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



the Angoniland plateau, and near the/ northwestern shores of Lake Nyasa. The 

 Karroo beds of the north have been found to contain a rich vertebrate fauna. 

 Dinosaur beds of probable early Cretaceous age occur within the Rift Valley to 

 the northwest of Lake Nyasa. A series of lacustrine and fluviatile beds along 

 the northwestern shores of Lake Nyasa throws much light on the earlier history 

 of the lake. The oldest of these beds may possibly date back into the Tertiary. 

 Succeeding beds have yielded a number of mammalian remains (mastodon, ele- 

 phant, hippopotamus, giraffe) which together indicate an early or possibly middle 

 Pleistocene age for these beds. 



The earlier crustal movements which resulted in the step*faultings responsible 

 for the Nyasaland part of the Great Rift are considered to have taken place in 

 pre-Pliocene, probably Oligocene, times. The movements have continued inter- 

 mittently and have not yet come to an end. Volcanic activity associated with the 

 rift-forming movements has ceased in Nyasaland, although hot springs occur, 

 usually on lines of fracture belonging to the rift valley system of faults. 



CLIMATE 



Dixey (1932) has given a resume of the palaeoclimate of Nyasaland as re- 

 vealed by study of the rock formations. The glacial conditions under which the 

 earlier Karroo strata were laid down in more southerly parts of Africa apparently 

 did not extend to Nyasaland. After the cold conditions there was a warmer phase 

 which led to the growth of a luxuriant vegetation and the deposition of coal- 

 bearing strata in our area. Toward the end of the Karroo period the climate be- 

 came increasingly drier and warmer until finally desert conditions existed over 

 the whole of Nyasaland in common with the greater part of Africa. In Dinosaur 

 times, moister conditions again returned. Within Tertiary and post-Tertiary times 

 several major alternations from drier to wetter conditions took place. There is 

 evidence for the correlation of certain of the wetter periods -with the Pleistocene 

 glacial period of Europe, the colder phases of which were probably represented in 

 our area by greatly increased humidity. One period in the Lake Nyasa sequence 

 of lacustrine beds, indicated by recession of the lake and the accumulation of 

 fine red sands, may possibly correspond to the Rhodesian desert period, during 

 which the Kalahari sands were laid down. 



The present-day climate of Nyasaland is characterized by and large by al- 

 ternating wet and dry seasons, with abundant rainfall in summer and scanty rains, 

 and in some areas no rain at all, in the cooler months. The rainy season generally 

 begin s*about the end of November and continues to about the end of March. Janu- 

 ary and February are generally the wettest months and May through September al- 

 most equal in dearth of rain. In the northern part of the country the wet season be- 

 gins a little earlier and ends about a month later than in the south. On the higher 

 mountains, and on adjacent parts of the elevated plateaux on either side of the 

 Rift Valley, the southeast trade winds bring spells of mist and cold rain, called 

 "chiperoni," from which there is often appreciable precipitation in the winter 

 months. 



As might be expected in an area of such diverse topography and differentia- 

 tion in elevation of the land -surface, rainfall varies greatly. The annual fall ranges 

 from an average of about 25 to 30 inches in the Lower Shire Valley, which is the 

 driest part of the Protectorate, to about 110 inches recorded at an altitude of 

 about 6,000 feet on Mlanje Mountain, where there is no very pronounced dry season. 



Temperature and atmospheric humidity likewise vary greatly in relation to alti- 

 tude and other controlling factors, and, like the rainfall, temperatures vary con- 

 siderably in different years. The hottest time of the year is in November, before 



