162 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN [Vol. 8, No. 3 



PHYSICAL FEATURES AND GEOLOGY 



From the prominence of its mountains and lakes, Nyasaland has been called 

 the "Scotland of Africa" by an admirer of its scenic beauties. About 520 miles 

 in length and from 10 to 130 miles in width, it has an area of approximately 

 37,890 square miles. To the northwest is Northern Rhodesia, to the north and 

 northeast Tanganyika Territory, and bordering its southern half Mozambique or 

 Portuguese East Africa. 



To quote from Dixey (1932): "The dominant feature in the physiography 

 of the country is the deep, trough-like depression, forming part of the Great 

 Rift Valley, that traverses it from end to end; the greater part of this trough 

 is occupied by Lake Nyasa and the remaining part by the Shire River. The 

 country on either side of the trough is made up of high plateaux. For example, 

 that lying west of the lake stands mainly between 3,300 and 4,400 feet above sea- 

 level. Near Dedza it rises to about 5,000 feet and towards the northern end of 

 the lake the Vipya, Nyika, Mafingi and Misuku uplands rise to altitudes of 6,000 

 to 7,500 or even 8,000 feet. South of the lake the Shire Highlands plateau is sur- 

 mounted by the Mlanje Mountains, rising to nearly 10^,000 feet, and the Zomba up- 

 lands to about 7,000 feet. 



"Lake Nyasa stands at an elevation of about 1,520 feet, and the adjacent 

 lake plains rise to about 1,700 feet; the southern part of the rift, occupied by 

 the Lower Shire, stands only at 200 to 300 feet above sea-level. 



"Owing to the manner in which it is traversed by the rift valley a large 

 proportion of the Protectorate is more or less of mountainous character; this is 

 particularly the case along the sides of the rift valley, which are generally steep 

 locally and even precipitous. Apart from the floor of the Upper and the Lower 

 Shire Valley, almost the only country of fairly even surface comparable with the 

 greater part of Southern and Northern Rhodesia is the Angoniland plateau, which 

 indeed is merely an extension of the great Rhodesian plateau. " 



Lake Nyasa, the third largest lake in Africa, is 350 miles long, 20 to 50 miles 

 wide, and near its northern end over 300 fathoms deep. Smaller lakes include 

 Lake Chiuta and shallow, brackish Lake Chilwa on the eastern Portuguese border. 

 Lake Chilwa has no outlet. 



With the exception of an area on the eastern Portuguese border which drains 

 in part east to the Lujenda River and in part to Lake Chilwa, the whole of Nyasa- 

 land is drained by streams that flow to the Rift and empty into either Lake Nyasa 

 or its outlet the Shire River, and so, by the Shire, south to the Zambezi. The long- 

 est river other than the Shire, the South Rukuru, has a length of about 170 miles. 

 Many of the rivers run throughout the year in their upper course, but are intermit- 

 tent in their lower course through evaporation and absorption in the dry season. 

 Only a few maintain a year-round flow throughout their entire length. 



Dixey (I.e.) states that the basement rocks of Nyasaland consist of a complex 

 of schists and gneisses, probably Pre-Cambrian, invaded by various intrusives. 

 Massive intrusions of syenite, well exemplified in Mlanje and Zomba mountains, 

 constitute prominent orographical features. Isolated blocks of sediments and 

 lavas of the Karroo System (Permain to Rhaetic) occur as relicts of denudation, 

 preserved by down-faulting into the older rocks in the Lower Shire Valley, on 



Explanation of map on page 163 



Map of Nyasaland showing routes and principal collecting localities of the Vernay 

 Nyasaland Expedition. 1. Blantyre, Shire Highlands. 2. Zomba Plateau. 3. Likubula 

 Gorge. 4. Luchenya Plateau, Mlanje Mountain. 5. Nchisi. 6. Nyika Plateau. 7. Kasungu. 

 8. Camp Chibotela, Chia area. 9. Cholo Mountain. 10. Chikwawa. 



