402 



PEOCEEDIDfGS OF THE aEOLOGICAL SOCIETY. 



[Dec. 1, 



the persistent inclination of superposed strata (in the last case to the 

 E.N.E.) induces Mr. Dick as well as myself to assign very consider- 

 able dimensions to the deposit. 



The manager of Mr. Traill's large quarries at Castle Hill (Mr. 

 McBeath) defines sixteen different beds, nearly all of which, to the 

 ordinary eye, present a great sameness of structure. Seeing the 

 indestructible character of this hard pavement-stone, which resists 

 the weather, even when set on edge to form fences, I suggested, 

 when on the spot, that their great tenacity and resistance to the 

 atmosphere were in all probability due to the fine admixture of 

 silica and alumina, in a finely pulverized condition, with certain 

 proportions of carbonate of lime and bitumen (the latter chiefly 

 obtained from the numerous fossil fishes of the deposit), with traces 

 of iron. The analysis of Dr. Hofmann, to whom I submitted four 

 varieties of the flagstone of Castle Hill, taken from the base, middle, 

 and summit of the Castle Hill quarries, has confirmed the view as 

 given in the Table of the accompanying footnote*. Where the 







-Si- 



Table. 











Mineral analysed. 



Silica and 

 Silicates, 

 insoluble 

 inHCl. 



Oxide of 

 Iron and 

 Alumina. 



Carbo- 

 nate of 

 Lime. 



Organic 

 matter. 



Water, 

 loss at 

 lOO^C. 



Salts of 

 Magnesia, 



the Al- 

 kalies, &c. 



Total. 



No. 16. Top flag. . 

 No. 7. Middle flag 

 Bituminous Shale. 

 No. 1. Bottom flag 



68-40 

 69-45 

 69-96 

 61-39 



10-21 

 11-50 



8-15 



4-87 



10-93 

 10-66 



7-72 

 21-91 



3.88 



5-79 



10-73 



3-40 



0-42 

 0-40 

 0-53 

 0-20 



6-16 

 2-20 

 2-91 



8-23 



100-00 

 10000 

 100-00 

 100-00 



In analysing a portion of the bituminous schists from the property of the 

 Earl of Caithness (near Barrogill Castle), Dr. Hofmann reported to me as fol- 

 lows: — "When submitted to the action of heat, this substance evolves a consi- 

 derable amount of gas, and likewise of oily matter containing a certain propor- 

 tion of ammonia. The residue which remains behind is a greyish mass, con- 

 sisting essentially of silicate of alumina (clay) mixed with a certain quantity of 

 sesquioxide of iron and of sulphate of lime. A very minute proportion of 

 phosphoric acid was Hkewise found to be present. The loss which the mineral 

 undergoes on heating was found in two consecutive experiments to be 30-21 and 

 30-02 ; so that the mineral may be said to contain, in round numbers, 



" Fixed matter (mineral) 70 per cent. ; volatUe matter (organic) 30 per cent. 



" In determining the amount of gas furnished by the distillation of the 

 mineral, a portion of it was heated in an iron tube, in order to imitate, as nearly 

 as possible, the circumstances of an operation on a large scale. In two consecu- 

 tive experiments which were performed in this manner, 100 grammes furnished 

 in one case 7690 cub. centim., and in another 7430 cub. centim. 



" Assuming then 100 grammes of the mineral to yield, on an average, 7500 

 cubic centimetres of gas, a ton of the material would furnish 2690 cubic feet. 

 The ordinary varieties of coal used in gas-making yield from 8000 to 10,000 

 cubic feet of gas per ton. The gas obtained from the mineral is very luminous ; 

 it is nearly entirely free from sulphur, and it is on this account very readily 

 purified. The residue left in the retort after the expulsion of the gas retains but 

 a small amoxmt of carbon, viz. 8-5 per cent. ; this residue has therefore but little 

 value as coke. 



'• The mineral in question is in no way related to ozokerite, as has been sug- 

 gested. From that substance it may be at once distinguished by its infusibility 

 (ozokerite fuses at 80° C.=:176° Fahr.), and by its entire insolubility in alcohol 

 and ether, in which solvents ozokerite, although with difficulty, dissolves." 



