V.—Contributions to South African Petrography

• Published in: Geological Magazine
• Main Author: Mennell, F. P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1902
• Subjects: Iceland
• Online Access: http://dx.doi.org/10.1017/s0016756800177167; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800177167

It is remarkable, considering the enormous development of igneous rocks in South Africa, that so little has been written concerning the features they present in the field or under the microscope. Right away from Cape Town into the tropics, plutonic masses, dykes, and lava-flows interrupt the continuity of the sedimentary deposits with astonishing frequency. Some of these rocks, like the Cape Town granite and dolerite, are probably of pre-Silurian age; others, like the Kimberley lavas, were erupted during the Secondary period: while others, again, like the dykes and lavas of the Zambesi Valley, are probably of late Tertiary or even geologically recent date, as evidenced by the numerous geysers and hot springs which represent the final phase of not long antecedent volcanic activity. They appear to bear the same relation to the volcanoes of Central Africa as the British Tertiary lavas do to those of Iceland.