464 Transactions. 



5. The grains of the sandstone are identical in character 

 with those of the top band of limestone at Mllburn quarry. On 

 dissolving away the calcium-carbonate of the limestone in cold 

 dilute HC1, and on examining the residue, the quartz-grains of 

 both limestone and sandstone are seen to be similar — the same 

 shape, the same size, the same colour. Glauconite-grains occur 

 in both. The sandstone contains much more limonite than the 

 limestone, but that is to be expected on the supposition of its 

 subsequent cementation with iron-oxide. 



6. The brown sandstone often contains a small amount of 

 lime-phosphate ; often, too, as at the Millburn Company's 

 phosphate-workings, grains of sand are cemented together by 

 lime-phosphate to form a poor-grade rock-phosphate (25 "87 

 per cent.). Let us assume that the sandstone is a Lower Ter- 

 tiary deposit, and this fact will lead us into difficulties. It 

 is not probable that the sandstone would originally be phos- 

 phatic, for it contains no fossils ; and a sedimentary rock, if 

 phosphatic, has derived its phosphate of lime from the numerous 

 animals which inhabited its seas. The limestone contained 

 many fossils, and also a small amount of phosphate, disseminated 

 through it, as has been shown above. The basalt, which lay on 

 top of everything else, contained no phosphate. The sandstone 

 then, containing no phosphate, lay then above the limestone, 

 which alone could supply it. To-day we find that the sand- 

 stone does contain phosphate. How did it acquire it ? The 

 percolation of water has been downward, and away from the 

 sandstone ; there has been no upward percolation of water, 

 nor has there been any other means of transferring the calcium- 

 phosphate : and yet the sandstone has received a certain amount 

 from the limestone. The extreme difficulty of accounting for 

 this fact suggests that, after all, perhaps the sandstone did not 

 originally lie above the limestone. 



There is no exposure of rocks in the district which shows 

 the contact of sandstone with either basalt or limestone — a 

 contact which would probably throw great light on the ques- 

 tion as to whether the sandstone is an original or a secondary 

 formation. But the reasons given above make me of the opinion 

 that it would probably support my view if it did exist. 



Rock-phosphate. 



Character. — The rock-phosphate is an amorphous nodular 

 deposit, found either in pockets on the upper surface of the 

 limestone, or, where the latter is absent, on top of the under- 

 lying glauconite sands. When the limestone is present we 

 always find the masses of rock-phosphate separated from it by 



