150 PROF. E. HULL, LL.D., F.K.S., F.G.S., ON THE SDB-OCEANIC 



extent of AVestern Africa, and where the descent into the 

 abyssal region down to, say, 2,000 fathoms and upwards is 

 rapid, or almost continuous, as off the coast of Ashauti 

 (Fig. 2), it is difficult or impossible to define the level of the 

 old coast during the period of maximum elevation, because 

 we are confronted with the question; — Was the bed of the 

 ocean actually raised to the extent here indicated by the 

 base of the escarpment, which is so much deeper than that 

 shown in other places, or did deep water extend to the very 

 edge of the land ? We cannot answer this question. It is 

 fortunate for our purpose that the emhouclmre of the Congo 

 valley at a depth of 1,200 fathoms is very clearly defined ; 

 but along many parts of the African coast there is apparently 

 no very marked change of gradient from beloAV tlie 100- 

 fathom contour till we reach depths of 2,000 fathoms and 

 upAvards, as is the case off Cape Coast Castle. It is possible 

 to assume that in such cases the vertical movements both of 

 elevation and depression have been greater than those 

 which characterise the submarine lands of Western Europe ; 

 and on reflection this appears probable, as it is not to be 

 supposed that throughout a coast-line of 3,000 to 4,000 miles 

 the amount of vertical oscillation would be exactly the same 

 throughout. Variations to some extent are more than 

 probable.* 



3. The Submerged Valley of the Congo. — In dealing with 

 this subject I feel that an apology is needed, because this is 

 almost the only river on the west coast of Africa of which 

 the continuation of the chaniiel under the ocean has been 

 described by previous authors. I might well have brought 

 my own investigations regarding the sub-oceanic river valleys 

 of tlie eastern side of the Atlantic to a close on reaching the 

 Straits of Gibraltai-, but wlien describing the submerged 

 channel of the Tagus, and showing to what a great depth it 

 could be traced, it became evident th;it the Straits could not 

 be regarded in any sense as a physical limit to the region ot 

 elevation and depression, but that it must have extended 

 far southwards along the coast of Africa itself From the 

 actual investigations I shall now lay before you, supported 

 as they arc to a great extent by those of other writers, I hope 



* It is to be recollected tliat the snbmerp,ed river valleys and the base 

 of the great declivity oti' the coast of the British Isles corrosjjoiuls rather 

 to the 1,000-fathoui contour, while off the coast of "Western Kurojie they 

 are represented by the 1,200-fathoni contour. 



