gneissic rocks : quartz reefs. 67 



3. Quartz reefs and veins. 

 Not many examples of this form of rock were met with^ but several 

 of them were of considerable size and importance. They consist 

 mostly of pure white quartz, showing, in some cases, an obscure, quasi- 

 brecciated structure, which is most conspicuous where the apparently 

 included fragments are surrounded by a pale green chloritic staining. 

 This staining is, generally, only locally seen. It may be well developed 

 in a small part of a reef and not at all seen in other parts. A good 

 example of such a quasi-brecciated reef is that running north-westward 

 from near Nykal on the right bank of the Bhima, and forming a ridge 

 whose northern end is locally called the Murubukul. In a small quartz 

 reef, a mile and a half north-west of Bhanur (Bunnoor) in the Raichur 

 Doab, the chloritic surrounding of the quasi-breccia fragments amounts 

 to a distinct film. 



The large quartz reef at Bahadurdinni, six miles east of Kautala 

 (Civital), is also a good specimen of the quasi-brecciated quartz. 



Some of the reefs present a laminated structure, closely resembling 

 true bedding. A remarkable instance of this may be seen in the large 

 reef at Marudgi, on the left bank of the northern branch of the Krishna^ 

 3 miles north of the junction of the Ghatprabha with the southern 

 branch. The reef here appears to have a dip of from 70° to 85° south- 

 by-east, and the lamination is very distinct in the middle part of its 

 course, owing to the presence of thin films of haematite between many 

 of the laminse. 



Although, generally, these reefs consist of pure quartz only, with but 

 few important enclosures, there are some cases in which they show a large 

 amount of some accessory mineral, specially of the specular variety of 

 red haematite. The most noteworthy example of this occurs in the 

 double reef at Yerramarsu (Yerrumursoo), 2 miles north of Siriwar 

 (Seerewar), a large village on the Baichur — Ling Sugur road, and about 

 21 miles west of the former place. The ore occurs in numerous little 



( 67 ) 



