Andkew. — On the Clarendon Phosphate-dejwsits. 477 



The C 1 column does not tally exactly with the results from the 

 other columns, and this is probably due to errors in the chemical 

 analysis. It must be remembered also that any errors that do 

 occur in the analysis are almost doubled in the case of C 1? while 

 they are diminished in the case of the others, roughly in the pro- 

 portion of 3 to 1 and 6 to 1 respectively. Noticing the other 

 columns only, we see that the iron and alumina, like the silica, 

 are not removed by the weathering process, 5*35 resulting from 

 5'36. The amount of moisture (H 2 0) is of no importance in this 

 inquiry, though apparently it also does not change much. P 2 5 , 

 however, has been abstracted, 1/33 resulting from l - 72. This dif- 

 ference is too great to be merely due to error in analysis. It is 

 clear, then, that phosphoric acid has been dissolved out from 

 the clays ; it joins the downward circulation, and is redeposited 

 where conditions are favourable. 



Stages of Process. — The amount of action that has taken 

 place in this gut at Millburn is small, but the full sequence of 

 operations is clearly seen. At Wilson's quarry the process is 

 more advanced, and has resulted in the formation of a large 

 quantity of phosphatic clays, which are now being cemented to- 

 gether by the redeposition of the phosphoric acid as lime-phos- 

 phate in the cracks which traverse the clay. The process has 

 reached its final stage at the Round Hill quarry, where all the 

 calcium-carbonate of the limestone has been dissolved away, its 

 place being now occupied by a mass of rock-phosphate. The final 

 stage has likewise been reached on the right-hand side of the 

 limestone quarry at Millburn, where now two boulders of hard 

 rock-phosphate, in the middle of the brown sands, rest on the 

 chemically eroded surface of the limestone. 



Objections. — The objections which may be advanced against 

 this theory are, I think, the following : — 



1. That the process outlined cannot account for large quan- 

 tities of rock-phosphate such as are found at Round Hill. To 

 explain such a large occurrence it is only necessary to suppose 

 that the original limestone at that point contained a very great 

 number of organic remains, such as bones, &c, and this suppo- 

 sition is upheld by the occurrence of numerous bone-fragments 

 among the phosphate at Round Hill. 



2. That the rock-phosphate ought to be always accompanied 

 by brown sands or sandstone. As a matter of fact it usually is, 

 though it is not necessary that it should be so ; the original lime- 

 stone now eroded away may at one place have been rich in phos- 

 phate, poor in silica : this would produce a rock-phosphate with 

 very little sandstone about. Conversely, the original limestone 

 at another place may have been rich in silica, poor in or destitute 



