74 ailDDLKMlSS: Till'. (1K0L0GY OF IDAR STATE. 



It cannot be said that this occurrence of a nearly pure diopside- 

 rock surrounded by vein-quartz simplifies the matter by throwing 

 any light OD the question of the origin of these curious pyroxene- 

 bearing rocks. 



It is not possible to coordinate the widely separated outcrops 



(and their strikes) of the Aravalli rocks genera- 



Stauotaral 1 eaturee. ^ oyer ^ whol(1 ()f this B ama , UV ada-Jesang- 



pur area, or to say more than can be seen by an inspection of the 

 map. Wherever prominent master-strikes are indicated, they are 

 sometimes more or less parallel with the run of the neighbouring 

 Delhi Quartzite ridges ; but at two notable places, namely, ( 1 ) 

 the Meshva river near Kavadia and Vajapar. and (2) the neighbour- 

 hood of Menu the discordance is so striking as to be remarkable, 

 and— as will be pointed out later when describing the Delhi Quartzite 

 —this is of the very greatest importance in discussing the relation 

 of these two great rock systems to each other. 



DELHI QUARTZITE SERIES. 



(i) Preliminary Remarks. 



The above name, taken from Market's terminology, seems 

 fairly appropriate as applied here to the 



Nomenclature. ^ massive set of quartzite rocks which form 



an important, and generally the lowest visible, member of a second 

 great system which overlies the lirst-descrihed Aravalli. There is 

 no doubt that Hacket used the term far these very rocks and mapped 

 them down to as far south as latitude 24°, that is to say, touching 

 the northern part of the present described area. Moreover the 

 strike continuity of this characteristic and massive formation can 

 be recognised right through the area, mapped by Hacket in Raj- 

 putana %nd recently revised by Heron) until, after coinciding 

 with the Alwar quartzite, its last and most northern portion finally 

 tails out in the Ridge at Delhi itself, preparatory to disappearing 

 under the Gangetic alluvium. 



If we exclude all the smaller inequalities of the surface and the 



flat plains in Idar State, wherein are deve- 



A high-lying contrast- ] ^ G ^ the Aravallis as already described. 



ing formation. together with the distinctive, isolated, rugged 



peaks of the Idar intrusive acid rocks, whose description will follow 



