78 Rev, J. F. Blake — Form of Sedimentary Deposits. 



the map (Fig. 3) already quoted, the river Minho is an example. 

 This descends almost straight from the mountains of Asturias, and 

 has a short course. It is therefore rapid and muddy, and the line 

 e-e drawn from its mouth outwards shows the deflection towards 

 the shore of the upper contour-line and from the shore of the lower 

 •contour-line, in almost too exact conformity with the theory. The 

 Douro, though a longer river, has not so rapid a descent, and the 

 inflection of the contour-lines opposite its mouth do not go beyond 

 that of 100 fathoms, and thus do not appear on the map, but the 

 charts show a marked inflection of the 50, 80, and 90 fathoms 

 contour-line. Such smaller inflections must be similarly looked for 

 in closely surveyed charts, and will be found, for instance, all round 

 the coast of India. 



There is less reason to quote examples of the actual occurrence 

 of this expected inflection, as it has already been dwelt upon by 

 those who regard it as the indication of a submerged river channel. 

 We have seen, however, that for the production of a depression 

 opposite the river's mouth there is no necessity for the river to have 

 once flowed in it, provided that the river-current now flows over it 

 and protects it from deposit. From the instances thus quoted we 

 must except the Congo, the gorge opposite the mouth of which 

 appears to be due to the same cause which guided the river to its 

 actual course. This is shown by the gorge extending up the river 

 itself, " a depth of 150 fathoms being found 20 miles within its 

 mouth." ^ This " is not due to erosion by the river, for the current, 

 strong though it is, does not extend more than 20 fathoms from the 

 surface." The author here quoted, who like Godwin-Austen has 

 himself accompanied the sounding-line, is so much in accord with 

 the theory propounded in this paper that a further quotation is 

 much to the point. " The existence and persistence of the canon are 

 due to an agency which prevents the mud brought down by the 



river being deposited along its axis The bottom of 



the canon, or gully, would thus resemble more nearly the original 

 form of the bottom of the sea before the Congo discharged its waves 

 into it than the flatter and shallower bottom on each side of it. 

 In fact, the canon has been built up, not hollowed out. In how far 

 a crack in the crust of the earth may have had to do with the depth 

 and position of this caiion it is impossible to speak certainly, but 

 the preservation and accentuation of it are certainly due to the 

 prevention of the deposit of sediment." This recognizes the agency 

 here invoked, but does not apply it to the production of the gorge. 

 It could not, in fact, have produced the whole of it, as the bottom 

 of the shallower sea at the sides is marked in many places within 

 forty miles of the land as ' stony.' 



The bulging seawards of the lower contour-lines can only be 

 looked for in large rivers or currents, or in specially rapid ones on 

 quickly sloping shores: otherwise they are liable to be modified by 

 oceanic currents. But a very remarkable bulge is seen in the case 



' J. G. Buchanan: Scottish Geogr. Mag., yoI. iii, p. 222. 



