10 HAYDEN AND HATCH; GOLD-FIELDS OF WAINAD. 



(i) Gneiss. 



The rocks which fall under this head are typically biotite gneisses 

 and show but slight variation from a common type ; they form the 

 greater part of the " country " rock in south-east Waina'd, and 

 extend over almost the whole area from Nadugani to Cheramb^di. 

 They are always well foliated, the strike of foliation being almost 

 invariably from east-north-east to west-south-west. Intrusions of 

 charnockite and of a basic hornblendic rock are not uncommon. 



The chief constituents of the gneiss are quartz, felspar, biotite 

 garnet (PI. 2, fig. 1). These are almost 



Constituent minerals. . 



invariably present, while a few other minerals, 



viz., zoisite, epidote, chlorite, muscovite, rutile, iron ores {magnetite, 



pyrite, ilmenite), sphene and calcite are accessory, many of these 



being of secondary origin. Actinolite is found in the more basic 



bands occurring in the gneiss, and is particularly common at its 



junctions with the charnockites and with certain hornblendic rocks 



(epidiorite) found at the Phoenix mine on the southern flank of 



Hadiabetta and on Hamsluck estate, near Devala. 



The quarts, which occurs in considerable quantity, is usually 



clear and granular, but occasionally contains 

 Quartz. 



numerous hair-like inclusions, too small to be 



determined definitely. 



The felspar includes both monoclinic and triclinic varieties : the 



latter represented by small crystals of oligoclase 

 Felspar. 



albite, and a form approaching labradorite ; they 



are at times fairly fresh but are frequently decomposed with the 



formation of epidote and muscovite, which in some instances 



completely replace the original felspar. 



The biotite is of the common brown variety 

 Biotite. ,.,,., 



and is seldom, if ever, absent. 



Garnet has been found in almost every specimen examined and 



is a characteristic constituent of the gneiss : the 

 Garnet. 



crystals are usually cracked and broken and 

 ( 10 ) 



