ARAVALU SYSTEM. 43 



calcareous rocks (on a relatively small scale) makes it verbally 

 intelligible that such an all-round metamorphic transformation of 

 great thicknesses might conceivably have taken place. In support 

 of this it is only necessary to allude in passing to such well-known 

 instances as those of the Coniston limestone and Mountain lime- 

 stone in contact with the Shap granite and the Whin Sill respec- 

 tively, so carefully worked out by Harker and Marr 1 to establish 

 the fact that very similar sets of highly altered calcareous rocks 

 with identical contact minerals may locally, and on a small scale, 

 be produced from what is elsewhere a sedimentary series among 

 the historical rocks. Unfortunately in India, wherever calc-gneisses 

 (including crystalline marble beds) of the character of those above 

 described in Idar, have been found, they never, so far as I know, 

 have been traced across the country into any unmetamorphosed 

 and easily recognisable calcareous sedimentary series ; and the con- 

 verse of this is equally true in those areas of (for instance) Vindhyan 

 and Cuddapah rocks, where, over enormous areas to be reckoned 

 in hundreds of miles, definitely stratified sedimentary series 

 embracing calcareous, shaly and arenaceous deposits, in clean and 

 well-defined horizons (notwithstanding their containing no fossils) 

 equally never show any local passage into rocks in any way resem- 

 bling those here defined as calc-gneiss. Whether, then, we con- 

 template these calc-gneisses of the Aravalli region, those of Coim- 

 batore and Salem in Madras, those of the Central Provinces described 

 by Fermor and Burton, or those of Vizagapatam or Burma, we are 

 obliged to admit that so far there has appeared no particular proof, 

 adequately linking each of them with any clearly avowed sedimen- 

 tary series. Hence, in the past, attempts have been made 2 to ex- 

 plain much of the crystalline limestone and calciphyre content of 

 such calc-series by referring them to alteration effects of lime- 

 bearing silicates of an original pyroxenic orthogneiss, whose nature 

 is necessarily assumed to have been deep-seated and magmatic. 

 Such views, however, are not much in favour at present, so that 

 I propose at once to examine the question from the more con- 

 servative standpoint of the Idar calc-gneiss being a metamorphic 

 sedimentary series — a supposition that will also receive important 

 support later on when the Mundeti series of allied calcareous rocks 

 is described (see p. 53). 



1 Q. J. G. &, xlvii (1891), p. 266. 



1 Judd and Barrington Biown, Phil Trans. Roy. Soc. Vol. 187 A, p. 205, 



