River-Valleys off the Coast of West Africa 
been of much interest, as indicating the extent of the uplift of the continent in a southerly direction. 
But here the soundings fail us; and we are left in the same uncertainty as regards the course of the 
river channel after entering the ocean in lat. 28° 38’ S. as in the case of the Niger. The day may come, 
however, when in the interests of scientific investigation, as also of oceanic telegraphy, the defects here 
referred to may be rectified. 
The Congo.—For a very full revelation of the physical features of the region extending under the 
ocean from the western coast of Africa, we are indebted to the investigations not only of the officers of 
the British Admiralty, but of those engaged in the important work of laying telegraphic cables for com- 
mercial communication—with results of the highest importance in connection with oceanic telegraphy in 
this part of the world. The following narrative of the discovery of the Congo channel is full of interest :— 
In 1887 Mr. Edward Stallibrass, F.R.G.S., when engaged in laying the cable under the ocean 
opposite the mouth of the Congo, in company, apparently, with Mr. J. Y. Buchanan, found that at 
certain positions under the surface the cable broke off by its own weight ; showing that the bed of the 
sea was intersected by some sharp obstruction or deep hollow. In order to ascertain the cause of this 
obstruction to progress, these engineers carried out a detailed series of soundings ; by means of which 
they discovered that the river channel itself was continued for a distance of 100 miles from the coast and 
down to a depth of 1000 fathoms. They produced a map with isobathic lines agreeing very closely with 
that of the author, but on a smaller scale than that of the Admiralty Chart ; and it only fails to give the 
full length of the submerged channel, which actually extends about 20 miles further out to sea than is 
shown by the chart of Mr. Stallibrass.1. The break in the cable was thus proved to be caused by the 
sudden drop alongside the edge of the submerged valley. (See Plate VI.) 
The Congo is one of the largest rivers of the African Continent, and enters the ocean in lat. 6° S. 
Its depth opposite Banana Creek reaches 49 fathoms. But at a distance of 5 miles, under the ocean, 
the soundings suddenly plunge down to depths of 228 and 242 fathoms (1368 and 1452 feet). At this 
point its breadth is 2 miles, with steep or precipitous sides. At a distance of 50 miles the breadth 
of the channel has increased to 10 miles and its depth to 813 fathoms (4878 feet), From this position 
the floor has a gradual descent for the next 57 miles till it reaches the maximum depth of 1200 fathoms 
(7200 feet) below the surface. 
The total length of the cafion from its head below Banana Creek to its embouchure is about 
122 miles. Throughout this distance, owing to the remarkably uniform slope of the floor of the ocean 
from the 100-fathom contour downwards, there do not appear to have been any great falls, or cascades ; 
such as appear on the eastern side of the continent, as in the case of the Zambesi. 
In order to realise the length of the submerged valley we may compare it mentally with distances 
with which we are familiar. For example, the submerged valley is twice the distance from Kingstown 
to Holyhead across the Irish Sea; it is more than twice the distance from London to Brighton ; it is 
longer than the distance from London to Bristol or Birmingham ; and it would require three hours to 
traverse by a train going at 40 miles an hour. We have also to recognise that the breadth of this valley 
is 7 miles near its centre, and that the cliffs are in some places nearly vertical, and rise over 2000 feet 
from the supposed bank of the stream. 
The remarkable results derived from the soundings in the case of the Congo go far towards com- 
pensating for the small number of the river-valleys we have been able to trace, owing to the paucity of 
the soundings at other places along the west side of this great continent ; but we may be well content 
with the results of our investigations, because they all tend to show, that the great uplift of the land, 
indicated by the phenomena bordering the coast of Western Europe, has been continued through almost, 
if not altogether, the whole extent of the western coast of Africa. 
1 For the first sight of this chart I was indebted to Professor Boyd Dawkins, F.R.S., and I afterwards undertook to work out the details on 
the Chart of the Admiralty. It is impossible to praise too highly the results attained by the original investigators. 
13 E 
