•22 uiDDl.KMlss : THE ttEOLOOt Of IDAU STATE. 



report by the author) in regard to the content of quartz, 

 microcline. plagioclase, bright green augite (diopside), sphene, 

 scapolite and calcite. But in these latter rocks garnet is represented 

 by melanite or colophonitc instead of grossularite, and epidote 

 takes the place of zoisite, whilst there is a much greater develop- 

 ment of scapolite. Typical examples of these from near Madukarai 

 railway station near Coimbatore are nos. ^ 2 . 2 , ^^ and j 1 /,, 

 collected by the author. 



Similar calc-gneisses undoubtedly occur in Vizagapatam. 



It would be premature to offer any remarks yet on the question 

 of the origin of the calc-gneisses of Idar. The 

 Question of origin particular question relative to these examples 

 is necessarily bound up with the general 

 question of the origin of the calc-gneisses of other parts of India, 

 certain important conclusions regarding which have recently been 

 stated by Dr. Permor, 1 so that the subject requires comprehensive 

 treatment. Anticipating, also, that any explanation offered of the 

 Idar occurrences must also include a consideration of the associated 

 gneisses as well as of the intrusive aplite veins that are found pene- 

 trating them, it will be well to postpone remarks under this heading 

 until after those other important and connected rock masses have 

 been described. 



(2) Non-calcareous Biotite Gneiss, associated with the Cal-gneiss. 



Here I propose to describe a gneissic rock series, of rather limited 

 extension, that is developed in close associa- 

 GeneraJ distribu- t [ on w j tn t } ie calc-gneiss. Flanking the chief 

 calc-gneiss areas on their eastern margins, and 

 in juxtaposition with them, there come smaller areas of generally 

 non-calcareous gneiss or schist, composed in the main of biotite 

 and quartz. The foliation planes of the gneiss are perfectly con- 

 cordant with those of the calc-gneiss, and they follow on them in 

 a way which suggests direct sequence. This is apparently con- 

 firmed by the general appearance and lie of these rocks and the 

 kind of undulating country which they oomposej as well as by the 

 fact that they are penetrated by intrusive veins of granite aplite 



1 Progress Report for 1912-13 and 1914-15 summarised in the (ieneral Report of the 

 Survey for 1914, Bee., Q. S. /.. Vol XLV, pi 2. 



