48 NOTES ON CRICH HILL. 



four inches thick. It is coloured red with oxide of iron, and 

 contains small crystals of selenite. In several places, the gate 

 traverses faulty rock, which has to be kept up by building an arch 

 or roof of stone or timber. About four yards of faulty rock 

 obscures the junction between the limestone and the toadstone 

 below it. The word toadstone is a very vague one as used by 

 miners. It occurs black or dark green when fresh, with larger 

 or smaller crystals glistening in it. At the top or bottom of a 

 bed it is often vesicular, i.e., contains steam holes like those 

 in slag, or in pumice stone, due to the escape of gas when the 

 rock flowed in a molten stream as lava. These holes are 

 often filled with carbonate of lime, by the infiltration of water, 

 and the rock is then said to be amygdaloidal. Under the 

 action of air and water, toadstone becomes decomposed, and 

 altered to a greenish-coloured rock, and even to a sort of clay, 

 so that miners have sometimes taken a bed of clay to be 

 altered toadstone. 



In this mine they call the dark-coloured rock " Blackstone," and 

 the decomposed part of the same Toadstone. After passing the 

 faulty rock which obscured the junction, we first came to the dark 

 rock, which in its upper part contained a number of amygdaloids 

 of calcite, giving it a spotted appearance. Numerous veins 

 of calcite cross it in all directions, and it is difficult to get a 

 large piece without a vein in it. This passes downwards into a 

 hard black rock, and this again into a softer, greenish-coloured 

 rock, which lies on the limestone, and is only separated from it 

 by a layer of clay, several inches thick, similar to the clay above 

 menticmed, and like it containing crystals of selenite. After pas- 

 sing through more beds of limestone, we came to the twenty fathom 

 clay, the top of which forms the floor of the "gate" for some 

 distance. This clay also contains crystals of selenite, and is the 

 lowest bed we touched. Proceeding, we soon noticed that the 

 dip had changed, and was nearly east instead of west, and that we 

 had therefore passed the centre of the dome. After some time 

 we arrived again at the same bed of toadstone on the other side 

 of the hill. At the top of the gate the rock appeared very much 



