332 W. H. HUDLESTON ON THE CHEMICAL 



Casein too, in coagulation, will carry down about 6 per cent of calcic 

 phosphate in the presence of free acid. This latter fact is adduced 

 to show that a slightly acid condition of the bottom-water and of 

 the fluids in the pasty mass which is the embryo of the future for- 

 mation may be deemed essential to the production of phosphatic 

 nodules. 



The second portion of Mr. Hicks's paper opens up a larger and 

 far more difficult question, viz. as to how far an intrusion of 

 trap may deprive a sedimentary bed of phosphoric acid. In the 

 ease he adduces (see Analysis No. II.) it is clear that a Trilobite-bed 

 in contact with a trap is more or less deficient, as compared with 

 other Trilobite-beds of the same series, in phosphoric acid, which 

 presumably may have been there. The rock is also very poor in 

 lime, containing not quite one half per cent, of its entire mass, as far 

 as this can be dissolved by acids. The absence of the extractive 

 matter alluded to in the analysis No. I. also points to considerable 

 alteration, as does the carbonized condition of the organic matter in 

 the slate, and the almost total absence of pyrites in the body of the 

 slate, whilst great plates of this mineral occur in some instances 

 along its junction with the trap. 



It seems reasonable to suppose that this particular bed may not 

 always have been so poor in phosphate in comparison with the other 

 Trilobite-beds of the series ; and if it is always found that these 

 beds, though showing the form of the Trilobite, yet contain in 

 the vicinity of the trap but little phosphate, it is a legitimate in- 

 ference that the trap must have had something to do with this dis- 

 appearance. 



But of course there is nothing new or extraordinary in a trap or 

 any other intrusive or igneous rock taking up and appropriating to 

 itself portions of the rocks through which it passes. This is easy 

 enough to understand, as far as the portion of sedimentary rock which 

 is actually received and incorporated into the substance of the in- 

 vading mass is concerned. The difficulty is, to make out by what 

 process certain substances in the adjoining sedimentary beds, not so 

 incorporated, can have been transferred to the body of the trap itself. 

 In this case, for instance, it will be asked by what means has the calcic 

 phosphate been removed from the altered slate and transferred to 

 the trap, as is alleged to have been the case. It will be remembered 

 that the core of the trap contains at least three times as much phos- 

 phoric acid as the Trilobite-bed through which it passes ; whilst the 

 exterior of the trap, according to Mr. Hicks's analysis, contains a 

 still greater proportion. 



The chemical geologists, with Bischof at their head, are by no 

 means in favour of the isolation of phosphorus, " which would involve 

 complicated operations, the conditions requisite for which are not 

 likely to occur in the chemistry of geology." Indeed calcic phosphate 

 resists decomposition by heat better than most salts. There can be 

 little doubt, however, that the contact of igneous rocks with sedimen- 

 tary beds does in some degree extract the phosphates from these 

 latter. 



