yd. 63.^ geology of the zambezi basin. 215 



Discussion. 



The President, in returning the thanks of the Society for the 

 interesting and luminous contribution to our knowledge of African 

 geology and physiography made by the Author of the paper, referred 

 to the earliest information regarding the region which was obtained 

 by Livingstone, and to the prevalent opinion at the time that the 

 striking gorge of the Zambezi is due to a vast rent in the crust of 

 the earth. It was satisfactory to him to find the suggestion con- 

 firmed which he then made, nearly half a century ago, that even 

 the ravine of this African river is no exception to the rule that 

 such topographical features are due to river-erosion. The details 

 furnished by the Author from his own personal survey of the ground 

 were of great value, in showing how rock-structures had modified 

 the progress of the erosion and would give rise to future important 

 changes in the course of the river and the excavation of its caiion. 

 The similarity of geological conditions and of the resultant topo- 

 graphy between the basalt-plateau and gorge of the Zambezi, and the 

 lava-fields and canons of the Snake River in Western America, was 

 remarkable. If the Author had succeeded, during his short sojourn 

 in the country, in gleaning such an amount of new and important 

 facts, it was to be expected that a still ampler harvest awaited more 

 prolonged and exhaustive investigation. As a piece of pioneer-work, 

 his paper was an admirable example of how much could be achieved 

 in a short time by a trained eye and an experienced judgment. 

 It would form a memorable feature in the history of African geo- 

 logical exploration, and meantime was heartily appreciated by the 

 Society. 



Dr. Hatch said that, during his visit to Rhodesia in 1894, he did 

 not get as far north as the Zambezi River, and therefore he could 

 not speak from any personal knowledge of the district so admirably 

 described by the Author ; but he had made some study of the 

 volcanic rocks of other parts of South Africa, and the Author's 

 paper appeared to the speaker to have an important bearing upon 

 these. His description of the Batoka Basalts, especially of the 

 amygdaloidal bands that occur in the upper part of the flows, with 

 their vesicular cavities infilled with agate, green-coated chalcedony, 

 quartz, and zeolites, recalled exactly the character of the Bushveld 

 Amygdaloid, which covers a large area of the Transvaal immediately 

 north of Pretoria, namely, the well-known Springbok Flats. The work 

 of the Transvaal Geological Survey had shown that these lavas overlie 

 sandstones which are considered to be of Karroo age and younger 

 than the Permo-Carboniferous coal-measures of the Transvaal. 

 The Author stated that the Batoka Basalts are younger than the 

 Wankie coal-measures or Matobola Beds, which Mr. Molyneux 

 also considered to be of Permo-Carboniferous age. Again, there 

 was a remarkable resemblance in petrographical habit between the 

 Bushveld Amygdaloid and the lavas of the Volcanic Group of the 

 Drakensberg and the Malutiberg, especially in the occurrence of 

 the long drawn-out vesicles which had originated the name of 



