Reports & Proceedings — Geological Society of London. 229 



representatives of the Huroiiian would be non-existent. Obviously, 

 therefore, the Mysore Archaean succession was either very incomplete 

 or it did not fit in with the classifications of Holland and Lawson. 

 It was to be remembered that Holland's classification dealt witli 

 a much wider area than Southern India, and the essential problem 

 appeared to be whether his Bundelkhand gneiss (Laurentian) and the 

 Bengal gneisses (Keewatiu) were really older than, and unconformable 

 to, the Dharwar System — as represented by him — or whether they 

 were post-Dharwar eruptives corresponding to portions of the Mysore 

 gneissic complex. In favour of the latter view it was noted that 

 observers acquainted with both have appeared to recognize the 

 Bundelkhand and Bengal types of gneisses in and around Mysore, 

 and that all of these gneisses have, until recently, been regarded 

 as forming part of the great Fundamental Gneissic Complex of India. 



The Lecturer then described the map of Mysore, which, on a scale 

 of eight miles to the inch (1 : 506,880), presented a simplified 

 summary of the work of the Mysore Geological Survey. On 

 lithological grounds the Dharwar System was divided into an Upper 

 and a Lower Division. The former was composed largely of basic 

 flows and sills with their schistose representatives. Whether some 

 of the chloritic schists, slates, phyllites, and argillites were of 

 sedimentary origin was still doubtful. In the series as a whole, 

 chlorite predominated and hornblende was subordinate. The 

 presence of carbonate of lime, magnesia, and iron was a strikingly 

 pi'evalent feature. The Lower Division was composed of dark 

 hornblendic epidiorites and schists, which were distinguishable from 

 the greenstones of the Upper Division by their dark colour and 

 practical absence of chlorite. Many of the greenstones and schists 

 of the Upper Division appeared to resemble Keewatin rocks of Lake 

 Superior, such as the Ely Greenstone series (save that augite is 

 conspicuously absent in the Mysore rocks), and it had been suggested 

 that the dark epidiorites, which naturally crop out between the 

 rocks of the Upper Division and the intruding gneisses, might be 

 merely metamorphosed portions of the greenstones and chlorite- 

 schists. This might be true in some cases, but the independent 

 existence of the dark hornblendic rocks of the Lower Division was 

 supported by the fact that they do not exist in many places where 

 the gneisses come into contact with the greenstones ; that many of 

 the former retain original igneous structures, which would be 

 unlikely to survive the chloritization and the subsequent change to 

 epidiorite ; and, finally, that the amphibolitization of the rocks of 

 the Lower Division appears to have been complete before the 

 intrusion of the earliest of the gneisses which, with its associated 

 pegmatites and quartz-veins, has developed secondary augite in the 

 hornblendic rocks along intrusive contacts. 



The Lecturer referred briefly to the autoclastic conglomerates 

 which were usually associated with intrusions of the Champion 

 Gneiss, to the intrusive character of some of the quartzites or quartz- 

 schists, and to the evidence that the limestones were, partly, if not 

 wholly, due to metasomatic replacement of other rocks by carbonates 

 of lime and magnesia. 



