AKAVALLI SYSTEM. 55 



rock, one of which is a more or less compact or finely crystalline, dark 



grey limestone, another a compact, hornstone-likc rock, of from 



white to grey and dark greenish-grey colours, and a third a black 



slaty rock, particularly well seen, intcrbedded with the preceding 



types, 1 mile tt.W. of Sisasan and also in the little ridge N.E. of 



Phechania. There is one more type of sandy rock, that is worked 



and exported for making hones, found near Malasa. 



Taking for descriptive purposes these varieties in order, the more 



calcareous kind such as A 1 '., (12341), from 

 Calcareous variety. n f,.,, f , .,, , ,_., ,, »i ,i i- t« , • 



S.S.W. of hill 1153, three miles north of Mnndeti, 



is a dark, banded, grey rock, fairly compact, looking rather like 

 the limestone that constitutes the basis of the Kherod series, but 

 not so crystalline. In thin section under the microscope it is seen 

 to be a very finely equidimensional, granular rock, composed of 

 what appears to be equal amounts of minute granules of diopside 

 and calcite, a small percentage of quartz or {() quartz-felspar mosaic, 

 and a few minute plates of biotite and aggregates of iron-ore (pyrite). 

 The grains of calcite are seldom large enough to show typical 

 rhombic cleavage and twinning, as is universal in the calc-gneiss 

 and amphibolite-limestone, but these can occasionally be dis- 

 tinctly made out with high powers near the edge of the thin section. 

 The very high order interference tints and moderate relief are every- 

 where sufficiently characteristic of calcite grains, just as the behavi- 

 our of the rock itself in the field and its reaction with cold acid is 

 also characteristic of limestone. 



The very pale, bluish-green, highly refracting and moderately 

 doubly refracting grains, that I consider to be very small diopside 

 grains (coccolite), have all the appearance of minute grains of 

 diopside as seen in the calc-gneiss of the Vadali neighbourhood, 

 but no cuhedral shapes or cleavages other than irregular cracks 

 can be seen. Large interlocking " filigree : ' areas of these grains 

 include within themselves granules of calcite and quartz and fre- 

 quently behave as single ophitic or poikilitic crystalline units, 

 extinguishing together and showing uniform interference colours, 

 after the manner of the " filigree " amphibole crystals in the Kherod 

 series. Wherever these areas show any tendency to elongation the 

 extinction angle is wide, as would be characteristic of pyroxene 

 rather than amphibole. 



The plates of biotite are similarly ragged and frequently enclose 

 grains of calcite, the pleochroism being very pale straw-colour 



