Preanger

The Waterberg system is the youngest of the pre-Cambrian. The rocks are mainly of sandstones and rest unconformably on the Transvaal. The Torridonian of Scotland compares with it. India.—The pre-Cambrian of India consists of two main groups (a) a great mass of gneisses, crystalline schists, and plutonic rocks, named by T. H. Holland the Vedic, and (b) a group of unfossiliferous sedimentary rocks named by Holland the Purana group and suggestive of the Animikean and Keweenawan of Canada. Group (b) includes many isolated areas of sediments, of great thickness, little disturbed and resting with great uncon formity on the Vedic group. Holland has tentatively classified the Vedic rocks as follows, commencing with the youngest :-5, Post-Dharwar, eruptives; 4, Dharwar systems; 3, Bundelkhand type of deformed eruptives; 2, Bengal type of Schists; 1, oldest gneisses.

There appear to be at least two periods of granitic intrusions, one (the Bundelkhand) cutting the Bengal schists, and the younger (post-Dharwar eruptives) cutting the Dharwar system. It has been cautiously suggested that the Bundelkhand granites may be comparable with the Laurentian of Canada, and the post Dharwar eruptives with the Algoman of Canada. The Bengal Schists are thought to be comparable with the Keewatin of Canada. The Dharwar system is much altered and folded, and contains lava flows, and banded jaspers characteristic of the Keewatin iron formation of Canada; sediments possibly corres ponding to the Timiskamian may be recognized when further work is accomplished. The chief gold mines in India, those of the Kolar gold field, occur in rocks belonging to the Dharwar system. The post-Dharwar eruptives include granites and the elaeolite-syenites of Coimbatore.

Western Australia.

In the pre-Cambrian rocks of Western Australia no general sequence has yet been established, although in restricted areas the age relationships have been worked out. The rocks consist dominantly of gneisses, schists and granites ; amphibolites everywhere play an important part, and bands of chert and brilliantly coloured jaspers constitute noticeable fea tures and are identical with those in India, Rhodesia and East Transvaal.

The crystalline schists, some of which bear a close resemblance to the Keewatin of N. America, are divided into two groups : (a) an older group made up of mica-quartz-schist and marble asso ciated with basic rocks which have in certain localities been con verted into greenstone-schists, and (b) a younger group of con glomerates, arkoses, quartzites, slates and phyllites (the Mosquito Creek and other series). They have been intruded by great

batholiths of granite covering some hundreds of sq. miles.

A younger series of little altered rocks, known as the Nullagine formation, consists of sandstones, quartzites, conglomerates, and dolomitic limestones, together with a series of lavas, ashes and agglomerates. The beds generally repose at horizontal or inclined angles, and rest with great uncomformity on the older rocks.

Brazil.

The pre-Cambrian covers large areas in Brazil, but little detailed work has been done. The oldest rocks have been named Archaean and consist of gneiss, granite and schist. There are also metamorphosed sediments, classed as Algonkian, made up of quartzites, iron formation, argillaceous schists and limestones. These Algonkian sediments contain great deposits of iron ores. One of the deepest gold mines, the Morro Velho mine of the St. John Del Rey Mining Company, occurs in pre-Cambrian cal careous schists and slates.

China.

In China there is a basal group of rocks consisting of gneisses and schists, including green schists, to which the name T'ai-shan complex has been given and which may correspond, in part, with the Keewatin of the N. American continent. The T'ai-shan complex is intruded by granites. Resting with great unconformity on these rocks is a highly altered, folded series of sediments known as the Wu-T'ai system, the conglomerates of which contain granite pebbles, proving the existence of granite older than this system. There are believed to be unconformities within the Wu-T'ai system ; and granites are intruded into it. Some of the more altered sediments of the Wu-T'ai are suggestive of Lower Huronian rocks of the Lake Superior region.

Overlying the Wu-T'ai rocks with marked unconformity is the little altered Hu-t'o system, consisting of conglomerate, quartzite, shale and limestone. The Wu-T'ai and Hu-t'o systems have been classified by Bailey Willis as Proterozoic. (C. W. K.) BIBLIOGRAPHY.—General. L. V. Pirsson and C. Scuchert, Textbook of Geology (2nd ed. 1919, vol. ; F. R. C. Reed, Geology of the ish Empire (1921) ; Sir A. Geikie, Textbook of Geology (4th ed. 1923) ; "Pre-cambrian rocks of the world" (Br. Ass. Ad. Sc., Toronto, 1924), Journal; "Symposium on pre-Cambrian Geology" (Bull. Geol. Soc. Am., vol. 38, Nos. I and 4).