238 
MANGANESE DEPOSITS OF INDIA : GEOLOGY. [ PaRT 11 : 
the appearance of the next series of sediments the ' Great Eparchsean 
interval'. The term ' Archaean ' is conveniently restricted to the 
rocks lying below this great unconformity, although, as already 
mentioned, some authors use the term as synonymous with ' pre- 
Cambrian'. 
Between the end of Dharwar and the beginning of Cambrian times 
several series of sedimentary rocks, all as far as we 
The Puraua forma know imfossiliferous, have been deposited. Such sedi- 
ments, originally deposited as sands, clays, lime- 
stones, etc., are termed Algoyikian by the Americans and Purdna by 
Dr. HoUand. ^ In areas, such as the Indian Peninsula, that have not 
been involved in any very intense folding movements since Dharwar 
times, these sediments have to a large extent escaped any serious altera- 
tion of their mineral character, and are now represented by quartzites, 
sandstones, slates, shales, limestones, conglomerates, etc. : they are 
known as the Bijawars, Kadapahs, Vindhyans, etc. 
The pre-Cambrian rocks of the Indian Peninsula can therefore 
™ .„ , , be separated into fthe ollowing divisions: — 
(.lassification of the ^ ° 
pre-Cambrian. 
I. Archaean : — 
1. The oldest gneisses (Bengal Gneiss). 
2. The schistose gneisses and the Dharwars. 
3. The plutonic intrusives, such as the Bundelkhand granite 
and the charaockite series. 
II. Purana : — 
The Bijawars, Kadapahs, Vindhyans, etc. 
From these rocks aU the later sediments, frequently containing 
fossils, and ranging in age from Cambrian to recent, 
Derivation of the . , , i i i i ^- i i 
rcxks ranging in age have been formed by denudation and re- deposition, 
from Cambrian to either chemical or mechanical ; except that a small 
portion of the detritus has been derived from 
various post-Purana intrusions of igneous rocks and extrusions of igneous 
lava-flows at the surface. 
It follows from this that, for the source of any constituent of the fossi- 
liferous rocks, we must refer, either immediately or ultimately, to the 
Archaean complex, and, within this complex itself, ultimately to the 
constituents of it that are of igneous origin ; except that a certain 
1 TransTMin. Oeol. Jnsi7lnd^., p. 48, (1900)! 
