Vol. 6^.~] GEOLOGY OF THE ZAMBEZI BASIN. 163 



these traverses being over 2000 square miles. In exploration of this 

 kind, through dime alt country, where the exigencies of the daily 

 march are ever insistent, it is of course rarely practicable to follow 

 up the evidence that presents itself. One must usually be content to 

 snatch just so much as lies in one's path ; therefore it is inevitable 

 that the facts which come under observation will frequently be of 

 less consequence than those which remain undiscovered. In my 

 attempt in the following pages to give coherence to the collected 

 data, I am aware that some of the conclusions rest upon an imper- 

 fect basis ; but it may be long before fuller knowledge is accumulated, 

 and meanwhile it seems desirable that what we already possess be 

 used so far as may be in temporarily bridging the gaps. 



The most serious difficulty in work of this kind arises from the 

 absence of a topographical map upon which to record the geological 

 observations. In the present case, some parts of our route appear 

 not to have been previously traversed by the white man, while 

 for the other parts the existing maps are too inaccurate to be of 

 much service ; and I unfortunately found it impossible, under the 

 conditions of our journey, to construct a map adequate to supply 

 the deficiency. In plotting the imperfect sketch-map that accom- 

 panies this paper, I have had to rely largely upon compass-bearings 

 and dead reckoning, taking as a basis the plan of the railway. 



The country which I personally examined, and shall now more 

 particularly describe, extends from near the Victoria Palls east- 

 ward for about 75 miles to the confluence of the Zambezi with 

 its tributary the Deka, and from the plateau north of the Zambezi 

 southward for about 70 miles to the head- waters of the Deka. 



II. Peevious Literatuee. 



Until recently our knowledge of the geology of this part of 

 Rhodesia depended upon the casual notes of a few travellers, of 

 whom David Livingstone was first and foremost. In his eastward 

 march from the Victoria Palls in 1855, and in his later journeys of 

 1860, Livingstone went to the northward of the country now to be 

 described ; but at one place he turned southward to visit the great 

 Moamba [Mamba] cataracts of the Zambezi within its gorge ; and 

 at this spot only did our expedition touch the track of the great 

 explorer. His record of these journeys includes some notes on the 

 rocks of the Batoka Highlands, 1 which are still, so far as I am 

 aware, the only published information on the geology of that 

 district (see p. 171). 



The best account, even to the present day, of the more frequently 

 traversed country south of the Zambezi is that given by James 

 Chapman in 1868. Though not pretending to technical knowledge, 

 Chapman had an observant eye for the rocks ; and much geological 



1 ' Missionary Travels & Researches in South Africa ' (London, 1857) 

 chap, xxvi, p. 534 & chap, xxvii, pp. 542-43 ; and ' Narrative of an Expedition to 

 the Zambesi & its Tributaries' (London, 1865) chap, xi, pp. 222-23. 



