GENERAL ACCOUNT OF THE DEPOSITS. 13 



the Upper Jurassic rocks when these beds were being denuded by 

 the work of the Neocomian waters. The evidences of this are 

 plainly written upon the nodules themselves, they being to a great 

 extent the mutilated remains of Mollusca of Oxfordian, Kimme- 

 ridgian or Portlandian species. This being the case one naturally 

 searches these formations for such a supply of Phosphatic nodules 

 as might furnish an accumulation of 'coprolites' like that of the 

 Upware deposit. Now phosphatic nodules do occur in the Kim- 

 meridge clay, as indeed is the case with most of our Mesozoic 

 clays, but they are everywhere very few in number, and the great 

 majority of the Jurassic fossils are not phosphatised at all, this 

 condition being most exceptional. We therefore at once meet 

 with a difficulty in the way of such a theory. Moreover if the 

 phosphatic nodules had been derived, just as they are, from the 

 older rocks, we might reasonably expect that the nature and quan- 

 tity of the phosphate of lime would vary in regular recurrence 

 according to the deposit from which the species was derived, 

 whereas we find that this is not the case. The general character 

 of the phosphate of lime nodules is similar, whether it has come 

 from the Oxford clay, Kimmeridge clay, Portlandian rock, or from 

 the older Neocomian itself, and again nearly all the derived fossils 

 are found in the condition of phosphatic casts. It is therefore my 

 belief that although the phosphatised nodules and fossils were 

 derived from older rocks, yet the phosphatic matter itself was all, 

 or nearly all, of one age, namely contemporaneous with the deposit 

 in which we now find them, that is Neocomian. 



In the words of Mr Walker the "phosphatic nodules had been 

 formed of clay [marl and limestone] soaked in decomposing animal 

 and vegetable matter" and saturated with phosphates. And such 

 is the theory adopted by Mr Teall in his Essay (p. 39) \ A simi- 

 lar case is that of the Ashley phosphates of South Carolina which, 

 according to MM. Holmes^ and Leidy^, are sands and clays of 



1 The formation of the Cambridge Greensand coprolites, which are very 

 different, has been very fully treated of by Prof. Bonney, in his Cambridgeshire 

 Geology, p. 63, but I have long had suspicion that the amount of phosphate 

 has been increased since they left their bed in the gault, because the nodules in the 

 gault are generally softer and appear less rich in phosphate of lime. 



^ The Vertebrate Rocks of S. Carolina, by F. S. Holmes, A. M. Charlestown, 1870. 



^ "Vertebrate Kemains, chiefly from the Phosphate Beds of South Carolina." — 

 Joum. Acad. Nat. Sci. Philadelphia. Vol. viii. part 3. 



i 



