Vol. 63. J GEOLOGY OF THE ZAMBEZI BASIN. 195 



' Chenamba Hills ' 1 — which Dr. Passarge considers to be probably 

 indicative of the re-emergence of the basalts ; but the position as well 

 as the geology of these hills is uncertain. At the farther side of the 

 desert south-westward, Dr. Passarge found the ancient gneissose and 

 schistose rocks exposed in the neighbourhood of Lake jSTgami ; but 

 if he is right in correlating the amygdaloids (' Loalemandelstein ') 

 which emerge at the eastern fringe of the desert in the Palapye 

 district with the Batoka Basalts, it seems possible that a considerable 

 portion of the Kalahari between the Zambezi, the Chobe, and the 

 Makarikari Saltpans may be underlain by these rocks. The basis 

 for this speculation is however so slender, that it is not worth further 

 discussion. 



Without extending the hypothetical boundaries far into either 

 the western or the southern desert, we obtain an area of over 20,000 

 square miles as the approximate extent of the Batoka Basalts on 

 a conservative estimate, and it may be very much more. But in 

 any case the area of these old lava-fields cannot nearly attain the 

 magnitude of the Deccan Traps of India or of the Snake-River 

 Basalts of Western America. 



Thickness of the Basalts. 



As will be understood from the foregoing description, I found no 

 means of ascertaining the thickness of the Batoka Basalts. It must 

 in places exceed 1000 feet, as I saw nearly this thickness in a 

 single section, in descending from the plateau south of the Zambezi 

 to the bottom of the gorge approximately opposite the con- 

 fluence of the Namaruba River; and at this spot presumably 

 a very considerable mass had been removed from the top in the 

 development of the plateau, and the base was still not exposed. 

 What the thickness of the lava-fields in their deepest part 

 may originally have been, must, I think, from the nature of the 

 country, always remain a matter of conjecture. 



Age of the Basalts. 



Two views have been expressed respecting the geological age of 

 the Batoka Basalts, but the evidence for either is at present slender. 

 Mr. A. J. C. Molyneux," 2 whose opinion is endorsed by Mr. F. P. 

 Mennell, considers them, as already mentioned (p. 184), to be 

 probably contemporaneous with the similar basalts interstratified 

 with the ' Forest Sandstones ' of the country which he examined, 

 farther eastward. In the absence of palaeontological evidence, the 

 age of the ' Forest Sandstones ' is left uncertain by Mr. Molyneux ; 

 but Mr. Mennell considers them to be probably Tertiary, basing his 

 argument chiefly upon the supposed recency of volcanic activity in 



i ' Travels in the Interior of South Africa ' vol. i (1868) pp. 150, 161, & 

 277-78. 



2 'The Sedimentary Deposits of Southern Rhodesia* Quart. Journ. Geol. 

 Soc. vol. lix (1903) passim. 



