

214 HOLLAND : SIVAMALAI SERIES. 



dark-coloured constituents. The felspar is chiefly microper- 

 thite. The constituents of the rock exist in the following 

 approximate proportions : — 



Per cent. 



Elseolite 34 



Microperthite ........ 56 



Magnetite ........ 3*6 



Other constituents, biotite, plagioclase, graphite, etc. . 6-4 



lOO'O 



Calcite is present in small quantities and considered to be a pri- 

 mary constituent. 

 (£) Coarse-grained "contemporaneous " veins cutting through 

 the ordinary variety, and consisting largely of elaeolite and 

 microperthite with flakes of graphite, biotite and sometimes 

 autoliths of the fine-grained ordinary form. 



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



proportion of opaque, black iron-ores with biotite. The 

 felspars are microcline and plagioclase. 



(d) A glomero-plasmatic, gneissose variety containing brown 

 hornblende and calcite, but without graphite and magnetite. 

 The calcite in this and the more basic variety (e) is considered 

 to be primary in origin. 



(e) Basic, black lenses, or sometimes dyke-like bands, with 



brown barkevikitic hornblende, calcite, purple augite, sphene 

 and graphite. The occurrence of sphene with purple augite 

 in this form is more in accordance with the commoner 

 occurrences of elseolite-syenite, but it is quite an exceptional 

 feature at Sivamalai. 

 No definite evidence is obtainable as to the age of these rocks, 

 but on account of the foliation which they pre- 

 sent it is likely that they are geologically very 

 ancient, as there is no evidence of foliation, folding, or any marked 

 earth-movement in South India since lower palaeozoic times ; the 



( 46 ) 



