TRANSACTIONS OF SECTION E. 623 



paper the author concludes that we have here beds representing, not a con- 

 tinuous sequence, but a series of episodes in the Tertiary history of the country. 



The geography is, of course, directly related to the lithology and the geo- 

 logical history of the rocks. Four distinct types of country have to be studied : 

 the first is that built up of complexes of crystalline rock ; the second, that formed 

 by the Cretaceous strata; the third, composed of Tertiary beds, the most con- 

 spicuous of which are the red sandy clays typical of Ijebu and Benin ; the fourth, 

 still in process of formation, of the delta and mangrove swamps. Each of these 

 exhibits physical features peculiar to itself and not shared by any other member of 

 the series. 



Brief reference is made to the salient characteristics of each group. In the 

 Oban Hills we find an unorientated group of peaks, attaining an elevation of 

 rather over 3,000 feet, characterised by steep slopes and drained by a rejuvenated 

 river system. The best example known to the author of the second type of 

 scenery is that between Afikpo and Abakalliki, where the effects of erosion on a 

 group of strata of varying hardness, folded by a north and south movement, are 

 admirably seen. This is an open country of the orchard type, most assiduously 

 cultivated, but on the northern and southern slopes of the Oban Hills the Cre- 

 taceous rocks are covered with dense bush, which masks the physical features. The 

 country formed by the softer red loams and sands characteristic of parts of the 

 central and western provinces is exceedingly monotonous, covered with heavy bush 

 and drained by a very mature river system. 



The watercourses are greatly encumbered by sandbanks. Near Asaba we find 

 low hills, but for the most part, e.g., between Ifon and Sapele, the surface is gently 

 undulating. In regard to the delta region, probably in reality this is not as flat 

 as it appears from the sea, for inliers of the red sands of Benin, forming low hills 

 and surrounded by mangrove swamps, are not uncommon. 



Tlie Visit of the British Association to South Africa. 

 By H. Yule Oldham, M.A. 



MONDA Y, A UQ VST 6. 

 The following Papers and Reports were read : — 



1. Geographical Photography. By John Thomson. 



Report on Investigations in the Indian Ocean. 

 See Reports, p. 331. 



3. The Percy Sladen Expedition in H.M.S. ' Sealark ' : The Chagos 

 Archipelago. By J. Stanley Gardiner. 



The Chagos Archipelago is perhaps the least known coral region in the world. 

 Situated nearly 6° to the south of the Maldives, from which it is separated by over 

 2,000 fathoms of water, its bank within the 1,000-fathom line covers about 21,000 

 square miles. In this area arise a series of shallower banks, separated by 300 to 

 800 fathoms of water, varying from approximately flat submerged shoals at 20 

 fathoms or less to large, more or less complete, ring-shaped surface reefs, or atolls. 

 The whole is probably part of a large land mass which connected Madagascar to 

 Southern India up to the commencement of the Tertiary period (Eocene). The 

 submerged banks are believed to be gradually assuming the atoll-shape by coral 

 and algal (nullipore) growth on their edges. If the existing atolls have been 



