UNIFORMITY OF COMPOSITION 123 



The essential nature of the rock, or the organic 

 remains of which it is composed, was found to be the 

 same throughout ; the soft material met with between 637 

 and 748 feet, which superficially resembles chalk, and the 

 hard rock from 748 feet to the bottom, not differing in 

 this respect from the rest, the hardness in the one case 

 being due to cementation by crystalline deposit, and the 

 softness in the other to decomposition. 



The chemical investigation of the core by Dr. C. G. 

 Cullis and Dr. E. W. Skeats prove it to possess a re- 

 markable purity. It consists almost entirely of the car- 

 bonates of lime and magnesia ; of material insoluble in 

 acids there was no more than from O'OOl to 0'083 per cent., 

 and of calcium phosphate from 0*136 to 0'288per cent. There 

 is thus a remarkable absence of all such sediments as 

 may be derived from ordinary soil (terrigenous sediment) . 

 The two carbonates were present in various proportions, 

 from the surface down to 637 feet (except between 15 and 

 20 feet) the magnesium carbonate amounts to only 1 to 5 

 per cent., but from this depth to the bottom the quantity 

 is much greater, for the most part as much as 40 per cent. 

 In the exceptional case referred to, between 15 and 20 

 feet, the amount is 16 per cent. 



A vast quantity of other important work was carried on 

 by the members of the second and third expeditions, 

 which included Professor David, and Messrs. Sweet, 

 Halligan, and Finckh, but for an account of this the 

 original report may be consulted. We must now content 

 ourselves with such citations as are necessary to our 

 argument. 



The material obtained from the boring, together with 

 other specimens which might be expected to throw light 

 on the problem of the formation of the reef, were sent 

 to Professor Judd in London, who had the solid core 

 prepared for study by slicing it longitudinally through 



