530 PROFESSOR J. W. GREGORY. 



Lobito, and at the height of 800 feet 5 miles inland. This difference of level 

 might be attributed to a westward dip; but at the step by which the land rises 

 from 500 to 800 feet the algal limestone occurs near the foot of the step only 

 300 feet lower than the injiata beds, and their relations can only be explained 

 by the step being a fault scarp. The faults in the Cretaceous beds, as remarked 

 on pp. 4!)'.), 501, are clearly seen at Lobito and Hanha and especially in the 

 Catumbella valley. 



A recent subsidence of the whole coastal area has been frequently asserted from 

 the famous submarine canyon off the mouth of the Congo. That submarine trench 

 has been advanced (E. Hull, 1912, p. 13) as proof of the subsidence of the whole 

 country to the depth of even 6000 feet. There seems, however, to be no evidence 

 of any such lowering of x\ngola. The existence of this canyon was first announced 

 by Stallibrass (1887, p. 391). It has also been described by Dr J. Y. Buchanan 

 (1887, pp. 222, 223). It is 1450 feet deep within the Congo estuary, off Banana Creek ; 

 35 miles off the mouth of the river it is 3428 feet deep ; and it is over G600 feet 

 deep where it notches the 750-fathom contour 80 miles from the coast. Dr J. Y. 

 Buchanan explained this canyon as having " been built up and not hollowed out." 

 He regards it as a canyon of accumulation due to the deposition of the Congo silts 

 on either side of the river mouth, like the deep channel off' the entrance of the 

 Rhone into Lake of Geneva. This view has also been adopted by the Portuguese 

 geographer Vasconcellos. The observations by Admiral Purey-Cust in 1899 

 (pp. 180, 181) show, however, that, instead of "the sea water running up the gully 

 at the bottom and returning in the upper layers, mixed with the river water" 

 (Buchanan, 1887, p. 223), and thus keeping the canyon empty by a vertical circula- 

 tion, the trench, even within the estuary, is occupied by almost or quite stagnant 

 sea water, and the bottom is covered by deep soft mud containing vegetable matter. 

 Hence the trench is being filled, though perhaps very slowly, by the Congo silts. 

 The most probable alternative to Dr Buchanan's theory is that a long stretch of land 

 off West Africa has foundered beneath the Atlantic, and owing to the recent date 

 of this subsidence the continuation of the Congo valley across the sunken belt has 

 not yet been wholly filled. Neither this explanation nor Dr Buchanan's involves 

 any great subsidence of the existing coast-land, and any such movement is disproved 

 by the physiographic evidence on the mainland. The shore of Angola, with its long 

 even lines, is quite unlike a drowned coast. 



A recent uplift of the coast near Lobito to the extent of 500 feet has been 

 suggested on the ground that modern marine shells occur at that height on the 

 plateau to the east of Lobito Bay. The aspect of the country, as seen from the sea, 

 certainly resembles a plain of marine denudation. I was, however, unable to find 

 on it any clear evidence of recent uplift. Sea-shells are often carried inland by birds 

 or by natives, and my informant promised to obtain some of these shells while \ 

 was in the interior, They were, however, not forthcoming, and it is quite possible 



