of organic 

 remains imbedded bears but a small proportion to those that have 

 lived. But even after having been safely imbedded, the chances are 

 much against a fossil ever finding its way into the cabinet of a 

 collector. If buried in sand it is almost sure to be destroyed by the 

 percolation of water, and all trace of it removed ; and in any case it 

 VOL. iv. x 



