370 



H. HICKS ON THE OCCTTRKENCE OF 



8. The shell of Paradoxides Damdis, a 



fossil of large size, with as little 

 matrix as possible. 



9. The shell of P. Davidis with a 



little matrix attached. 



10. Lingula-flags with Lingulella Da- J 



visit from Whitesand Bay, St. V 

 David's. J 



11. Lmgula-flags with Hymmocaris\ 



from near Dolgelly, North I 

 Wales. j 



12. Tremadoc rocks, with some Trilo- \ 



bites, but with a great abundance | 

 of Brachiopods and Lamelli- I 

 branchs, from Ramsey Island, 

 St. David's (carbonate of lime in 

 considerable amount). 



13. Lower Arenig rocks from White- 



sand Bay, St. David's, with 

 Grraptolites, &c. 



14. Middle Arenig rocks from White- 



sand Bay, with Trilobites in con- 

 siderable abundance. 



15. Upper Arenig rocks from near 



Abereiddy Bay, with a few Tri- 

 lobites, Grraptolites, &c. 



P 2 O g per cent. 

 2000 



17-05 



0-50 



060 

 1-50 



025 



From 0-50 to 1 50, in 

 proportion to the 

 amount of fossils 

 present. 



0-35 



H. Hicks. 



W. H. Hudles- 

 ton. 



H. Hicks. 



H. Hicks. 



H. Hicks. 



H. Hicks. 



H. Hicks. 



The analyses show that, of these very early rocks, those which 

 appear to contain no animal remains have, as might be expected, 

 the least proportion of phosphoric acid, that the rocks in which 

 the Brachiopoda or Graptolites occur alone do not contain any 

 very large proportion of that ingredient*, and that the rocks which 

 contain the remains of Crustacea have invariably the largest amount 

 of phosphoric acid. The Lingula-flag beds which were examined 

 contained only Brachiopoda ; and the proportion of P 2 5 in them 

 was therefore small. The Tremadoc rocks, made up in great 

 part of the shells of Brachiopoda, but with many Crustacea in 

 addition, contained it in larger quantities ; while the beds of the 

 Menevian, containing little else than Crustacea (which occur there 

 in great abundance), showed a marked increase in the amount 

 present. 



From these facts it is natural to infer that the Crustacea were the 

 chief cause of the presence of so much phosphoric acid in these early 

 deposits, and that the Mollusca were considerably inferior to the 

 Crustacea in their power of producing this ingredient. For the 

 purpose of testing this fact I made analyses of the fossil shells of 

 several of the Mollusca ; and, with the exception of the Brachiopods 

 Lingula, Bisdna, and Obolella, which have more or less of a horny 

 texture, but are of small size in these early deposits, I find that the 



* The so-called horny shells of the Brachiopoda contain P 2 O- in considerable 

 quantity. Prof. Sterry Hunt found as much as 85*79 per cent, of phosphate of 

 lime in the shell of Lingula ovalis ; but in these early rocks the Brachiopoda 

 are of small size, and do not occur in very great abundance ; so the beds in 

 which they oocur alone are not usually rich in this ingredient. 



