366 MB. H. H. ARNOLD-BEMROSE ON [Aug. I9°4> 



have straight extinction, but others extinguish up to an angle of 

 18°. (See PL XXXI, fig. 4.) 



On a visit to the quarry this year at Easter, I was told by the 

 foreman that some silver-sand had been found in a small fissure 

 or joint in the limestone. I examined the fissure, and obtained some 

 sand of a reddish-brown colour. After it had been washed it 

 was examined under the microscope, and found to consist mainly 

 of quartz-grains, the majority of which were well-rounded, with a 

 few flakes of white mica. 



(2) The Quartzose Limestone. 



The rock (1232) in contact with the last-described dyke consists 

 of crystalline calcite, containing a lar»e quantity of quartz in isolated 

 crystals and in granular aggregates. The quartz sometimes encloses 

 calcite. Two feet below No. 1232, the limestone (1233), which is in 

 contact with the same dyke, contains traces of organisms and many 

 bipyramidal crystals of quartz. 



A thin slice (1234) of the partly-dolomitized limestone was 

 examined. It consists of remarkably well-defined and often isolated 

 rhombohedra of dolomite, in a matrix of finely-crystalline calcite. 

 The quartz occurs in granular aggregates and in isolated crystals. 

 A small piece of the rock was dissolved in strong hydrochloric acid, 

 and the residue was found to consist of bipyramidal quartz-crystals 

 and a small quantity of brown material. 



Quartz-crystals were also found in other parts of the limestone. 

 The thin grey limestones at the south-western end of the quarry 

 are traversed by small calcite- and quartz-veins. 



The thin slice (1236) consists of a limestone containing fora- 

 minifera, Caleisphcera, and a few isolated crystals of quartz. The 

 slice is traversed by a small vein of quartz in a fine mosaic, similar 

 to the quartz-strings or veins in the limestone near Bonsall. 1 



These quartzose limestones are similar to those described by me 

 in a paper read before this Society in the year 1898. 2 



o 



(3) The Calcite. 



Between the thin beds of limestone at the south-western end of 

 the quarry and the 4-inch quartzite-dyke described above, is a 

 vein of calcite several feet thick. It appears in part to be bedded 

 like limestone, and shows horizontal slickenside-faces between the 

 joints. It consists (1237) of crystalline calcite, with polysynthetic 

 twinning well developed. Some portions are red, and are similar to 

 the ' Hartington Red,' formerly obtained near Hartington between 

 Ashbourne and Buxton, and polished as marble. Other portions 

 are white. The red coloration is due to oxide of iron, which occurs 

 in small dendritiform patches. 



1 Quart, Journ. Geol. Soc. vol. liv (1898) pp. 173 & 174, thin slice Js T o. 431. 



2 Bid. pp. 169 to 182. 



