CHARNOCKITE SERIES 7 



and more acid — granitoid gneiss — sections, both being marked by 

 the peculiar pyroxene which they have in common. About a hundred 

 miles south, in Vizagapatam district, I have seen rocks almost exactly 

 !ike the granitoid gneiss occurring as coarse acid patches in the great 

 charnockite massif. It seems very probable that these two rock masses 

 in Kalahandi may have a common origin, such as is all but certain in 

 the case of similar rocks a little farther south. 



Basic borders have been found in several places around the margin 

 of the granitoid gneiss mass. On the north-eastern border near 

 Madhanpur more basic forms } near the intermediate charnockites, have 

 been collected, while on the west near Turkel, rocks related to the 

 Canadian anorthosites occur. (Specimens 1 5 " 1 77 i , 15*172, 15175 and 

 15-176.) 



IV.— CHARNOCKITE SERIES. 



These rocks are very prominent in the south-eastern part of Kala- 

 handi. In the plateau they are very well exposed from Moulpatna to 

 Rampur and for some distance to the east ; farther east the higher hills 

 are made up of garnet sillimanite schist, charnockite only being seen in 

 the valleys and at the bases of the hills. 



In exploring the Jeypore zemindari l it was found that the 3,000- 

 foot plateau is almost entirely made up of charnockite, which appa- 

 rently forms a great elliptical massif extending almost from the Goda- 

 vari to the Mahanadi. The charnockite occurrences in Kalahandi 

 form part of the north-western section of this massif. 



Macroscopically the rocks are usually fairly coarsely crystalline,, 

 brownish black in color, and frequently exhibit porphyritic felspars 

 and garnets. In the field a north- north-easterly parallelism or strike 

 can often be observed, conditioned by a regular orientation of the 

 felspar crystals. An examination of thin sections under the micros- 

 cope shows that the commonest form is a rock made up of plagioclase 

 orthoclase and a mineral more or less resembling the rhombic pyroxenes 

 in regard to inclusions, pleochroism and color;, but seldom extinguish- 

 ing straight along the chief lines of cleavage. Garnet, a little brown 



1 General Report, Geol. Surv. Ind., 1899-1900, p. 168. 



