32 MIDTDLEMTSS : THE GEOLOGY OF IDAR STATE. 



though rarely, the Delhi Quartzito must not be lost sight of in 

 considering their mode of origin and age. 



It is not at present known to me whether or not these generally 



acid hypabyssal vein rocks are now in any 



No visiblo connection direct connection with large plutonic masses, 



with largo masses. . • i . i j±i 



with which they might be assumed to be 

 genetically related and from whose magma they presumably may 

 have been differentiated. From first impressions there was a dis- 

 position to associate most of them with the large masses and stocks 

 of the granite that has already been referred to and which will 

 later on be described under the name of the Idar granite ; but, 

 opposed to this are many and serious objections. For instance, 

 these aplite veins in the calc-gneiss are considerably different from 

 the Idar granite, not merely as regards the scanty ferro-magnesian 

 minerals (which show striking differences and are more varied), 

 but also as regards the felspathic constituent of the eutectic which 

 is considerably different in colour, and especially so in the thicker 

 and more massive examples of thorn which occasionally present 

 themselves ; secondly, their outcrop areas are nearly always dis- 

 tinct and separate from those of the Idar granite, and there is nothing 

 to suggest the passage of the one rock into the other on the ground, 

 whilst, thirdly, at those few places where the outcrops of the aplite 

 and Idar granite do approximate, the massive Idar rock is found 

 to cut across and truncate the veins and veinlets of the other. 

 Lastly, these aplite veins seem to have had their inception among 

 the calc-gneiss about the period when the latter was bent into its 

 larger earth folds ; whereas, from the evidence of the truncated calc- 

 gneiss and from other evidence, there is reason to believe that the 

 large irregular bosses and stocks of the Tdar rock were altogether 

 posterior to such diastrophism. 



We are forced to conclude then that these aplites, so far as at 

 present exposed at the surface of the country, have no visible 

 plutonic stock into which we can trace them, though we may, if 

 we wish assume one at present buried out of sight at some depth 

 below its vein equivalents. Further remarks on the debatable 

 question of their origin will be found later at the end of this section 

 when summarising the origin of the veins and the intruded gneiss. 

 Though occasionally appearing in rather thick elongated ex- 

 posures — as already remarked, some 50 feet 

 thick and upwards — their more usual role is 



