THE 15RIST0L COALFIELD. 



20 



Both beds give practically the same amount of silica. Silicate of 

 iron is absent, the whole of the iron existing as an oxide or carbonate. 

 The greater portion of the alumina is combined as a silicate, and a 

 portion of the lime also. The colour of the stone is grey, and it is full 

 of black specks of carbon. The exact thickness of the deposit I am 

 unable to give, but it will probably be about forty or fifty feet. 



The next deposit of rock to which I desire to direct attention is 

 that of the Doxall grit, which, however, is only about twelve feet thick. 



The name " Doxall " is derived from a seam of coal of that name 

 upon which the grit rests. In the great majority of cases, indeed 

 almost always, seams of coal are followed for a few feet by beds of 

 shale and other semi-argillaceous beds, known in the mining districts 

 of tie south-west of England as '-Dims." In the present case 

 these are absent, the grit resting on the coal. I wish, however, to 

 draw special attention to the difference in the composition of that 

 close over the coal and that which is not. 



ANALYSIS OF THE DOXALL GRIT NO. 1. STONE NOT CLOSE OVER COAL. 



NO. 2. — STONE CLOSE OVER COAL. 



Soluble in Acid. Insoluble in Vci':. 



Silica 



Alumina 



Iron 



Lime 



Carbon 



Carbonic Acid 

 Magnesia .... 

 Manganese .. 

 Phosphorus . . 



Sulphur 



Water 



2-2 

 5 53 

 ■70 



Total. 



75-: 5 



856 



5 53 



•70 



805 



•33 



Trace. 



•26 



Not estimated. 



•74 



■60 



A comparison of these analyses shows that in the case of the stone 

 which rests upon the coal the proportion of alumina has increased, in 

 other words, it has become more argillaceous. Also, we find 

 manganese, phosphorus, and sulphur present. Having called attention 

 to this change in the chemical composition of the stone, I will pass on 

 to review the other deposits of grit, and revert to it again presently. 

 (To be continued.) 



