LIST OF FORMATIONS. 5 



the Phvllite series and the Delhi Quartzite doubtfully with the 

 Purana group, and the Aravallis probably rather high up in the 

 Archaean, it is necessary to arrange these two systems according 

 to a purely local classification only, or at least to one that they 

 share in common only with Rajputana. 



This poverty in formations of the ordinary Geological Record 

 does not, however, connote dearth of interest, except in the domain 

 of palaeontology ; for these representatives of the Purana and 

 Archaean, together with the igneous rocks penetrating them, as 

 laid bare in this part of India, present a wonderful variety of type 

 both mineralogically and structurally, and afford fascinating pro- 

 blems in the study of the earth's deeper crust that become the more 

 absorbing as we realise the great principles at stake in the matter 

 of their complex origin. 



ARAVALLI SYSTEM. 



Preliminary Remarks. 



In the interests of an orderly geological description progressing 

 upwards from the older to the younger rock 

 A difficult and elusive seri ft rfQ fe necessary to open the de- 

 complex. . • . " -it 



scriptive part 01 this paper with what is 



certainly the most difficult, most complicated, and perhaps the 

 most elusive of all the rock systems exposed in Idar, namely, that 

 phase of the metamorphic and crystalline Archaean complex for 

 which the name " Aravalli System " has here been intentionally 

 reserved, in spite of certain vaguenesses in the later application 

 of the term. 



The term Aravalli System was established by C. A. Hacket 1 



for certain rocks exposed in the Aravalli 



The oame -Aravalli." ^^^ oi ^ of R j^y metam orphic and 



crystalline character. Furthermore, the above author, not only 

 applied the term to those rocks as above stated, but actually carried 

 his mapping continuously along the line of strike from that, their 

 first-described home among the roots of the old Aravalli range, 

 down into connection with those herein named Aravalli in Tdar 

 State. It is, no doubt, also true that the same observer similarly 

 correlated other more doubtful sequences of metamorphic rocks, 



1 Sec, OeoL Surv. India, Vol X, p. 84 (1877). 



