"Vol. 54.] quaetz-kocb: in cakboniferotts limestone. 169 



.2. On a QiJAETz-RocK in the Carboniferous Limestone of Derby- 

 shire. By H. H. Arnold-Eemrose, Esq., M.A., F.G.S. (Read 



February 2nd, 1898.) 



[Plates XI & XII.] 



Contents. p^^^ 



I. Introduction 169 



11. The Southern Area 170 



III. The ]!^orthern Area 176 



IV. The Quartz-rock is a Limestone which has been 



replaced by Crystalline Quart/, 179 



V. The Origin of the Quartz 181 



I. Introduction. 



The object of this paper is to give a detailed description of a rock 

 consisting essentially of quartz, which occurs in the Mountain Lime- 

 stone of Derbyshire. It is not a quartzite in the ordinary meaning 

 of the word — that is, a sandstone indurated by the deposit of inter- 

 stitial quartz or by the recrystallization of the detrital grains into a 

 dear mosaic, though sometimes a specimen may be found simulating 

 the latter structure. It belongs rather to the second division of 

 quartzite suggested by Mr. Rutley,^ namely, that of an infiltration 

 or metasomatic quartzite ; in other words, it is a silicified limestone. 

 The term ' quartz-rock ' will, therefore, be applied to it in this 

 paper. 



Often associated with the quartz-rock is a quartzose limestone. 

 This is a fossiliferous limestone containing a large number of quartz- 

 crystals, which may be easily seen with a lens when the rock is wet. 



I first noticed the quartz-rock when commencing my study of the 

 Toadstone some years ago. Near the village of Bonsall, the foot- 

 path from Ember Lane to Pounder Lane passes a bold outcrop of 

 hard rock, locally known as the ' Top Lift.' A thin section from it 

 was prepared, and on examination was found to consist of quartz- 

 grains. Until about 2 years ago it lay in my cabinet. Since 1894 

 I have been engaged during my spare time in re-mapping the Toad- 

 stone and in trying to differentiate successive horizons in the lime- 

 ,stone in order to decipher, if possible, the history of the volcanic 

 eruptions in Derbyshire. In doing this I have met with the quartz- 

 rock in various localities. Its presence in the limestone rendered 

 the task of tracing the horizons in that rock more difficult. It was 

 therefore thought necessary to find its relations to the limestone. 

 With this object in view, I revisited every part of the limestone- 

 region where I remembered that I had seen any similar rock, and 

 examined a large number of thin sections. Though every outcrop 

 may not have been seen, sufficient has been done to prove that the 



1 ' On the Origin of ceL'tain Novaculites and Quartzites,' Quart. Journ. Geol. 

 ^00. vol. 1 (1894) p. 380. 



