A RAVALLI SYSTEM. l5 



pyroxenes rather than of fche aluminous augites. Its colour and 

 general habit, and its presence in a matrix of 80 much caloite 

 are in accordance with this. Jn the scapolitic variety (A* 5> 12138) 

 from Proia, presently to be described, some richer bands of pvroxene 

 (12139) and sphene present typical elongated, and generally idiomorphic 

 grains of this mineral from which it can more definitely be deter- 

 mined as diopside (see p. 10). 



Returning to the rock H miles north of Vadali ( 3 v' 7 ). there 

 is also some small amount of dark mica in isolated plates sometimes 

 more or less gathered together, giving pale yellow to light brown 

 pleochroism. Sphene is also a prominent mineral component in 

 irregular elongated grains with rounded edges, and there are a 

 few grains of scapolite. The iron ore sparingly developed is pyrite. 

 Felspar is almost absent in this particular rock, but there are a 

 few grains of microcline and some quartz in relatively small amount. 



From this summary of the mineral contents the rock clearly 

 emerges as a grey impure marble with diopside as the chief accessory. 



Although felspar is absent, or nearly so. in the aboye rock, in 

 another specimen from the same locality (sV's- 12131). and which 

 to the eye is very similar, there are fairly abundant grains of micro- 

 cline. whilst biotite is absent (PI. 8. fig. 1 , nicols crossed). 



Some 5 miles away to the north-west, at the south end of the 

 Dharol hill, occurs a variety of the calc-gneiss (//'c,. 12132, PI. 8, fig. 2) 

 i?i which a very large proportion of the diopside is replaced by uralitic 

 hornblende in hypidiomorphic grains, and there is a large amount 

 of quartz, orthoclase and plagioclase (? labradorite). but no microcline, 

 although c; 'cite still remains a prominent mineral. The uralitic 

 hornblende, which sometimes shows its crystal outline fairly well, gives 

 extinction angles (Z A c) up to about 18°. and the pleochroism 

 comes near that of actinolite. being Z pale bluish-green. Y yellowish- 

 green and X pale greenish-yellow. The orthoclase. though per- 

 fectly clear, is frequently easily distinguished by characteristic 

 cleavages from the quartz, but there are some small grains of otic 

 or both that remain undifferentiated. There are also detected 

 in the thin slice of this rock a very few ragged and irregular or 

 corroded plates of a, mineral with a considerably high refractive 

 index, near or a little above that of the diopside in the same slide. 

 Its interference colours are of a very low order, being a pale indigo 

 or pale violet-gray, and which, working from the quartz in the 

 same slide, indicate a birefringence of about -006. It contains 



c2 



