PHOSPHATES IN THE CAMB1UAN KOCKS. 373 



is found to be in exact proportion to the animal remains present 

 —being in the proportion of less than j per cent in those which 

 contain but few remains, and as much as 4 per cent in the richest 

 beds. This, however, is only found to be true in regard to the beds 

 which have not undergone any metamorphic change by contact 

 with or proximity to intrusive dykes ; for the beds which in this 

 section yield the largest proportion of phosphoric acid are so altered 

 in another section, from contact with an intrusive mass, that 

 scarcely a trace of this ingredient is left in them, though fossils are 

 there in plenty as impressions, but with none of their structure 

 left. In this section, also, a similar change has taken place in the 

 character of the beds near to the trappean masses. For some distance 

 below and above the trap, the beds show an altered character : 

 instead of being grey, hard, flaggy, and calcareous-looking, as are 

 the other beds in the section, they gradually become black and 

 slaty in character, and have a distinct slaty cleavage near the 

 dykes. About a foot from the trap there is a very rich line of 

 fossils, in which the large Paradoxides Davidis occurs plentifully ; 

 but here none of the structure of its thick shell is left, and its 

 arched character is gone, the impressions being flattened and dis- 

 torted. An analysis of portions of this bed where the fossils are 

 most plentiful shows an almost entire absence of phosphoric acid 

 and of lime, whilst these ingredients ought, according to the evidence 

 derived by the analyses of other beds in which this fossil occurs, to 

 have been present in large proportions. 



When I made my first analysis of this rock I felt much puzzled at 

 the absence from it of P 2 5 ; and on mentioning the result to one or 

 two chemical friends I was assured by them that it must be there, and 

 that it would be found in combination with some other base, if not 

 with lime. On repeating my analysis, however, with every care, I 

 could not find it in any quantity ; and I then placed portions of the 

 rock, with the impressions of the fossil upon them, in the hands of 

 Mr. Hughes and Mr. Hudleston, telling them at the same time of 

 the opinions expressed. The result obtained by Mr. Hughes from 

 the altered rock was phosphoric acid 0*096, equivalent to tribasic 

 phosphate of lime 0*209 ; whilst another piece of rock unaltered, 

 with Paradoxides Davidis, the same fossil, upon it, gave phos- 

 phoric acid 3*00, = tribasic phosphate of lime 6-54, or thirty 

 times as much as in the altered bed, showing an extraordinary 

 difference, and one which can only be accounted for by supposing 

 some chemical change to have taken place sufficient to have set free 

 the P 2 3 from this rock. Mr. Hudleston's analysis also gave very 

 much the same result, being only in the proportion of 0*11 per cent 

 of P 2 5 in the rock near the trap. The carbonate of lime, which 

 was also determined by Mr. Hughes to be present in the proportion 

 of 42-39 per cent, in parts of the unaltered rock, has also dis- 

 appeared almost entirely from the altered slate. There can be no 

 doubt, I think, that the phosphoric acid occurs in the unaltered 

 rock in the state of tribasic phosphate of lime ; and as this is known 

 not to undergo a change from any amount of heat applied to it by 



