200 R. R. Walls — The Geology of Portuguese Nyasaland. 



sented by the few feet of variegated marls which there rest non- 

 sequentially upon Aptian clay and are overlain by red and mottled 

 Lower Chalk. 



In view of recent detailed work on the Albian zones, we should 

 perhaps remark that in the foregoing pages we have used the terms 

 " interruptus- zone " and " rostrahcs-zone'' in the general sense of 

 existing stratigraphical classifications. As regards the lowest beds 

 of the Gault at Black Ven (previously assigned by some authors to 

 the interruptus- zone), Dr. W. D. Lang has informed us, since the 

 first part of this paper appeared, that he has obtained ammonites 

 from those beds (his beds 1, 2, and 3) and that Dr. L. F. Spath 

 has pronounced them to be Upper Gault forms. 



The Geology of Portuguese Nyasaland. 



By Egbert E. Walls, M.A., B.Sc. 

 (WITH PLATES VII AND VIII.) 



pOETUGUESE NYASALAND is the name given to the most 

 -*- northern part of Portuguese East Africa, lying between Lake 

 Nyasa and the Lidian Ocean. It is separated from the Tanganyika 

 territory in the north by the Eiver Eovuma and from the Portuguese 

 province of Mozambique in the south by the Eiver Lurio. 

 The territory measures about 400 miles from east to west and 

 200 miles from north to south and has an area of nearly 90,000 square 

 miles. This territory is now perhaps the least known part of the 

 once Dark Continent, but while the writer was actually engaged in 

 the exploration of this country in 1920-1, the Naval Intelligence 

 Division of the British Admiralty published two handbooks, the 

 Manual of Portiiguese East Africa and the Handbook of Portuguese 

 Nyasaland, which with their extensive bibliographies contained 

 jDractically everything that was known of that country up to that 

 date (1920). These handbooks make it unnecessary in this paper to 

 give detailed accounts of the work of previous explorers. 



The geological information is meagre, and is obtained chiefly from 

 the reports of Livingstone (1862-6), Thomson (1881), and Huddart 

 (1906). Practically all the more important expeditions into ihis- 

 territor}- have been made via the Eiver Eovuma and its tributary, 

 the Lujenda in the north, or from Lake Nyasa in the west, and the 

 south-eastern parts have been entirely neglected. It was in the south- 

 eastern part that the writer did most of his explorations, so that the 

 whole territory has now been at least roughly surveyed. Generally 

 speaking, the country rises from the level plains along the coast to 

 high mountainous land near Lake Nyasa. Several large rivers are 

 shown on the map rising in the mountainous interior and draining 

 into the Indian ocean, but only two of these rivers, the Eovuma, 

 with its tributary the Lujenda, in the north, and the Lario in the 

 south, contain running water all the year round. The outstanding 

 feature of the country is its dryness, large stretches being practically 



