PETR0L0G1CAL CHARACTERS. 



177 



III.-PETROLOGICAL CHARACTERS. 



The following are the principal types of rocks found associated 

 with one another in the neighbourhood of Sivamalai: — 



1. Elaeolite-syenite, consisting of— 



(a) An even-grained, foliated, grey variety which is tin 



prevalent form and contains graphite, biotite and 

 magnetite, as the dark constituents. The felspar 

 is chiefly microperthite. 



(b) Contemporaneous veins of a coarse-grained variety, 



consisting more* largely of ekeolite and micro- 

 perthite, and cutting through (a), 



(c) A granulitic form devoid of graphite, but containing 



a large proportion of opaque iron-ores with biotite. 

 The felspars are microcline and plagioclase. 



(d) A variety containing hornblende and calcite, but 



devoid of graphite and magnetite. 



(e) Basic f< Schlieren " with barkevikitic hornblende and 



calcite. 



2. Augite-syenite. 



3. Felspar-rock with corundum and other accessories. 



It is very probable indeed that this list does not exhaust the 

 catalogue of associated rocks near Sivamalai ; amongst the elaeolite- 

 syenites alone there are probably more varieties, as we were com- 

 pelled to limit the field work to a few days only, and new phases 

 of the rock turned up on nearly every day. Such variations within a 

 limited area are, however, quite consistent with the usual experience 

 amongst the elaeolite-syenite family. 



I. — Elaeolite-syenite, 



1 (a). Foliated elaeolite-syenite. 

 In Sivamalai and the small hillocks which are aligned to the 



( 9 ) 



