lS6 HOLLAND: CHARNOCKITE SERIES. 



• 

 serpentinization, although the dykes are converted into a yellow 



clay where they come to the surface. 



The south-eastern face of the Nilgiris is a steep, precipitous 

 South-eastern face of the scarp with an average direction of E.-N.-E. — 

 W.-S.-W., which is the direction also of foliation 

 in the hill. The rocks are much more definitely foliated near this face 

 than further towards the centre of the plateau, and the foliation is 

 accompanied by a considerable development of garnets. In the 

 neighbourhood of Coonoor the marked foliation and the great develop- 

 ment of garnets (see No. 9*307) are especially noticeable. It appears 

 to me to be in keeping with the few geological data available to regard 

 this great southern scarp as approximately coincident with the original 

 limits of the mass in this particular area, just as the corresponding 

 southern scarp of the Shevaroys is possibly a corresponding line limit- 

 ing that particular intrusion. In any earth movements which may 

 have taken place, it is natural to expect the great, solid masses of com- 

 pact rock forming the Nilgiris to sever connection with the very differ- 

 ent material which forms the schists and gneisses of the Coimbatore 

 plains, and this southern scarp probably, therefore, now indicates also 

 the direction of a great fault plane. Naturally the weather has scored 

 out many deep marks in this southern face and considerably modified 

 its original outlines ; but the sides are still more precipitous than 

 one would expect as the simple result of differential denudation. 

 In a separate memoir the evidences for a similar state of affairs 

 will be detailed for the Shevaroy Hills (Mem. GeoL Surv, Ind. y 



Vol. XXX, part 2), 



One of the most interesting features in connection with this 

 southern margin of the Nilgiri mass is the occurrence of large, len- 

 ticular inclusions of heavy, basic, pyroxenic rocks of a very peculiar 

 type. The lenticles are often as much as 15 feet long and 5 feet 



Pegmatoidai pyroxene across ; they are disposed in bands parallel 

 piagiociase rocks. tQ the {oliatIon of the c harnockite series in 



which they are included, and are sometimes cut through, like 

 the charnockites themselves, by the narrow dykes of olivine norite, 

 ( 68 ) 



