46 J. PRESTWICH ON THE QUATERNARY PHENOMENA 



far from the larger fragments being at bottom, my experience leads 

 me to a different conclusion. At Sangatte I found the lower part of 

 the deposit to consist of a chalk rubble, often very fine, and the upper 

 part chiefly of fragments of flints of all sizes. At Brighton, seams of 

 chalk silt are intercalated in the mass from top to bottom ; whilst at 

 Chesilton the section distinctly shows a large preponderance of heavy 

 blocks of Portland flint and stone in the upper part of the cliff. 

 There was not a single large block of stone or flint within reach in 

 the lower part of the cliff; and again at the Bill the superposition 

 of the coarse angular debris on the fine loam and silt is clear. 



Nor can I agree with those who consider this deposit an old 

 talus, or with Mr. Godwin-Austen, who regards it as a talus formed 

 at high altitudes under great cold ; for in either case the materials 

 would, as pointed out by the latter, have arranged themselves at the 

 angle taken by loose materials falling over steep slopes; and when, 

 at first, the cliffs or slopes were steepest, the greater would be the 

 masses which would fall from them, while with diminishing slopes 

 or angles, the rubble or debris would, as a rule, become of 

 smaller size and of diminished quantity. Also if the deposit 

 were a mere subaerial accumulation, it would in all cases be 

 in close connexion with the slope or cliff supplying the materials 

 — would dip from it at a high angle, and never be carried far 

 beyond the range which that angle would subtend; whereas at 

 Sangatte and at Brighton, although the layers of the deposit are 

 turned up at a high angle against the old cliff, they are prolonged 

 in a gradually diminishing angle to a considerable distance from it. 

 At Chesilton the deposit does not even extend up to that part of the 

 cliff where the Portland Stone is in situ ; and whereas the escarp- 

 ment is 400 feet high, the angular debris, commencing at the height 

 of about 180 feet (see sketch, fig. 8 ; Sect. 5, PI. I.), is prolonged to 

 a distance from it of 1600 feet, or very far beyond that to which any 

 materials falling from the cliff, had it even been originally double the 

 height, could possibly have extended. The recent talus and old 

 debris are in fact perfectly distinct. In the case of this deposit at 

 the Bill of Portland, these features are still more decided. At 

 the base of it is a light loam foreign to the old cliff against which 

 it abuts, while the strata forming the top of the cliff are broken up 

 and thrown over this loam, and the two together extend southward 

 over the raised beach at the slight angle of 4° or 5° for a distance 

 of nearly a quarter of a mile. The old cliff itself, and the surface of 

 the old land above the cliff and of the old shore, are all levelled, and 

 form a uniform and scarcely apparent slope, their original relation 

 and levels being completely obliterated (see fig. 4, PI. I.) 



I hold that small angles such as these and such a mode of arrange- 

 ment are quite incompatible with any subaerial deposit of local origin 

 formed on the principle of a talus ; and the difficulty becomes greater 

 when we see that in this bed at the Bill there are fragments of strata 

 which not only are absent in the adjacent cliffs, but do not even at 

 present exist on the island. Not only is the fall insufficient to carry 

 the materials to the distance shown, but there is evidence of a vis 



