THE GARNET SILLIMANITE SCHISTS— KHONDALITE. 



9 



nite schist. Frequently the hills are flat topped and crowned with a 

 sheet of laterite from 80 to 200 feet in thickness. 



The usual strike is north-north-easterly. Where the Khonds have 

 not cut down the forest in clearing land for cultivation, hills composed 

 of sillimanite schist are usually well wooded, the gently sloping hill- 

 sides being covered with loose blocks of various sizes rendering it 

 difficult to obtain large outcrops of these rocks for geological study. 



Along with the sillimanite rocks, probably interbanded with them, 

 occur occasional masses of garnetiferous quartzite and of a white rock 

 resembling crystalline limestone but which the microscope shews to be 

 made up of a colourless pyroxene (wollastonite ?), a greenish pyroxene, 

 probably diopside, green spinels, brown garnet scapolite and sometimes 

 calcite and sphene, all minerals which are frequent and characteristic 

 of crystalline limestone formed by the metamorphism of slightly impure 

 limestone either by regional or contact action. The essential differ- 

 ence between the rock in question and the ordinary marble consists in 

 the large r61e played by calcite in the latter and its very subordinate 

 proportion in the former. The more impure the original limestone, 

 the greater the rfile played by the accessory minerals. Judged from 

 this point of view we may conclude that the rocks under discussion 

 were probably produced by the metamorphism of extremely impure 

 calcareous sediments. (Specimens 15*216, 1521 7, 15*218 and 15*219,) 



Unfortunately none of these impure marbles have been chemically 

 analysed. 



Specimen 15*181, which I regard as a typical garnet sillimanite 

 schist, yielded on analysis— 



SiO., 





t « * 



, 



• 74-17% 



Al 2 t) 3 . 





. 





. 17-16% 



Fe 2 3 . 







, 



, 7'82% 



MgO . 





. 



, . 



. -83% 



CaO 





. 



. 



•61% 



K 2 





. . 





. trace. 



Na 2 . 





. . 



, 



• -49% 



Loss on Ig 



nition 



rOTAL 



•11% 





. 101*19% 





S 



G. 



. 2'9I 





