Professor T. Rupert Jones — Geology of W. Swaziland. 105 



the continental slope, could be shown to contain deposits resulting 

 from continental degradation, it would be difficult to maintain that 

 no dry land had existed where now are oceanic depths ; but failing 

 such evidence as this, we must be content to regard the deep Polar 

 ocean as a permanent feature. 



Again, as a more especial argument for breaking up the existing 

 North Polar basin, it has been pointed out that the strike of the 

 rocks and the trend of the mountain chains for the most part run 

 north and south, ending abruptly on its margin. The idea is that 

 these mountain chains, having what is called a ' Ural orientation,' 

 once extended further north, and have in some unaccountable way 

 been removed or cut short. Undoubtedly, we know so little of the 

 true termination of these highland areas that no theory can safely be 

 founded on their apparent truncation. There are, however, other 

 regions where a mountain range is obviously truncated by the sub- 

 oceanic continental slope — notably the Cantabrian chain in the north 

 of Spain, which may be said to disappear suddenly in 2,000 fathoms 

 of water. As a possible explanation I would suggest that such 

 disappearance is due to tectonic failure in the process of mountain- 

 making, such mountain - making being especially connected with 

 continental elevation. On approaching the margin of an oceanic 

 area another set of tectonic conditions prevails. In this way the 

 mountain range fails fx'om internal causes, and, therefore, any theory 

 accounting for its removal becomes superfluous. 



[To be continued.) 



11. — Notes on the Geology of West Swaziland, South Africa. 

 By Professor T. Eupert Jones, F.R.S., F.G.S. 



MR. SYDNEY RYAN, of Darkton, Managing Director of the Ryan 

 Tin Mines, situated on the Embabaan River in West Swaziland, 

 has collected and sent to England a large collection of rock-specimens 

 from the Ingwenya Berg, the dominating feature of the district. 

 He has also provided plans and sections of the district, which are 

 here partly reproduced. The specimens have been presented to the 

 Mineralogical Department of the British Museum, together with 

 a complete catalogue, having reference to the Sections referred to 

 above, and indications of the lithological characters of the 140 speci- 

 mens.^ Mr. G. Th. Prior, F.G.S., has kindly aided the writer in 

 the critical examination of the rocks, and is communicating a 

 description of those of economic value to the forthcoming number of 

 the Mineralogical Magazine. They include niobates and titanates 

 of the rare earths, chemically allied to Euxenite and Fergnsonite, 

 Monazite containing Thoria, Cassiterite crystals of peculiar habit in 

 matrix, Corundum, and Scheelite. 



Our friend Mr. John Ballot, F.G.S., who knows Mr. S. Ryan and 

 the district very well, has favoured the writer with much information, 



' The specimens, labelled and numbered, are individually referred to as belonging 

 to the several divisions of the three great sections, X, T, Z, at the end of this paper, 

 ■with some unavoidable irregularity in the successional numbers. (See pp. Ho, Hi.) 



