Geological Structure of Southern Rhodesia. 823 



shown to be especially developed along the eastern border of 

 Matabeleland, and their conspicuous banding is attributed to re- 

 crystallization of fine mechanical sediments under pressure. 



The Conglomerate-beds (or Rhodesian ' Banket') are 10,000 feet 

 thick, and rest un conformably upon the ironstone series in the west, 

 both, these formations being gold-bearing. But they overlap also 

 elsewhere on to the ' basement series;' while they are represented 

 apparently in North Mashon aland by a thick series of grits, 

 resembling microscopically the Moine Gneisses of the Scottish 

 Highlands. The series contains pebbles of granite free from micro- 

 cline, and banded ironstones. 



The thick crystalline limestones overlying the conglomerate 

 series contain chert and dolomite, the latter rock occurring also as 

 an alteration-product from serpentine. Graphite also is found, and 

 is attributed to the insolubility of carbonaceous matter in a highly 

 siliceous magma. Contact-alterations of the limestones by the 

 granites are described. 



The granites occupy the greater part of the area dealt with, and 

 their intrusive character as regards the metamorphic rocks is shown. 

 The normal granites are biotite -bearing, and have microcline as the 

 dominant felspar; they never contain hornblende or muscovite. 

 Patches of micropegraatite are included in the microcline. proving 

 that the ' eutectic ' was not the final residuum of crystallization. 

 Orthite, as well as epidotc, occurs in most sections cut from the 

 Matopo Granite, and the author compares the mixed rocks of the 

 gneissose edges of the granite with the 'Fundamental Gneiss' of 

 Canada and other regions. 



The sedimentary series is subdivided as follows : — 



Zambesi Basin. TJiickness in feet. 



Taba's Induna Series 200 



Forest Sandstones and Basalts 1000 



E->eai*pmenl Grits 400 



Upper Matobola Beds (coal-bearing) 300 



Buse Beds (local only?) 300 



Lower Matobola Beds (coal-bearing) 200 



Sijarira Series 2000 



Li m pup o Basin. 



Tuli Lavas. 

 Guul Beds. 



Unconformity 



Samkoto Sandstones. 



No fossils are recorded, other than silicified wood, except in the 

 coal-bearing beds, in which occurs Palceomuteta keyserlingi of the 

 Russian Permian, as also plants. 



Various igneous rocks are described, including the great mass of 

 picrite extending nearly across Rhodesia, which the author con- 

 siders to be intrusive along a thrust-plane. 



The paper concludes with a description of the diamond-bearing 

 beds of Rhodesia, which resemble those of Kimberley, and also 

 contain fragments of eclogite. 



