264 EXPERIMENTS WITH SHALES, 



6. Suggestions for experiments with bituminous and oilier 

 shales, burned and unburned. 



In connexion with surface clays, I would draw the attention 

 of my readers to bituminous and sulphury shales, which are not 

 unfrequently used with advantage in practical agriculture. A 

 shale is a more or less indurated clay, which splits into thin 

 shivery layers, and is called bituminous or sulphury according 

 as it yields the one or the other on the application of heat. The 

 bitumen is derived chiefly from vegetable matter, and the sul- 

 phur from iron pyrites with which the clay is impregnated. 

 Both in the burned and unburned states, such shales have been 

 applied to the land. 



1. Unburned shale. Common coal shale, neither sensibly 

 bituminous nor sulphury in a marked degree, has been used with 

 advantage in improving and consolidating loose sands in the 

 neighbourhood of coal mines from which the shale had been 

 extracted. This is only a variety of claying or gaulting, and 

 the mode in which it produces improvement is readily under- 

 stood. 



Subordinate to the Oxford clay, beds of bituminous shale 

 occur in some localities which are found to benefit ordinary land. 

 In the Journal of the Boyal Agricultural Society of England* 

 Mr Gowen has published the analysis of a shale of this kind 

 which contained about 20 per cent of combustible matter, nearly 

 as much carbonate of lime, and probably some sulphur, which is 

 not stated. It occurs near Chippenham in Wilts, crumbles by 

 the action of the frost, and forms a valuable top-dressing for 

 grass land. Our coal shales rarely contain so much lime as this 

 of Mr Go wen's, which is subordinate to the calcareous Oxford 

 clay. Whatever might be the effect of its other ingredients, 

 it contained lime enough to act as a marl, and might on this 

 account alone be beneficial. Any other shales, however, 

 which are crumbled by a winter's frost, may be tried on light 

 and gravelly soils with the prospect of benefit. 



2. Burned shales. Sulphury shales, wherever they occur, 

 may be burned, as we burn clay, either alone, or, when they 



* IV. p. 277. 



