RIVER VALLEYS OF THE WEST AFRICAN CONTINENT, ETC. 15^ 



constructed by Mv. Stallibrass, Telegraphic Engineer, especially 

 for the mouths of the Grand Bassam, tbe Niger, and the Conga 

 rivers ; and further with the special help of Professor A. Issel's 

 researches on the submerged valleys of Liguria in the Bay of 

 Genoa. These Alpine valleys having eroded Tertiary strata of the 

 late Pliocene stage, the elevation of their water-shed must have 

 been of Post-Pliocene date, and intimately associated with the 

 great Ice age ; and this is in accordance w^ith already accepted 

 theories. Tlie subsequent erosions making terraces, cliifs, and 

 canons, must represent enormous lapses of time ; and these pro- 

 tracted periods were followed, by the great submergence, probably 

 quite slowly accomplished, accompanied with the gradual formation 

 of ancient cliifs, and terraces, and the present existing coasts. 

 These last also exhibit evidences of subsequent vei-tical oscillation,, 

 sometimes on a grand scale. 



Cavaliere Jervis, F.G.S., Turin, Avrites : — 



We are led to infer from Professor Hull's investigations that 

 the duration of the Post-Pliocene period, required in order to 

 produce upheaval on the grandest scale over such a considerable 

 area, must have ushered in the Glacial period, in quite as gentle a 

 manner as that in which contemporaneous geological movements 

 take place. Both the number and relative state of preservation 

 of submarine river valleys, and the oceanic platforms would 

 likewise confirm the similar character of the subsequent 

 depression, by which the glacial zone was gradually reduced ta 

 its present limit. Further, such marked features of the submarine- 

 valleys of existing rivers, conclusively show that their still 

 emerged courses must have been already sculptured much as at 

 present. Thus, the physical features of mountains and valleys 

 at the present day (where not passing through still newer 

 strata), are but the continuation — the finishing touch, as it were — 

 of what already existed in later geological times, no intermediate 

 break having occurred. Roman structures, built eighteen 

 centuries ago, are common in towns situated in Alpine valleys,, 

 surrounded on either side by mountains many thousand feet high^ 

 in striking contrast to which the rivers now flow at a level of from 

 30 to 40 feet lower down, nor did the ancients build at the level of 

 the river. 



Thus, coming doAvn to our own times, I am of opinion that 

 more ample data are i-equired in order to establish generalizations 



