SUMMARY. H3 



Madras Presidency. Alhough the Nilgiri mass, for in- 

 stance, covers an area of some 700 square miles with an 

 average elevation of over 7,000 feet, it is composed almost 

 wholly of the charnockite series, which retain their charac- 

 teristic features throughout and are sharply marked off 

 from the gneisses and schists of the surrounding plains 

 below. No such thickness could be paralleled by a homo- 

 geneous formation of any sedimentary rock. 



(2) Internally the large charnockite masses show the characteris- 



tic structural variations of common igneous massifs — basic, 

 fine-grained, segregative schlieren (autoliths) y coarse-grain- 

 ed, acid, contemporaneous veins, and primary eruptive 

 breccia — features indicative of the free internal molecular 

 translations which are presumably characteristic of, and 

 restricted to, rocks which have passed through a molten 

 condition. The frequent directional arrangement of the 

 constituents presents no feature at variance with the simi- 

 lar phenomenon seen in igneous masses, and the imperfect 

 banding is no more than would follow the deformation of 

 an imperfectly segregated (schlierig) magma. 



(3) Apophyses have been observed protruding from a large 



mass into crushed, altered and older biotite-gneiss, whilst 

 well-defined dykes — often garnetiferous — have been found 

 with fine-grained, basic selvages, due presumably to chil- 

 ling at their contacts with the older gneisses. 



(4) Although the charnockite series are too old to be found in 



contact with any but rocks already crystalline, fairly well- 

 defined contact phenomena have been recognised near 

 their junctions with quartzites, and, less certainly, in the 

 neighbourhood of limestones. 



(5) Ellipsoidal bodies composed principally of pink microper- 



thite, with corundum, sillimanite, rutile, hercynite and 

 Hiotite, possessing characters strange to the normal 



( "5 ) 



