178 MB. H. H. AENOLD-BEMEOSE ON A QUAETZ-EOCK [May 1 898, 



between them. It might be described as an intimate mixture of 

 granitic and microgranulitic (Michel-Levy) quartz. 



No. 579. The grains vary much in size, and many of the larger 

 among them are elongated. Zonal inclusions are frequent, and are 

 in several cases arranged in the form of a regular hexagon or a section 

 of the prism with pyramidal terminations, though the grain itself 

 possesses no crystalline outline. In the former case the grain 

 remains extinct between crossed nicols, in the latter it extinguishes 

 with the axis of the prism. These facts show that the grains are 

 not a secondary growth around detrital quartz, but that they 

 originally had a crystalline outline, and then interfered with each 

 other's growth : that they were in fact idiomorphic, and then became 

 allotriomorphic. The structure is a combination of the granitic (with 

 a tendency for some grains to become elongated in the direction of 

 the axis of the prism) and the microgranulitic. 



(j) Brock Tor (6-inch Map 9, S.E.), immediately north 



of Moss Rake. 



This rock is similar to that of Bathamgate, both in the field and 

 .under the microscope. 



(k) Oxlow Eake (6-incli Map 9, S.E.). 



The few isolated blocks near this Rake are quartz-rock of the Top 

 Lift type. 



(Z) Doveholes (6-incli Map 15, N.W.). Old Quarry near 



Bull Ring. 



I have not been successful in finding any quartz-rock in this 

 -quarry, but a small quantity of the limestone in one place contains 

 numerous quartz- crystals. They appear to be local, and the 

 quartzose limestone shades off quickly into the ordinary white 

 limestone. Two thin sections were examined. 



No. 443, sp. gr. 2-65, is a limestone with few foraminifera and a 

 large numb9r of quartz-crystals. The quartz often contains calcite 

 in zones, but more often in irregular patches. The two are 

 sometimes blended, as if the quartz were in the act of crystallizing 

 round a portion of the adjacent calcite. Where the quartz is 

 surrounded by fibrous calcite, it often contains inclusions of the 

 latter mineral arranged roughly parallel to the fibres. 



No. 444 consists of calcite, with possibly a few traces of fora- 

 minifera, and many quartz-crystals. The quartz often contains 

 calcite. The residue consists of quartz-crystals, varying in size 

 from -35 x '10 mm. to -10 X "025 mm. 



It is interesting to contrast the microscopic structure of the 

 foregoing rocks with the chert and the ' siliceous limestone ' near 



