48 J. PRESTWICH ON THE QUATERNARY PHENOMENA 



a tergo propelling forward the debris beyond and out of reach of any 

 overhanging cliff. 



We may, I think, consider that the following points are now 

 established : — 



1. That the debris is entirely angular, and is composed, if not 

 altogether of local materials, at all events of such as come within 

 the area of drainage. 



2. That the finer material is more frequently found in largest 

 proportion at the base of the deposit, but that it recurs irregu- 

 larly all through the mass of the deposit from bottom to top. 



3. That the deposit has a rough stratification caused by the in- 

 tercalation of irregular lenticular masses of fine and coarse 

 portions, the whole having a prolonged and gradually decreasing 

 slope seaward at angles far smaller than could possibly be 

 taken by materials falling over any cliff or a sloping escarpment. 



4. That it is thickest at the base of valleys or of cliffs where they 

 debouch on the coast-line. 



5. That it contains the bones of land animals, together with land 

 and freshwater shells. 



These points afford definite grounds for speculation. The mate- 

 rials are evidently of origin which, if not altogether local, never 

 extends beyond the drainage-area of the spot ; and it is equally clear 

 from their arrangement and the distance they subtend the cliff, that 

 no mere subaerial action of weathering could have produced such a 

 deposit. Nor can I conceive the presence in any subaerial talus of 

 delicate land shells and of detached and broken bones of land animals ; 

 for the former are of species which would not frequent dry and stony 

 surfaces, while the skeletons of any of those which might happen 

 to have been destroyed by a fall, would hardly have their parts so 

 dispersed and reduced to so fragmentary state as we find here. On 

 the supposition of Mr. Godwin-Austen that the degradation of the 

 surface took place at a high altitude in regions of excessive cold, we 

 might obtain a greater propulsive power by the action of snow or 

 ice ; but still I doubt whether it would be sufficient to give rise 

 to the prolonged slopes we have noticed, while the presence of land 

 and freshwater shells, of bones of the horse, elephant, rhinoceros, 

 &c. in some places, seems irreconcilable with such conditions of 

 land. 



On the other hand it is evident that we have in this deposit a 

 surface-wash composed of the loose debris of the rocks of the 

 vicinity, of the shells and slugs of a land surface, and of the remains 

 of animals which might have frequented the same. 



It seems to me that the results may be ascribed to one of three 

 causes. Either, first, a mass of ice passing over the surface of the 

 land may have pushed forward the debris and thrown it seaward down 

 valleys and over cliffs, turning over their edges ; or, secondly, the 

 accumulations of winter snow may, on sloping surfaces, have 

 tended in a lesser degree to the same result ; or, thirdly, the transient 

 passage of a body of water may have swept the land-debris down to 



