474 Transactions. 



calcium-phosphate, and the process would then have extended 

 itself upwards. As we find the phosphate above and the car- 

 bonate below, it is tolerably certain that the process is extend- 

 ing itself downward, and is due to descending solutions. 



4. Basalt Theory. — That the deposits were formed in situ 

 by the deposition of P 2 5 from descending waters which derived 

 their P 2 5 from the basalt. I do not think it possible that the 

 overlying basalt could have supplied the P 2 5 necessary. No 

 phosphorus-bearing mineral was detected in the microscopic 

 examination, and micro-chemical tests likewise failed to reveal 

 the presence of any such mineral. 



5. Limestone Theory. — That the deposits were formed bv 

 the deposition of P 2 5 from percolating waters which derived 

 their P 2 5 from the limestone. It is certain that the phosphoric 

 acid was derived from the limestone. We have seen that organic- 

 remains rich in phosphorus are found in the latter, and that, 

 moreover, a small amount of phosphate is distributed through- 

 out its mass. I think that a deposition from waters is in part 

 responsible for the formation of the phosphate, but that it is 

 subordinate and subsequent to a concentrating action. 



6. Concentration Theory. — That the deposits were formed by 

 the concentration of the phosphatic contents of the limestone, by 

 the weathering action of waters containing carbonic and per- 

 haps other organic acids, which dissolved out the calcium-car- 

 bonate of the limestone, but left behind the much less soluble 

 calcium-phosphate. 



7. Combination Theory. — That the process just outlined was 

 followed by the deposition of P 2 5 from percolating waters which 

 had leached out their P 2 5 from the limestone. The mode of 

 weathering of the limestone at the Millburn quarry lends a great 

 amount of support to this view. The surface of the limestone 

 is carved out into a number of deep " guts," leaving lofty pin- 

 nacles and overhanging shelves of limestone — an appearance 

 which at first suggests a striking unconformity with the brown 

 sands which fill the depressions. The sculpturing, however, is 

 abnost wholly if not entirely due to chemical erosion. 



On the outer parts of the pinnacles, where exposed to wind 

 and rain, the limestone has in many places weathered to a crumbly 

 brownish sandstone, containing comparatively a small percent- 

 age of CaC0 3 . Along the laminae the weathering has progressed 

 more quickly. Isolated " floaters " of limestone are found in the 

 middle of the brown sands ; they are blocks of limestone which 

 have offered great resistance to the weathering process, and are 

 now entirely surrounded by clays and sands, in the midst of 

 which, still horizontal, they seem to float. A sample was taken 

 from the interior of one of these floaters, where it was least 



