232 a popular sketch of the 



The Toadstone. 



The toadstone is a basaltic* rock which in its dark colour and its 

 sometimes spotted appearance is supposed to resemble the back of a 

 toad ; whence its name. It varies greatly in character and appear- 

 ance, being sometimes a hard compact basalt, perfectly black, and 

 homogeneous in its structure ; sometimes a light cellular stone of a 

 brown colour, the cells heinq: filled with crystals of zeolite, meso- 

 type, agates, or other minerals. Upon exposure to the weather 

 these substances sometimes decompose and fall out, when the toad- 

 stone assumes exactly the appearance of a scoriaceous lava. It is 

 never stratified, but is often jointed in all directions, and is some- 

 times laminated. It frequently has a tendency to decompose into 

 balls, but never assumes anything like a decided columnar structure. 

 The thickness of the toadstone varies from eighty to upwards of 

 three hundred feet.t Its upper and lower surface is almost invari- 

 ably covered by, or rests upon, several feet of a greenish yellow 

 clay, which frequently contains balls and lumps of toadstone, and 

 which is apparently the result of the decomposition of the bed. 

 That this is the case seems to be proved by the condition of the 

 limestone that rests upon it, which is frequently conformable to the 

 uneven surface of the toadstone clay. In the Wheal's Rake minej 

 in Lathkill Dale, the lower bed of a mass of Limestone is seen rest- 

 ing on a thick mass of toadstone clay, which passes downwards into 

 toadstone. The upper surface of this clay is very uneven, being all 

 knolls and hollows ; and from its soft nature it falls down in places 

 into the workings, and leaves exposed the under surface of the lime- 

 stone. This under surface is just as uneven as that of the clay, and 

 indeed exactly fitted on to it, containing hollows two or three feet 

 deep and the same distance across, out of which a mass of clay has 

 fallen, or protuberances fitting into hollows of the clay, and com- 



• Basalt or trap is one of that numerous class of rocks which are known to 

 be the product of heat, or to have cooled down to their present condition from 

 a state of fusion. 



f In the valley of Ashover, I was informed by Mr. Milnes, of Stubbing 

 Edge, that they had sunk in 1788, at the Townstead shaft. 375 feet in the 

 loadstone, and then bored thirty or forty feet without getting through it. 

 In other parts of the same valley, however, it is much thinner, being only 

 two hundred feet thick at a shaft about three hundred yards distant from the 

 former. 



X I am indebted to Mr. J. Barker, of Bakewell, for a sight of these mines, 

 and for much valuable information respecting them and the district in gene- 

 ral. 



