76 Rev. J. F. Blake — Form of 8edimentari/ Dejjosiis. 



since 1828 in its range between Cape Finisterre and the Lizard. 

 Absence of anything that can represent the theoretical rapid slope 

 cannot, therefore, be brought against the theory, but it is another 

 thing to show that this actual slope has anything to do with the 

 theoretical. This is what Godwin-Austen writes on this subject:^ 

 " Of the true nature of such a sudden line of depression we can at 

 present only form conjectures. It may represent lines of old 

 escarpments ; or, should lines of sea-cliff have gone down rapidly 

 into sea-water where no mechanical action could modify them, 

 such features would be preserved ; lines of faults and upheaval 

 would also present such unequal soundings ; but the outline is 

 too irregular to represent the termination of the sedimentary mass 

 of the present seas, besides which we have constant indications of 

 a, surface of bare rock." On this it may be remarked that the 

 interpretation recently put upon this slope by Professor Hull, 

 following the lead of Professor J. W. Spencer in America, had 

 already been suggested as a possible one by the writer here quoted. 

 We note also that the possibility of its representing the termination 

 of deposits was admitted ; but this interpretation was rejected for 

 local reasons. 



These reasons require an answer at once. The particular district 

 to which the remarks of Godwin-Austen refer is one in which the 

 result of sedimentation is masked by the irregularity of the previous 

 sea-bottom. It is where the submerged continuations of Brittany 

 and Cornwall project above the general submarine surface. Both 

 countries are terminated with bosses of granite, and this feature 

 is continued first in the islands of Ushant and Scilly, and then 

 by a pair of banks on which granite fragments are found, hence 

 the irregularity and the bare rocks in the region within the 

 1 00 fathom line. 



But if we make comparisons in less exceptional localities we 

 find remarkable confirmations of the idea that the slope is due to 

 the termination of deposits. There is here copied (by his kind 

 permission) a portion of the map - prepared by Mr. Hudleston for 

 his paper " On the Eastern Margin of the North Atlantic Basin," 

 which has the advantage of not being drawn for the purpose of 

 proving the present theory (Fig. 3). Compare the lines marked 

 n-a and b-b. The first is drawn directly outwards from the 

 south-west of Ireland, south of the Shannon. Here there are no 

 great detritus-bearing rivers, and the contour-lines are spaced with 

 remarkable uniformity. The second is drawn opposite the opening 

 of St. George's Channel, which may be considered as a large tidal 

 estuary bearing much detritus seaward. Here the 100, 500, and 1,000 

 fathom contour-lines are much bulged outwards, while the spaces 

 between the 1000-1500 and 1500-2000 lines are reduced to 

 a minimum. Thus, where there is no deposit the continental edge 

 is scarcely marked at all, and where we may suppose that 

 there is much deposit taking place the slope is very sharp indeed. 



' Q.J.G.S., vol. vi, p. 86. 



2 Geol. Mag., 1899, Dec. IV, Vol. VI, PI. III. 



