604 ME. H. H. ARNOLD-BEMROSE ON THE MICROSCOPICAL [Nov. 1 894, 



Tbe rock occupied the attention of many writers previous to the use 

 of the microscope iu 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 to the vague use of the word ' Toadstone ' by miners, their 

 statements as to the number of beds must be accepted with reserve. 

 It is now impossible to verify such statements, because most of the 

 mines are closed. The local name ' Toadstone ' is derived either 

 from the supposed resemblance of the amygdaloidal varieties to the 

 back of a toad, 1 or the word is a corruption of the German 

 ' Todtstein ' (Deadstone) and so called because it was supposed that 

 no lead ore was found in it. 2 



Though a mineral-vein is often cut off by the Toadstone, there 

 are some undoubted cases in which the lead-ore has been worked 

 in that rock. About two years ago I visited the Wakebridge Mine 

 near Crich, and examined the rock in which the ore was being 

 worked. It was a much decomposed olivine-dolerite. 3 



All the outcrops except two occur in the Mountain Limestone. 

 Near Kniveton are two outcrops of igneous rock among the Yore- 

 dale Beds (nos. 57-58). According to the Survey memoir they cut 

 across the shale and limestone, so that their boundaries are faults 

 or the Toadstone here is intrusive. Sir A. Ramsay considered the 

 latter view the safer. 4 The rocks in the neighbourhood are so con- 

 torted that it is difficult to say how far these views are correct. I 

 have not been able yet to spend enough time at the locality to 

 come to any opinion on the matter. 



The spheroidal structure is well developed in many places, notably 

 in Tideswell Dale, Priestcliffe Lane, New Bridge, and a rude 

 columnar structure occurs in Cave Dale, near Castleton, and in 

 Tideswell Dale. 



Where exposures are seen which show its relation to the lime- 

 stones above and below it, there is no doubt about the age of the 

 Toadstone. The Geol. Surv. Memoir, p. 123, gives reasons for the 

 belief that it is contemporaneous with the limestones. According 

 to the memoir, the Toadstone is never seen to cut across beds of 

 limestone, and although clay beds below it have been in some cases 

 baked and caused to assume a columnar structure, as in Tideswell 

 Dale, 5 those resting on the Toadstone show no trace of alteration. 

 The abundance of the amygdaloids in the upper part of a sheet, the 

 bedded ash near Ashover, and the bedded agglomerate at Blopton 

 are cited as evidence of its being interstratified with the limestone. 



1 ' Essai sur l'Oryctograpbie clu Derbyshire, par M. Ferber,' quoted by Faujas 

 de St. Fond in 1799, ' Travels in England, Scotland, etc.,' vol. ii. pp. 284 et 

 scqq.; also J. Farey, ' General View of the Agriculture and Minerals of Derby- 

 shire,' vol. i. (1811) p. 277. 



2 Green, ' Physical Geology,' 1882, p. 554: 



3 ' Notes on Crich Hill,' Journ. Derbyshire Archasol. & Nat. Hist. Soc. vol. xvi. 

 (1894) pp. 44-51. 



4 Mem. Geol. Surv. North Derbyshire, 1887, pp. 86-87. 



5 ' On an Altered Clay-bed and Section in Tideswell Dale,' by the Rev. J. M. 

 Mello, Quart. Journ. Geol. Soc. vol. xxvi. (1870) p. 701 ; also E. Wilson, Geol. 

 Mag. 1870, p. 520. 



