Andrew. — On the Clarendon Phosjihaie-deposits. 475 



weathered ; it was partially analysed, as also was a sample of 



absolutely fresh limestone of the same band (H). The analyses 



gave : — 



° Fresh Limestone. " Floater." 



Gangue (mostly quartz) . . 5 "50 27 "09 



♦Phosphoric acid . . . . 0'15 022 



Not determined . . . . 9435 72'69 



10000 10000 



♦Equivalent of Ca 3 (P0 4 ) 2 . . 033 048 



These analyses prove, then, (1) that the limestone H con- 

 tains when fresh a small amount of phosphoric acid dissemi- 

 nated through its mass ; (2) that the ordinary process of wea- 

 thering, which carries away the calcium-carbonate in solution, 

 does not carry away the calcium-phosphate to an equal extent, 

 so that the latter tends to concentrate in the residue. 



The " Gut " at Millburn. — Brown and green sands and clays 

 fill the hollow between two pinnacles, and protect the lime- 

 stone surface from the atmosphere, but not from percolating 

 waters. In the deepest central " gut " the limestone is found 

 to have a thin veneer, about 0'75 in. thick, of a pulverulent 

 weathered limestone (C^). Outside this veneer comes 6 in. of 

 a green glauconitic and phosphatic sand (C 2 ), the whole of this 

 layer being laminated with fine streaks of not yet completely 

 weathered limestone, arranged rudely parallel to the present 

 limestone surface. Outside C 2 is found a varying thickness of 

 yellow-green very sandy clays (C 3 ), laminated parallel to the 

 surface of the limestone, the laminae being from 0'06 in. to 

 - 25 in. apart, and composed of alternating green and yellow 

 bands. These clays line the limestone wherever the latter is 

 protected from the atmosphere — on pinnacles, in hollows, and 

 on the under-side of projecting ledges alike. A tough yellow 

 richly phosphatic clay (C 4 ) is found in the midst of the yellow- 

 green clays ; it is sometimes in bands, more often in irregular 

 patches and nodules. 



The following analyses will show the manner in which the 

 concentrating action has taken place. The limestone has been 

 deprived of its CaC0 3 ; the quartz, glauconite, and to a great 

 extent the lime-phosphate, being insoluble, have been left be- 

 hind and concentrated to form C x and then C 2 . Then the 

 C 2 has been separated into two parts, the lime-phosphate tend- 

 ing to segregate into the clayey nodules C 4 , surrounded by 

 yellow-green clayey sand C 3 . This differential action is due 

 to water, which has acted by dissolving and then reprecipitat- 

 ing some of the lime-phosphate. 



