Vol. 63.~] 'GEOLOGY OF THE ZAMBEZI BASIN. 183 



At the Victoria Falls, the section in The Chasm reveals at least 

 four massive beds, in thickness ranging from 40 feet to 80 or 

 100 feet, with intercalated breccias which show lateral variation in 

 thickness from a few feet to 30 feet. It was observed, in excavating 

 one of these breccias for the foundation of the railway -bridge on the 

 western side of the gorge, that the rock though hard at the surface 

 was comparatively soft within, the surface-induration being no 

 doubt caused by mineral deposition from evaporating moisture — a 

 condition of common occurrence throughout the region, especially 

 in the more porous rocks. 



The Breccias. 



The breccias, which are usually red or pale ashy-green, vary 

 greatly in texture as well as in thickness, swelling out occasionally 

 into huge bosses of coarse agglomerate, in which some of the 

 masses are vesicular and ' bomb '-like. I kept in mind the possi- 

 bility that some of these might indicate the position of eruptive 

 vents or ' necks,' but failed to detect any instance where this origin 

 could be proved. In the bottom of the gorge at the confluence of 

 the Songwi, 6 or 7 miles below the Victoria Falls, a thick mass of 

 breccia, composed in part of huge angular blocks, was well exposed 

 on the flood-platform of the river, and rose up at one place in crags 

 over 30 feet high. This, at first sight, suggested a small vent ; but 

 the mass could be traced as a definite band in the adjacent cliff, and 

 was there underlain by the sheet of dense basalt which extended 

 across the floor of the gorge ; and there was no sign that this basalt 

 was anywhere pierced by the breccia. The absence of any other than 

 basaltic fragments from all the breccias that I examined also tells 

 against the probability of any of the breccias being truly eruptive. 



At two or three places while traversing the plateau, especially in 

 the broken country immediately east of our route after crossing the 

 Kalomo Eiver, we passed over areas in which the basalts lost for a 

 space their usual tier-like aspect and became tilted, confused, and 

 irregular, leading me temporarily to anticipate that we were 

 approaching an eruptive focus ; and it is, of course, possible that in 

 these places we may have traversed the outskirts of a volcanic centre 

 without making a near approach to it. 



From previous information I had expected to find red sandstone 

 interbedded with the basalts in the gorge below the Falls ; but all 

 the red beds that I could reach proved to be stained breccias and 

 not sandstones. As already mentioned, my search for interbedded 

 sediments was fruitless throughout the district ; but this does not 

 preclude the possibility of their occurrence beyond the area examined. 

 Indeed, I saw from the train, in the Katuna valley (between Deka 

 Bridge and Matetsi), some greenish-grey and reddish beds of shaly 

 aspect among the basalts, unlike any rocks that I had the oppor- 

 tunity of examining at close quarters. As the massive rocks also 

 show much irregularity and variability in this neighbourhood, its 



