238 Outlines of Geology. 



lime ; siliceous lime, or dunstone ; and towards its lower parts 

 are the beds of black marble, which receives a good polish, and is 

 manufactured into various ornamental articles. The lowest 

 limestone stratum is that which forms the peak forest, the downs 

 of Buxton and the Weaver-hills, and in it are several remarkable 

 caverns, such as the Devil's -hole, Elden and Poole's-hole, and many 

 others. Here also we find at Castleton those curious nodules and 

 masses of fluor-spar, celebrated for the manufacture of vases, and 

 a variety of other beautiful ornamental articles, as also that very 

 singular mineral product called elastic bitumen ; and the caverns 

 abound in splendid stalactites and stalagmites, whilst their waters 

 acquire a petrifying power from carbonate of lime. 



The toadstone of Derbyshire is sometimes considered as regu- 

 larly stratified between the limestone beds, but upon this subject 

 considerable doubts may be entertained, and at all events the beds, 

 if such they be, are liable to many extraordinary irregularities 

 which will furnish matter for future consideration. The toad- 

 stone never contains shells, nor organic remains, which are so 

 abundant in the alternating limestone. Nodules of chalcedony 

 and zeolite ; globules of calcareous spar, and some other substances, 

 are not uncommon in it, and however unsatisfactory or inadequate 

 our theories are, in respect to this extraordinary substance, it 

 must by all be allowed to bear the marks and characters of a 

 distinct formation. 



In the cave at Castleton it forms a large, irregularly- shaped 

 column, which has all the appearance of common basalt, and oc- 

 casionally it acquires a columnar feature ; so that for this, and 

 various other reasons, I shall transfer the history of the Derby 

 toadstone to that of those irregularly-occurring rocks that some- 

 times are found in primitive, and sometimes in secondary strata. 



The veins in the limestone of Derbyshire contain lead, manga- 

 nese, copper, and also ores of zinc and iron. The proper repository 

 of the lead appears to be the limestone, though it also occurs in some 

 other strata, and rarely in the toadstone, in which it is always in 

 small quantities, and merely in strings, or very imperfect veins. 



Near Bristol, the limestone hills rise from below the red sand- 



