CLASSIFICATION OF THE ROCKS. Ill 



definite occurrences of the mineral talc. The thin, lustrous films of 

 hydrous mica give them, however, a very talcose appearance in the 

 field, and this character has enabled Messrs. King and Foote to 

 trace them north-eastwards as far as Munnikul hill (lat, 12° 8'; long, 

 78 47'), a distance of 46 miles. 1 



These schists are very variable in colour, including bands of 

 white, pink, grey, and green colour, giving them 



General characters. ° 



a very composite appearance ; some of the 

 bands are highly felspathic and often include " eyes M of uncrushed 

 pink felspar, quartz and mica, such as might arise from the partial 

 destruction of a coarse pegmatitic vein (11*922) in the original rock ; 

 others are simple hornblende schists, the result of deformation of 

 basic bands of igneous rock. 



Iron-ore beds. 



But the most conspicuous members of the group are the iron- 

 ore beds — Godamalai, which has been so graphically described by 

 King and Foote, 3 being the chief example within this area. The beds 

 forming this hill stretch westwards to a point about one mile north 

 of Karipatti, where they become poorer in quality and thin out 

 against the old gneiss; the well exposed section at this point also 

 shows the perfect interlamination of the iron-ore beds with the other 

 schists included in this group. 



The rocks of the iron-ore beds aire composed of quartz and a 

 pale-green amphibole (grunerite) with a mixture 



Mineral composition. 



of magnetite and hematite. Compared with the 

 thicker masses in Godamalai, the western extension is poor in iron- 

 ore, which forms about one-third only of the bulk of the rock 

 (No. 11*924). The quartz is quite clear and colourless, occurring as 

 small granules with sharp extinctions and in larger crystals with 



1 King and Foote, Op. cit., p. 270. 

 1 Op. cit., pp. 281—284. 



( 9 J 



