ii 4 



NA TURE 



[November 30, 1905 



in the backward race. The narrowness of the canon below 

 the falls, as compared with the breadth of the river above 

 them, shows that only by such concentration has the 

 Zambesi been enabled to tear out its gorge so far back into 

 (he plateau. 



Mr. Molyneux has rightly laid stress on the behaviour 

 of the tributaries as proof of the erosive origin of the 

 Batoka Gorge. Above the Falls the tributaries have so 

 nearly reached their base-level relatively to the Zambesi 

 that they hold deep back-waters where they join the main 

 river, of which the Maramba, 2 miles from the Falls, 

 presents a good example. But below the Falls they 

 have at first been left in shallow open " hanging 

 valleys," high above the main artery; and thus rejuven- 

 ated by a sheer drop of 350 feet or 400 feet, each little 

 stream has begun to work vigi rously backward into the 



-Katonga's Cleft 



ph by Mr. F. W, Sykes. 

 The walls are about 300 



plateau along its own line of drainage. Each waterfall 

 tends to recede farther and farther within its mvn pre- 

 cipitous rift as we followed the Zambesi downward, so that 

 while at first it was possible to round the heads of these 

 by a detour of a few hundred yards, we found that 

 farther east not only do they extend far back into the 

 plateau, but many minor clefts branch out from them, 

 rendering tin country a maze of dangerous chasms. In 

 these waterfalls and rifts the salient features of the 

 main gorge are often reproduced in miniature. The 

 most remarkable example that we visited occurs on the 

 Karamba, a stream which joins the Zambesi about 35 miles 

 east of the Falls. Some 5 miles above its junction with 

 the Zambesi this stream drops by a waterfall from its 

 open shallow valley into a gloomy recess, from which it 

 escapes bj swerving at a right angle between nearly 

 vertical rock-walls, 300 feet in height, through a cleft 

 only 15 feet to 20 feet in breadth (Fig. 2). 



NO. 1883, VOL. 73] 



If further proof for the erosive origin of the Batoka 

 Gorge be needed, I would direct attention to the gradual 

 falling off in the angle of slope of its sides as we descend 

 the river. At the Falls, where the gorge is freshly cut, its 

 walls are practically vertical ; but a few hundred yards 

 below they are already beginning to show the effect of 

 weathering by a slight recession of their crest-line and 

 by indications of terracing along the planes of stratification. 

 At the Songwe confluence, 7 miles farther down, this re- 

 cession and terracing have become so pronounced that the 

 average angle of slope from base to crest is reduced to 

 6o° or less ; at the Tshimamba, about 30 miles below the 

 Falls, it is no more than 35 ; and at the mouth of the 

 Karamba, 12 miles farther east, the sides of the gorge 

 have been weathered down into bushy slopes, broken here 

 and there by inconspicuous bars of crag, with an average 

 inclination of about 30°, which is also the character of the 

 canon at the place where it was visited still farther east- 

 ward. 



If time:' had permitted, I should have- liked to discuss 

 the curious difference between the broad basin of the 

 Matetsi and the narrow trough of the Zambesi within the 

 basaltic plateau, which presents an important problem in 

 the physiography of the region, especially when we re- 

 member that the Batoka Gorge terminates at a short 

 distance above the confluence of the Matetsi ; but this 

 would open up too wide a subject for the present occasion. 



In the face of all the evidence we must conclude — 

 not without a tinge of regret — that the Batoka Gorge can 

 no longer be allowed to stand apart, a unique curiosity, 

 among the valleys of the earth — that no exceptional forces 

 have been brought into action to produce its wonders and 

 its loveliness — but that the everyday effects of river and 

 rain, with time — that indispensable factor to the geologist 

 — a very long time — are ample to explain all its marvels, 

 as they have already explained the marvels of many another 

 noble canon of the world. 



I must not let pass this opportunity of express- 

 ing my gratitude for the kindness shown to me by 

 the officers of the British South Africa Company in 

 Rhodesia and also in London, by the engineers of the 

 Wankie Coal Mine and of the Rhodesia railways, and 

 by many other friends in Rhodesia. To Mr. F. W. Sykes 

 I am peculiarly indebted for removing difficulties that, 

 except for his self-sacrificing cooperation, might have 

 Droved insuperable. G. W. L. 



INDIAN DEEP-SEA HOLOTHURIANS. 1 

 'T'HE most recent addition to the list of publications 

 issued by the Indian Museum, Calcutta, deals with 

 a collection of deep-sea Holothurians made by the survey 

 ship Investigator, which has rendered valuable service in 

 the interests of deep-sea research. The extreme utility of 

 this work, which will help to elucidate many of the 

 problems connected with deep-sea life, is enhanced by the 

 fact that the investigations have been carried on over 

 comparatively unknown ground, so far as the great depths 

 are concerned. 



The area examined by the Investigator is a comparatively 

 wide one, and ranges over the northern part of the Indian 

 < >c can from the Persian Gulf to the east side of the Bay 

 of Bengal. 



Most of the deep-sea expeditions appear to have confined 

 their labours to the Atlantic and Pacific Oceans, and even 

 the Challenger did not touch the northern part of the 

 Indian Ocean. The Siboga Expedition reached the extreme 

 south-eastern portion of the Investigator area, and a com- 

 parison of the Siboga Holothurians with those in the 

 paper under notice provides an interesting study, and, in- 

 cidentally, confirms the opinion that a knowledge of the 

 distribution of deep-sea forms derived from an examination 

 of isolated areas is apt to be misleading. 



Of the seventy-five species and varieties described in the 

 report, no less than sixty are new to science. The 

 Synallactids appear to be the predominant forms amongst 

 the deep-sea Holothurians of the Indo-Pacific region, both 



Indi: 



'An Ac 

 Mari 



of the Deep-sea Holothurioidea collected by the Roya 

 urvey Ship Investigator" By R. Kcehlsr and C. Vaney 

 5. (Indian Museum, Calcutta, 1905.) 



