222 



J. W. SPENCER — SUBMARINE VALLEYS 



from 3 miles (that of the Hudson) to 5 or 10 miles, or where farther 

 down the continental slopes the valleys open into embayments of 20 or 

 30 miles, even that breadth is no greater than can be seen in the lower 

 reaches of many land valleys. It is seldom that we are able to restrict 

 the channels to their actual breadth for want of closer soundings, such 

 as have been made along a part of the Hudson valley and along the sub- 

 merged extension of the Congo river, the last of which I may be per- 

 mitted to refer to as a most detailed piece of work in revealing buried 

 channels. Here the soundings were taken so as to obtain contours at 

 given depths apart, which were often not more than half a mile. Thus 

 Mr J. Y. Buchanan* found the depth of the river to be 900 feet at a dis- 



Isobathic Contours from. souruUrws oil' 

 theAdmiraJLty Chart N°604. 



Figure 1. — Submarine Channel of the Congo River. 

 Soundings in fathoms. 



tance of 20 miles above its mouth, where there is an obstructing bar. 

 At 35 miles from the coast line the canyon has a breadth of 6 miles and 

 a depth of 3,000 feet below the submerged plateau. The 6,000-foot con- 

 tour of the continental slope recedes landward for 30 miles at this point. 

 Beyond, Professor Edward Hull finds that the valle}^ at over 7,500 feet 

 indents the great slope for 20 miles landward. On account of the ex- 

 cellency of this study, the map of the Congo channel is here reproduced. 

 Again, outside the region of the present study we find many illustra- 

 tions better revealing the form of the valleys than those so far deter- 



* Chart taken from "The suboceanic river valleys of the west African continent," etcetera, by 

 Professor E. Hull. Trans. Victoria Institute, vol. xxxii, 1900. Also see Mr Buchanan's paper, 

 Scottish Geog. Mag., vol. iii, 1887, pp. 217-238. 



