On the Microscopical Structure of the Carboniferous Dolerites and Tuffs of Derbyshire

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Abstract
I have, in the first place, to thank Mr. Teall for the suggestion that I should work out the Derbyshire loadstone by the modern petrographical methods. I am not aware that the results of any detailed examination of the rocks have been published. Mr. S. Allport described five specimens from Matlock Bath and one from Bonsall. I have examined his specimens and find them to be much more altered than the rock is in many places. The Cave Dale rock has been described and the Tideswell Dale rock has been both described and figured by Mr. Teall. The first person who wrote about the rock and called attention to its igneous nature was, I believe, Whitehurst, the clockmaker of Derby. He considered it to be intrusive, but it is now generally admitted to be contemporaneous with the Carboniferous Limestone. The rock occupied the attention of many writers previous to the use of the microscope in petrography, and various opinions have been expressed and statements made about the number of beds and the non-occurrence of lead ore in it. It should be pointed out, that owing o the vague use of the word ‘Toadstone’ is derived either from the supposed resemblance of the amygdaloidal varieties to the back of a toad, or the word is a corruption of the German ‘Todtstein’ (Deadstone) and so called because it was supposed that no lead ore wasfound in it. Though a mineral-vein is often cut off by the Toadstone, there are some undoubted cases in

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