I9 2 HOLLAND : SIVAMALAI SERIES. 



form, graphite and zircon. The felspar and graphite show a ten- 

 dency to concentration along certain lines to the exclusion of the 

 elaeolite ; these are coarser in grain than the portions in which the 

 elaeolite is concentrated. The pink elaeolite often shows the com- 

 mencement of alteration, with the production of hydrated products ; 

 but the change is quite insignificant and probably only superficial. 



I (c). Variety containing microcline and plagioclase, but without 



graphite. 



, This type is based on specimens collected by Mr. Middlemiss 

 in 1895 from the western extension o£ the Sivamalai range (No, 

 10,385). The principal points in which it differs from i(a) are, first, 

 the absence of graphite, and, second, the presence of microcline asso- 

 ciated and often intergrown with a well twinned plagioclase. The 

 opaque iron-ores, which are chiefly titaniferous magnetite, are also 

 relatively more abundant than in the other types. The microper- 

 thite so characteristic of i(a) and 1 [b) occurs in very small quantities 

 only and is always of a coarser type, the spindle-shaped inclusions 

 being easily distinguished with the low power. 



The plagioclase is remarkably fresh and shows very sharply 

 defined twin-lamellae. The maximum angle between the positions of 

 extinction in the albite lamellae is 20 , which would be true for either 

 albite or andesine, but in a rock too fine-grained for the isolation 

 of the constituents the species cannot be stated with certainty, 

 Albite would, however, be more consistent with this association, 

 and has been found presenting similar characters in other occurren- 

 ces of elaeolite-syenites, and it has been identified in the associated 

 felspar-rocks, Rosenbusch mentions that albite sometimes accom- 

 panies older, well corroded crystals of microcline-perthite, and some- 

 times forms narrow borders around the latter mineral. 1 



1 Mikroskop. Fhys. der mass, Gest. (1896), p. 151. 



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