GEOLOGY. 235 



Lick, which have been ground by the trampling of the large 

 pachyderms and ruminants which frequented that swamp. Some- 

 times these nodules do not make up more than a considerable 

 fraction of the bed, the remainder being sand, pebbles, or the 

 marl of the character found on the bed beneath. Again, the 

 nodules are so crowded in the bed that they are soldered together 

 into one mass, with scarce any interspaces between the separate 

 concretions. 



"Mingled with the concretions there is found a very variable 

 quantity of fossil vertebrate remains ; by far the greater part of 

 these consist of exceedingly worn fragments of cetacean bones 

 and sharks 1 teeth and vertebrae, both clearly of the same species 

 as those found lower down in the marls in the same section. 

 Mingled with these, but comparatively rarely found, are the bones 

 of a fossil horse, pig, mastodon, and bones and utensils of man. 

 These last-named fossils are almost always in a state of preserva- 

 tion, widely different from that of the remains of the cetaceans 

 and selachians with which they are mingled. Their appearance 

 indicates a comparatively recent inhumation. 



"Chemical analysis shows us that the nodules of this deposit 

 contain the greatest quantity of phosphate, of lime, the quantity 

 varying at different points from 40 to nearly 70 per cent. The 

 first and most natural seeming explanation of the large amount 

 of this salt is, that it is derived from the bones and excrements of 

 the animals whose remains are found in the bed. But the points 

 where the most bones are found are not those where the phos- 

 phate deposit is thickest or richest. At Chisholm's Island, on the 

 waters of St. Helena Sound, where the bed has the greatest de- 

 velopment yet discovered, and where the analysis shows more 

 phosphoric acid than at some of the localities the richest in bones, 

 the remains of vertebrate animals are very rarely found. It is 

 not too much to say that at this locality not 1 part in 10,000 of 

 the mass is composed of vertebrate remains. Nor can we assume 

 that the mass of phosphoric acid has been furnished by the decay 

 of bones which have been utterly broken down ; in that case we 

 should have the remaining bones showing all degrees of preser- 

 vation. This, however, is not the case; the fragments, though 

 usually much worn, retain their structure very well. Although I 

 went upon the ground with a disposition to regard the beds as the 

 result of the decay of vertebrate remains, the general character 

 of the deposit soon compelled me to seek some other explanation 

 of its oriirin. 



^j 



1 It has been suggested by a distinguished chemist, that the 

 deposit was the result of the submergence of a great guano area, 

 during which submergence the bones of marine animals became 

 mingled with the mass. There are several objections to this 

 view: in the first place, no remains of birds have been found in 

 the deposit, though fossils quite as likely to be destroyed are well 

 preserved there. Then it is difficult to see how in the immediate 

 past this swampy shore could have been the breeding-place of the 

 quantities of birds which would have been required to have accu- 

 mulated these phosphates, nor could we suppose that the climate 



