10 WALKER; GEOLOGY OF KALAHANDI STATE. 



The remarkable thing about this analysis is the very high propor- 

 tion of silica and alumina as compared with the insignificant nropor- 

 tion of alkalies. Chemically it does not resemble any known igneous 

 rock, though rocks of this chemical composition could be obtained by 

 the metamorphism of well leached clay mixed with a little quartz. 



The composition of the sillimanite schist taken along with the 

 nature of the rocks with which it is associated compels one to regard 

 this group as para-schists, while their occurring above the charnock- 

 ites, granitoid gneiss and other coarse gneisses, all of which appear 

 to be igneous in origin, suggests that we are dealing with rocks 

 formed by the metamorphism of ancient sediments, very probably by 

 the intrusion of the great igneous masses referred to, and by the 

 action of a mountain building force acting in a line at right angles to 

 the north-north-eastern foliation frequently observed in the rocks of 

 Kalahandi state. In this case we must regard the sillimanite schists 

 as older than either the charnockite or the granitoid gneiss and even 

 older than many of the gneisses of the crystalline complex. 



Mr. Smith found these schists over a great part of the Ganjam 

 Malias, 1 and I have observed them farther south along the eastern 

 border of the eastern Ghauts in Vizagapatam district. Apparently 

 these isolated outcrops are remnants of a once continuous arch of 

 altered sediments covering the great igneous massif of charnockite 

 and related igneous rocks which extends almost from the Godavari to 

 the Mahanadi. At present these rocks are known to occur as hills on 

 the 3,coo-foot plateau, which is composed essentially of charnockite* 

 and as a fairly broad border along the northern and eastern margins of 

 the massif. For some reason, as yet unexplained, sillimanite schists 

 do not occur along the western margin in the vicinity of Jey- 

 pore. There are, however, evidences indicating a faulted western 

 boundary for the charnockite ellipse, in which case the upthrow of 

 the schists would expose them to denuiatioo, which may account for 

 their absence along the western side of the massif. 



1 Genera Report, Ge.J. S.irv. Inj., '.899-1930, p. 153. 



