202 MK. G. W. LAMPLTJGH ON THE [May 1907, 



it must have been transported into this region from without. 

 Curiously enough, I saw comparatively little surface-sand in the 

 sandstone -country around "Wankie, where there is an immediate 

 source for the material ; but this district is so much dissected that 

 loose detritus is likely to find its way rapidly into the stream-beds, 

 whence it will be transported out of the sandstone-country to the 

 Deka, and thence to the Zambezi. 



Dr. Passarge considers that the river-transport of the sands was 

 mainly effected during a ' Pluvialzeit ' which was contemporaneous 

 with the Glacial Period of our latitudes, and that their rearrange- 

 ment took place during an ' Interpluvialzeit/ 1 Into these specu- 

 lations I shall not venture to enter further than to state my 

 impression that, whatever their earlier history may have been, the 

 sands bordering the Batoka Gorge have reached their present 

 position during a period of greater aridity and stronger winds 2 than 

 now obtain in this region ; and that there has since been a time 

 (?the Glacial Period) of much greater rainfall than the present, 

 during which the sands became fixed, clad with vegetation, and in 

 places deeply eroded by streams which have now disappeared. 



The reader who desires fuller information should peruse Dr. 

 Passarge's great work, in which the Kalahari Sands, together with 

 the other superficial deposits, are fully discussed in all their aspects. 



Surface-Limestone and Tufa. 



In the region traversed, calcareous deposits due to the evaporation 

 of lime-charged waters are of common occurrence, but are usually 

 of very limited extent and of recent origin. Owing to the interest 

 excited in all the superficial deposits by Dr. Passarge's work, a short 

 description of those which I observed seems, however, desirable. 



Surface-incrustations of this character border many of the dry 

 stream-courses and shallow vleys, reminding me of a similar crust 

 or ' caliche ' which I have seen under like conditions in Arizona. 



In the Batoka Gorge the great cliffs of basalt are frequently 

 streaked vertically with greyish-white incrustations, due to lime 

 and other minerals deposited by water oozing from small springs 

 and evaporating in the torrid air of the chasm (see, for example, 

 PL XI). These markings are frequently strung along a definite 

 bedding-plane, but at the time of our visit all these places appeared 

 to be absolutely dry. Indeed, I was everywhere impressed with 

 the rarity or absence of true rock-springs, seeing that the strongly- 

 jointed structure of the basalt and the deep trenching of the 

 country by the gorges appeared to afford most favourable con- 

 ditions for them. The springs that I saw were all due to the slow 

 oozing of water from the loamy fiats, except a single one which I 



1 f Die Kalahari ' 1904, chap, xxxvii. 



2 I am informed by Mr. E. T. Coryndon that, in Northern Ehodesia, the 

 winds at the present day are never strong enough to drift these sands, even if 

 they were not sheltered by vegetation. I take this opportunity of also acknow- 

 ledging my indebtedness to Mr. Coryndon for many useful items of information 

 regarding the structure of the country beyond my traverse north of the 

 Zambezi. 



