40 



JOSEPH BARRELL 



large a volume. For instance, the easterly drift of the water facing 

 the Nile delta may have carried considerable mud in suspension 

 to beyond the line assumed here as its limits. In consequence, the 

 hypothetical 2,000-meter contour should be drawn perhaps much 

 closer to the coast of Palestine than has been done. Beneath the 

 Niger delta the contours lie close together on the west but have 

 been drawn as spreading apart toward the east. It would perhaps 

 be nearer the truth to project the steep character of the coastal 

 slopes to the east of the Niger delta under it to where the contours 

 meet the chain of volcanic island mountains extending from the 

 Cameroons out to sea. This appears to be especially probable, 

 since Buchanan has shown that the gentle slopes of the Guinea 

 coast even beyond the limits of the deltas, and extending from 



2sokm. 200 



n Sealevel 



Fig. 2. — -Vertical section of the delta of the Nile on A-A, Fig. i. Horizontal 

 scale i: 5,000,000. Vertical scale 1:200,000. Area of section, 295 kilometers. 



long. 2°3o' E. to lat. 8° S., are mantled throughout by very soft, 

 black, oozy mud, characteristic of river estuaries. 



All the way down the coast as far as Loanda, lat. 8° S., the same gentle 

 gradients and the same very soft river mud were found. It appears that the 

 land debris brought down by the Niger and Congo, and by other less impor- 

 tant rivers, is collected and concentrated in this district. The prevailing 

 current past the mouth of the Congo is a northerly one, while all along the 

 coast from Cape Palmas to the Niger an easterly current sets. These help 

 to confine the drainage matter of both rivers to a comparatively small extent 

 of Uttoral. If from the soundings west of Cape St. Paul we compute the 

 mean continental slope, we find that the 500-fathom line is at a mean distance 

 of 4.1 miles, the 1,000-fathom line at 11. 7 miles, and the 1,500-faLhom line 

 at a distance of 17 miles from the loo-fathom line. If it is assumed that in 

 the absence of the Niger and the Congo the continental slope would be much 

 the same as the average found in the profiles west of Cape St. Paul, it may be 

 concluded that the excess of mud forming the flatter talus along the coasts 

 affected by these rivers is due to the mud brought down by them.^ 



' J. Y. Buchanan, "On the Land Slopes Separating Continents and Ocean Basins, 

 Especially Those on the West Coast of Africa," Scottish Geographical Magazine, May, 

 1887, pp. 7, 8. 



