ETVEK VALLEYS OP THE WEST AFETCAN CONTINENT, ETC. 153 



4. The Grand Bcif^mm. — Anotlier West African submarine 

 channel is that of tlie Grand Eassani (lat. 5° N.) described 

 by j\Ir. Stallibrass. The Continental Platform is here from 40 

 to 50 miles broad, Avith a gentle slope to the margin of the 

 100-fathom contour; and across this shelf the old river 

 channel is traceable, Avith a well-defined margin to the 

 400-fathom contour and beyond. This channel is called on 

 the Admiralty Chart " The Bottomless Pit," and was sounded 

 by the officers on board the S.8. " Buccaneer " in 188(5. The 

 submerged channel is probably that of the River Akha, which 

 now^ enters the sea about 15 miles to the east of the point 

 where the channel begins. I am unable, owing to the paucity 

 of soundings, to add any further information regarding this 

 sub-oceanic channel to that given by Mr. Stallibrass in the 

 paper already quoted. 



5. The Nujer or Quarra. — -It might have been expected 

 that concurrently Avith the Aveil-developed sub-oceanic 

 channel of the Congo tliere would be one continuous Avith 

 that of the great African river, tlie Niger. This may be 

 so; but unfortunately Ave are unable to ascertain the fact, 

 because the soundings on the Admiralty Chart fail us just 

 Avhere Ave might exj^ect the channel to be found. Along the 

 Bight of Benin on both sides of the mouth of the Niger, the - 

 soundings are sufficiently numerous to enable us to trace 

 approximately the isobathic contours. shoAving that the land 

 descends from the lOO-fathom to below the l,0()0-fathom 

 contour Avith a A^ery steep, almost precipitous, gradieiit ; l)ut 

 betAveen long. 6° 30' and 7° 5' the soundings are slioAvn only 

 twice, viz., those of 228 and 270 fathoms, neither of Avhich 

 had touched bottom, and, therefore, give no certainty 

 regarding the actual depth. Until this gap in the soundings 

 is filled up the form and extent of the submerged channel of 

 the Niger, supposing such to exist, must remain unknoAvn, 



G. The Orange River. — This is the third of the great riA'ers 

 opening out on the ocean from West Africa, and it Avould 

 have been interesting to know whether or not it has a sub- 

 oceanic channel indicating vertical oscillations of the floor 

 extending to the A^ery south of the continent ; but I liaA'^e 

 only the same statement to make regarding the soundings 

 ofii* the mouth of the Orange River that I have made aboA^e 

 regarding those of the Niger. They absolutely fail us just 

 Avhere they are most Avanted for the purpose of determining 

 the existence of a submarine channel continuous Avith that of 

 the Grange River itself. 



