366 D. C. DAYIES ON THE PHOSPHORITE 



Discussion. 



Prof. Seeley remarked that the concretionary character and dense 

 structure of the nodules were possessed by them in common with the 

 nodules in the Cambridge Upper Greensand ; and although the latter 

 nodules had no investing graphite, they often showed indications of 

 vegetable origin. He thought that Mr. Davies had laid too much 

 stress on the animal origin of the phosphate ; for the geological depo- 

 sits richest in fossils, such as Inferior Oolite or Cornbrash, do not 

 contain more than 3 or 4 per cent, of phosphate of lime ; and if its 

 origin was as supposed, we should expect phosphatic beds to 

 be much more numerous than they are in nature. The recent 

 researches in the ' Challenger ' have revealed facts which seem to 

 have some bearing on this question. Foraminifera in falling through 

 the water have their shells dissolved to some extent. Prof. Rogers, 

 by noticing that greensands were forming in warm streams in the 

 ocean, had rendered it probable that, while the process of solution 

 was going on, the silicate of alumina and iron was being redeposited 

 in other shells which had not yet fallen ; and in falling some of them 

 may become filled with phosphate of lime. This process might also 

 lead to the deposition of a gelatinous mass of phosphates on the sea- 

 bottom, which might ultimately be converted into the nodules. He 

 said that he had ascertained that most marine plants would yield a 

 considerable percentage of phosphate of lime, and he was therefore 

 more inclined to accept the view that the phosphate in these deposits 

 was due to vegetable organisms than to assign them an animal origin, 

 especially as a large accumulation of phosphates would result from 

 the growth and decay of banks of seaweed growing in one locality 

 during long periods of time. Still he thought there may have been 

 some unusual circumstances to lead to the formation of such deposits ; 

 and he had therefore argued in favour of there being an excess of 

 phosphoric acid in the sea at that time, due to the denudation of 

 apatite or other phosphatic matter of volcanic origin. 



Mr. Charlesworth did not agree with Prof. Henslow's views as 

 to the coprolitic nature of the phosphatic nodules, and was prepared 

 to accept the notion of their being redeposited from dissolved apatite. 

 The discovery of phosphatic beds in such early rocks as those of the 

 Bala series seemed to him to be of the highest interest. 



Mr. Hawkins Johnson observed that Dr. Pereira had shown that 

 there was about 7 per cent, of phosphate of lime in the ashes of sea- 

 weed, which might suffice to produce the phenomenon. 



Mr. Warington W. Smyth attributed the thin coating of graphite 

 to the presence of graphitic schists of considerable thickness at that 

 horizon. It was constantly the case that hard nodules, such as iron- 

 stones, presented the appearance of having undergone some rubbing 

 process which gave their surface a polished and striated appearance. 

 He therefore thought that these nodules had been aggregated together 

 much in the same way as the well-known nodules in Carboniferous 

 beds. 



Mr. D. Forbes was inclined to believe, with Mr. Seeley, that the 



