E. B. Hoicorfh— Traces of a Great Pust-GIacial Flood. 515 



destro3^ed first, and onlj^ the harder bones and rock debris holding 

 out to the last. The whole mass would become more intermingled. 

 In the case of the Sangatte Drift the materials do not appear to 

 have travelled far, the lower portion of it seems to consist of pure 

 chalk-rubble derived from the adjacent lower chalk, and the upper 

 parts being full of flints which probably came fi'om a more distant 

 point of the same range of hills. The whole mass seems to have 

 been checked and thrown down after but very little wear, and in a 

 manner comparatively independent of the specific gravity of its 

 component parts : whereas if the action which accumulated these 

 materials had been slow, gradual, and long-continued, they would 

 most likely have been sorted according to their specific gravities ; 

 and more particularly as all the fragments in any given layer would 

 have been subjected to a force acting comparatively with equal 

 power, and in an equal manner they would necessarily exhibit a 

 nearly like amount of wear ; varying in the different specimens 

 abcording to their hardness, but the measure would be alike for all. 

 In this, and the analogous case at Brighton, an impalpable chalk-silt 

 would, I apprehend, be incompatible with coarse siliceous sands — ■ 

 worn pebbles with coarse angular flints — and entire and perfect 

 bones with others, some of which are broken and others rolled and 

 worn." 



These are the views of the Nestor of Post-glacial G-eology, Mr. 

 Prestwich, as announced in 1851, and they are the views he main- 

 tains still. Before quoting a later opinion of his I would intercalate 

 a passage from a published paper read in 1860 by the Rev. 0. Fisher. 

 In describing the denudation of certain parts of South Britain he has 

 some remai'ks very germane to our subject. He referred to the 

 existence of evidence of torrential action of water in several Chalk 

 districts, for instance, ''the perfect drainage system of the dry valleys 

 of Salisbury Plain and other extensive tracts of chalk downs, the 

 loose flints filling the bottoms of such valleys, and the immense 

 blocks of tertiary pudding-stone and 'Druid Sandstone' scattered 

 along the bottoms of chalk valleys, as in the Portisham and Bride- 

 head valleys near Weymouth, and the Marlbrough ' Wethers ' in 

 Wiltshire. Mr. Fisher also thinks that he sees evidence of the 

 friction of a great body of water rushing down a hill-side in tHe 

 manner in which vertical or nearly vertical strata are usually bent 

 over at their exposed edges." 



To revert to Mr. Prestwich. In a paper on the " Phenomena of 

 the Quaternary Period in the Isle of Portland and about Wej'mouth," 

 read before the Geological Society, on June the 10th, 1874, after an 

 elaborate examination of these surface deposits he says, " 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 laud 

 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 



