ANALYSES' OF SOME CAMBRIAN ROCKS. 379 



For the purpose of instituting a comparison, the following analyses 

 of lobster were also made : — 



Lobster-shell dried at 100° C. contained of per cent, 

 phosphoric anhydride 3*26 



Lobster with shell weighing 566 grms. con- 

 tained 4*3 grms. of phosphoric anhydride, 

 equal (on the entire weight) to 0*76 



This rate would give to a ton of boiled lobster, with the shell, 

 about 17 lbs. phosphoric anhydride. 



Lobster-flesh (boiled), calculated on the entire 



weight, contained 0*332 



As these two latter analyses were not calculated upon the substance 

 dried at any definite temperature, they cannot be deemed to have 

 any scientific value, so far as the actual percentage of phosphoric 

 acid is concerned ; but as rough experiments showing the amount 

 of phosphoric acid which a dead Crustacean buried in sediment might 

 be expected to yield in proportion to its weight, these analyses may 

 be of geological interest. The second analysis would seem to indi- 

 cate that a lobster would contribute phosphoric acid (anhydride) 

 equal to about f- per cent, of its total weight. The shell contains 

 far more in proportion. A .French chemist some years ago gave the 

 following analysis (Fremy, Annal. Ch. Phys. 3, xliii.). 



calc. phos. calc. carb. org. mat. Total. 



Sea crab 6*7 49-0 44-3 100 



Land crab .... 6-7 56-8 36-5 100 



The amount of calcic phosphate agrees pretty well with that found 

 in the lobster ; and it is rather singular that, according to the analysis 

 quoted, whilst the carbonate of lime varies so materially in the sea 

 and land crab, the calcic phosphate is the same in both. 



Reasoning from the analogy of existing Crustacea, therefore, one 

 would say that about 3 per cent, of phosphoric acid (anhydride) 

 might be expected to have existed in the shell of the ancient Trilo- 

 bite, unless the shell, as suggested by Mr. Hicks, had a somewhat 

 different composition, and that the very great excess of phosphoric 

 acid which some of these Trilobites exhibit in the fossilized condition 

 is due to the ordinary processes of substitution, when, as in the 

 pseudomorphs of mineralogy, one salt replaces another more or less 

 completely in the fossil. In this case the excess of phosphoric acid 

 now found in the shell of these Menevian Trilobites would be derived 

 in part from the phosphoric acid once existing in the flesh of the 

 animal itself. From the same source also, viz. the flesh of the 

 animal, would be derived the sulphur which now, in the form of 

 pyrites, is so much associated with the phosphatic matter of these 

 beds. 



It is evident, then, that there exists a considerable amount of 

 phosphoric acid in certain portions of the Cambrian rocks ; moreover 

 this is associated with the large Trilobites in a remarkable manner. 



