August 16, 1907] 



SCIENCE 



227 



so that a widening area of sharply dissected 

 country, very difficult to traverse, extends east- 

 ward from the falls, on each side of the main 

 gorge. Some 300 miles east of the falls, the 

 Kafue river, coming from the north, flows in a 

 broad shallow valley for several hundred miles 

 across the undulating plateau country, then 

 plunges down through a succession of cata- 

 racts in a rugged gorge, descending 1,000 feet 

 in two miles, after which it has a sluggish 

 course of 20 miles to its confluence with the 

 Zambesi. 



The systematic manner in which the forms 

 appropriate to old age on the plateau are re- 

 placed by those appropriate to youth in the 

 gorge and its branches gives new warrant — if 

 any new warrant is needed — for the use of a 

 systematic terminology in the explanatory 

 description of land forms. The structure of 

 the region being stated in the first place, it 

 suffices to say that the old features of the 

 plateau are replaced by young features of 

 strong relief Lelow the falls ; all the more 

 characteristic forms may then be easily in- 

 ferred. The space saved by the adoption of 

 this concise style of description may then be 

 used to advantage for accounts of individual 

 features. For the highland area, " shallow 

 valley," " shallow trough " and " channel sunk 

 very slightly below the general level of the 

 plateau " are the paraphrases which Lam- 

 plugh uses instead of the systematic term, 

 "old valley"; the fact that thiee different 

 descriptive phrases are thus used in a single 

 article for one and the same class of forms 

 only emphasizes the need of the adoption of a 

 single, definite, technical term. 



A PENEPLAIN IN SOUTH AFRICA 



During the excursion of the British Associa- 

 tion to South Africa in 1905, the undersigned 

 had opportunity of traversing the High Veld 

 of the interior on several different lines, and 

 thus of gaining a general impression of its 

 leading features (see " Observations in South 

 Africa." Bull. Geol. Soc. Amer., XVII., 

 1906, 377-450). As to structure, the region is 

 broadly covered with a heavy series of nearly 

 horizontal Mesozoic continental formations, 

 resting unconformably on a complicated series 



of much older rocks, which appear to have 

 been reduced in pre-Mesozoic time to the state 

 of subdued mountains or hills, and which have 

 since suffered still further reduction in the 

 long continued cycle of erosion by which a 

 vast body of material has been swept away. 

 The present nearly-level highland of the tree- 

 less plains bevels across the Mesozoic strata at 

 very gentle angles, and except for the scat- 

 tered strong reliefs in the form of stony ridges 

 and mesas maintained by resistant dolerite 

 dikes and sheets, the surface has truly reached 

 an expression of penultimate erosion. The 

 low swells between the water courses have a 

 thin soil; they are often of very faint con- 

 vexity, nicely indicated by the faint arching 

 of the long railway tangents. The water 

 courses, unlike the broad and ill-defined wadies 

 in the peneplain in equatorial Africa described 

 in Science for August 2, 1907, are deep, well- 

 defined channels, bordered by 20 or 30 feet of 

 alluvium which cloaks the wide-open old-valley 

 floors. The channels were nearly dry at the 

 time of our visit, but bore the marks of having 

 carried heavy floods in previous wet seasons 

 (southern siunmer) when heavy local down' 

 pours occur. A curious minor item was the 

 occurrence of rapids in the dwindled streams 

 of the dry season, where rock sills occurred 

 in the deep channel beds : this at first sug' 

 gested a recent revival of erosion; but it was 

 afterwards better understood that the long 

 established grade of these old drainage lines is 

 indicated by the even slope of their alluvial 

 flood-levels and not by the small inequalities 

 in their flood-scoured beds. Where the water 

 courses lead through notches in the dolerite 

 ridges, the channels are encumbered with 

 boulders and their fall is more rapid than else 

 where; thus the Veld is divided into compart- 

 ments of slightly different altitudes. 



The Veld stands at altitudes of from 6,000 

 to 8,000 feet, with a gentle slope to the west, 

 which turns a large drainage area to the 

 Orange Eiver system. The eastern border of 

 the Veld is suffering invasion by the head 

 ravines of actively retrogressive streams that 

 descend rapidly to the coastal lowlands of the 

 Indian ocean; and this feature, along with 

 certain other indications, led to the belief that 



