APPENDIX. 79 



completely granulitic condition, which may also, from the abundance and even dis- 

 tribution of the felspathic constituents, be referred to the class of altered diabases j 

 but the larger number of specimens are of doubtful origin, retaining no peculiarity 

 of structure or of composition sufficiently well marked to definitely refer to any 

 known more recent type. The general composition, judging from microscopic 

 examination, is about the same as one would expect as the result of the metamor- 

 phism of a basic ash, but without chemical analyses it would be unsafe to refer the 

 hornblende schists to such an origin. The presence of undoubted basic igneous 

 types amongst the schists, however, settles the origin of some of the bands, and it 

 is highly probable that they were originally basic flows accompanied by ash beds 

 whose metamorphism would then account for the remainder of the hornblende 

 schists. 



Pseudo- conglomerates. 



Specimens from one locality, Pedpalli, contain numerous isolated lumps of 

 gneiss, not generally rounded but more often lens-shaped, and firmly cemented 

 in the matrix by marginal intercrystallization. The fragments of gneiss are em- 

 bedded in bands which are of a more felspathic and gneissose character than the 

 average hornblende schists, and occasionally angular fragments of the latter, as 

 well as of quartz-iron-ore rocks, are included in these gneissose bands. These 

 rocks present many of the characters described by different authors — C. R. Van 

 Hise, H. L. Smyth, A. E. Barlow, and others— as due to the autoclastic (Smyth) 

 deformation of some similar types amongst the American pre-Cambrian rocks. The 

 fragments of granite-gneiss and the gneissoid bands are probably related to one 

 another, and due to the brecciation of an old granitic intrusion together with 

 the hornblende schist, which it invaded. Basing his estimate on Prof. Hoskins* 

 experiments on the flow and fracture of solid rocks, Van Hise 1 assumes that the 

 zone in which autoclastic rocks may be produced is confined to the outer 10,000 

 metres of the earth's crust, and that the formation of widespread autoclastic rocks 

 is probably limited to the outer 5,000 metres. The preservation of the individu- 

 ality of the fragments in this Kolar autoclastic conglomerate shows that deformation 

 occurred above the " rock-flowage " level, whilst the complete crystalline cement- 

 ation of the whole points to deformation under great pressure. In essential points 

 these rocks differ from true conglomerates, though it might be difficult to distinguish 

 this kind of material from conglomerates which have been mutilated by dynamic 

 action: the real criteria must be checked in the field, for which purpose the sub- 

 joined notes on the rock fragments constituting one of the large specimens may be 

 of service : — 



Sections from different parts oj the pseudo-conglomerate :— (1) Areas of coarsely granular 

 clear quartz in a matrix of fine granulitic quartz and felspar, with numerous shreds of green- 

 brown biotite and colourless muscovite. Large felspars much damaged on their borders and 

 with numerous secondary brightly polarising inclusions. The section is not essentially unlike 

 some of the supposed older biotite gneisses of South India ; but in other sections this granite- 

 gneiss shows sphene and epidote as is the case with the prevalent granite-gneiss of the area. 



(2) Section across the junction of a piece of granitoid gneiss and a thin hornblende schist 

 streak separating the granitoid gneiss from a quartz-iron-ore band. The hornblende schist 



1 Principles of North American Pre-Cambrian Geology, p. 679, 



