Vol. 63. j STRATIGRAPHY OF SOUTHERN NIGERIA. 309 



There can be do doubt that the deposition of the Benin Sands 

 took place during a very pronounced movement of subsidence 

 involving nearly all the southern half of the colony, while from 

 the succeeding movement of elevation many of the most prominent 

 features of the physiography must date. 



Underlying the Benin and Calabar Sands we find a series of clays 

 or shales alternating with sandy strata. These have been studied 

 in two localities : the first at Asaba and the neighbourhood, where 

 I have applied to the beds the term the Lignite Series, from the 

 occurrence in them of that material. The second in the Ijebu 

 district (Lagos Province), about 140 miles to the west-north-west : 

 these I term the Ij ebu Series. They are characterized by con- 

 taining impregnations of bitumen. 



The relations of these two sets of beds, one to the other and to the 

 Cretaceous Series below (most typically developed in the Eastern 

 Province), is unfortunately not at present known. 



Between the Benin Sands and the Lignite Series there is 

 certainly an unconformity, 1 and I feel little doubt that a minor 

 unconformity exists between the Benin Sands and the Ijebu Beds. 

 The difference in age of these two series is probably not great, and, 

 judging by the lesser degree of consolidation and the appreciably- 

 lower dip, I consider both distinctly younger than the Cretaceous. 

 In the present state of our knowledge it is impossible to assign any 

 definite thickness to either. 



It is interesting to record that no dykes or evidences of contem- 

 poraneous volcanic action have been found in these beds ; but, in the 

 Cross-Kiver basin (Eastern Division), dykes are of common occurrence 

 cutting Cretaceous strata. 



Four districts in Southern Nigeria have been visited by me, and 

 their principal geological features may be summarized as follows : — 



(a) The Central Province. 

 Here an extensive basement-platform of gneiss and schists is 

 overlain, as to its southern half, by the uniform expanse of the 

 Benin Sands. Erom the occasional appearance beneath the latter 

 of shales and sandstones, as, for example, near and to the north of 

 Benin City and near Ifon, I think it probable that we have here 

 representatives of the Ijebu Beds of the Lagos Province. Without 

 the advantage of boring-appliances these beds would have remained 

 almost unknown in their typical district; a comparison of these 

 adjacent localities shows that the mode of occurrence and the 

 degree of consolidation of the two sets of beds which crop out 

 below the Benin Sands are all but identical. 



(b) The Asaba District. 



At Asaba, and westward as far as the towns of Ibusa and Okpa- 

 nam, the most obvious deposit is a red, somewhat argillaceous sand, 

 correlated in its general composition and compactness with the Benin 

 Sands. The sand forms hills rising to a height of at least 250 feet 

 above low-water Niger. At the bottom of the valleys and in the 

 1 ' Government Gazette, Protectorate of Southern Nigeria ' vol. vi (1905) p. 287. 



