208 



BROWELL AND KIRKBY ON MAGNESIAN LIMESTONE 



twenty per cent. Five out of the six also contain carbonate of 

 magnesia. "We are rather inclined to ascribe the presence of 

 both to natural deposition along with the siliceous (and other) 

 materials, though they may be due to infiltration from the over- 

 lying limestone. But we have seen a similar Permian rock at 

 Knaresbro', in Yorkshire, so highly calcareous, (passing grad- 

 ually on the one hand into pure magnesian limestone, and on 

 the other into a true sandstone,) as to have been mistaken and 

 described for a limestone. The lime in this rock must evidently 

 have been deposited. 



The chief and almost only economic value of this deposit con- 

 sists in the storage it affords for a large supply of good water. 

 Its absorbent properties are well known, both from the money it 

 has lost, as well as the money it has gained enterprising specu- 

 lators for coal or water, as the case may be. "We have made a 

 few experiments on the quantity of water which the sandstone 

 is capable of holding, the results of five of which are given in 

 the following table : — 



TABLE IT, 



ILLUSTRATIVE OF THE ABSORBENT PROPERTIES OF THE LOWER 

 RED SANDSTONE. 



No. 



1 



2 



3 

 4 

 5 



LOCALITY. 



Weight of a cub. ft. 

 of Sandstone, dry. 



Weight of a cub. ft. 

 of Sandstone, wet. 



Water absorbed by a 

 cub. ft. of Sandstone. 



Claxheugh . . 

 Fulwell .... 



lbs. 

 108-0 



155'37 



125-3 



121 93 



118-75 



lbs. 

 120-5 



161-50 



135-56 



134-12 



131-25 



lbs. 

 12-5 



6-13 



10-26 



12-19 



12-50 









The third column represents the weight of the sandstone stove- 

 dried ; the fourth column the weight of it thoroughly saturated. 



Some idea of the enormous supply of water that may be (and 

 evidently is) thus stored in this rock may be obtained by calculat- 

 ing the quantity absorbed by a square mile of it (say fifty feet 

 thick, at the rate of ten pounds or a gallon per cubic foot), which 

 gives 1,393,920,000 gallons. Fifty such miles, which may be 



