Reviews — Geological Survey — Geology of India. 125 



Pre- Cambrian. — The great unfossiliferous Viudhyan system, so 

 important a feature in Central India, has attracted some attention of 

 late from the Indian Survey, and Mr. Vredenburg has even suggested 

 a new classification, though perhaps only provisional. Into these 

 details we need not enter, but there is one subject in connection with 

 the Vindhyans to which some allusion might be made, viz., the 

 Diamantiferous Conglomerate occurring in the Eewa division of the 

 Upper Vindhyans near Panna in Bundelkhand. The diamond 

 industry in India at present is only a small affair, and therefore the 

 subject is unimportant from an economic point of view. Yet the 

 occurrence of the diamonds otherwise than in an ordinary alluvial 

 gravel is interesting, as possibly tending to throw some light on the 

 origin of the gem. For this purpose it will be necessary to study the 

 geological conditions under which the Diamantiferous Conglomerate 

 occurs. The Archaean base of the country is held by a Granite, 

 which, even if newer than the Aravalli system, is the oldest rock in 

 Bundelkhand. This Granite, where exposed, is seen to be seamed by 

 quartz-reefs, and these again are cut, approximately at right angles, 

 by linear dykes of basic igneous rock. These dykes appear to 

 represent a period of volcanic activity contemporaneous with the 

 Bijawar system, an unfossiliferous sedimentary formation which, in 

 places, intervenes between the Granite and the Lower Yindhyans. 

 In Southern India similar dykes of the same age occur abundantly 

 in the neighbourhood of diamond-bearing deposits like those of 

 Bundelkhand, "an association which suggests some possible genetic 

 relation." The Bijawars were extensively disturbed before the 

 deposition of the Vindhyans, which partly rest upon them quite 

 unconformably. Their denudation supplied the Vindhyans with 

 a vast amount of material, the bright-red pebbles derived from the 

 bedded jaspers and fault-breccias being particularly conspicuous in 

 some of the Vindhyan conglomerates, which likewise contain 

 a peculiar jaspery sandstone of a greenish colour derived from the 

 denudation of a portion of the Lower Vindhyans. 



Having discussed the probable origin of the material, Mr. Vredenburg 

 next proceeds to define the position and mode of occurrence of the 

 diamond-bearing deposits. There are two thin conglomerates (seldom 

 exceeding two feet) in each case capping sandstones and underlying 

 shales, of which the lower one is the best known and the most 

 important. The pebbles of the Lower Rewa conglomerate are derived 

 partly from the quartz-reefs of the Bundelkhand Granite, partly from 

 the Bijawars and Lower Vindhyans. Fragments derived from these 

 two sedimentary formations are absent from the Upper Eewa con- 

 glomerate, which only contains pebbles of vein-quartz. These quartz 

 pebbles derived from the granite area are therefore the essential 

 associates of the diamonds, " and the original home of the gem must be 

 one of the rocks of the granitic region, either the Granite itself, or its 

 quartz reefs, or the basic dykes." Further on, however, Mr. Vredenburg, 

 commenting on the presumed absence of diamond workings in the 

 Bijawar conglomerates, both in Central and Southern India, suggests 

 that the diamonds are not older than the Bijawar, " which supposition, 

 coupled with their evident derivation from the crystalline area, points 



