Vol. 50.] CARBONIFEROUS DOLERITES AND TUFFS. 603 



39. On the Microscopical Structure of the Carboniferous Dolerites 

 and Tuffs of Derbyshire. By H. H. Arnold-Bemrose, Esq., 

 M.A., F.G.S. (Read June 6th, 1894.) 



[Plates XXIV. & XXV.] 



Contents. 



Page 



Introduction 603 



Table of Outcrops and Mine-heaps 606 



Part I.— The Lavas 611 



1. Olivine. 



2. Potluck Pseudomorphs after Olivine. 



3. Peak Forest Pseudomorphs after Olivine. 



4. Rhombic Pyroxene. 



5. Augite. 



6. Felspar. 



7. Structure of the Lavas. 



Part II.— The Fragm ental Eocks or Tuffs 625 



Castleton, Outcrop 1. 

 Brook Bottom, Outcrop 7. 

 Litton, Outcrop 8. 

 Dove Holes, Outcrop 12. 

 Monk's Dale, Outcrop 16. 

 Bavensdale Cottage, Outcrop 18. 

 Miller's Dale Station, Outcrop 19. 

 Cracknowl House, Outcrop 34. 

 Ember Lane, Outcrop 39. 

 Grange Mill, Outcrop 46. 

 Hopton, Outcrop 53. 

 Kniveton, Outcrop 54. 

 Kniveton, Outcrop 56. 

 Ashover, Outcrop 59. 



I have, in the first place, to thank Mr. Teall for the suggestion that 

 I should work out the Derbyshire Toadstone by the modern petro- 

 graphical 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. 1 

 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. 2 



The first person who wrote about the rock and called attention 

 to its igneous nature was, I believe, Whitehurst, the clockmaker of 

 Derby. 3 He considered it to be intrusive, but it is now generally 

 admitted to be contemporaneous with the Carboniferous Limestone. 



1 ' On the Microscopic Structure and Composition of British Carboniferous 

 Dolerites,' Quart. Journ. Geol. Sol. vol. xxx. (1874) pp. 529-567. 



2 ' British Petrography,' pp. 209, 210, and pi. ix, 



3 'An Inquiry into the Original State and Formation of the Earth,' by John 

 Whitehurst, 1778, pp. 149 et seqq. 



