The Geology of the Transvaal 1

Abstract

THE most interesting features of the report of the Transvaal Geological Survey for the year 1906 are the excellent pieces of detailed mapping of the rocks of the Transvaal System, in the Lydenburg district, between Lydenburg and Belvedere, by Mr. A. L. Hall, and in the area immediately east of the Crocodile River and south of the Rooiberg by Mr. W. A. Humphrey. These two districts form parts of the same great synclinal trough; but while the Lydenburg district is at the eastern end of the trough, and is as remarkable for the simplicity of its geological structure as it is famous for the grandeur of its scenery, the area mapped by Mr. Humphrey lies 200 miles to the west and nearer the centre of the trough, and is characterised by an exceptionally complicated structure. Surrounded by the much later Red Granite formation, the isolated inliers of the Transvaal System in the latter area owe their position to faulting and folding on a large scale, an adequate explanation of which can only be forthcoming when the area to the west is mapped in detail.