September 16, 1910] 



SCIENCE 



359 



as the first and second, and would rise, 

 though rarely, to above 11,000 feet; the 

 average in central Scotland would be about 

 11,400 feet, and the maximum about 13,000 

 feet. Thus, north Wales, the Lake District 

 and the southern uplands would differ lit- 

 tle in ice-productive power; while central 

 Scotland would distinctly exceed them, but 

 not more than the group around the Pin- 

 steraarhorn does that giving birth to the 

 Ehone glacier. In one respect, however, all 

 these districts would differ from the Alps 

 - — that, at 8,000 feet, the surface, instead 

 of being furrowed with valleys, small and 

 great, would be a gently shelving plateau, 

 which would favor the formation of pied- 

 mont glaciers. StiU, unless we assume the 

 present distribution of rainfall to be com- 

 pletely altered (for which I do not know 

 any reason) , the relative magnitudes of the 

 ice coming from these centers (whether 

 separate glaciers or confluent sheets) could 

 differ but little. Scotch ice would not ap- 

 preciably "shoulder inland" that from the 

 Lake District, nor would the Welsh ice be 

 imprisoned within its own valleys. 



During the last few years, however, the 

 lake-hypothesis of Carvil Lewis has been- 

 revived imder a rather different form by 

 some English advocates of land-ice. For 

 instance, the former presence of ice- 

 dammed lakes is supposed to be indicated 

 in the upper parts of the Cleveland Hills 

 by certain overflow channels. I may be 

 allowed to observe that, though this view is 

 the oiiteome of much acute observation and 

 reasoning,'^ it is wholly dependent upon 

 the ice-barriers already mentioned, and 

 that if they dissolve before the dry light of 

 sceptical criticism, the lakes will "leave not 

 a rack behind." I must also confess that 

 to my eyes the so-called "overflow chan- 

 nels" much more closely resemble the rem- 

 nants of ancient valley-sj'stems, formed by 



'" P. F. Kendall, Quart. Journ. Oeol. 8oc., 

 LVIII., 1902, 471. 



only moderately rapid rivers, which have 

 been isolated by the trespass of younger 

 and more energetic streams, and they sug- 

 gest that the main features of this pic- 

 turesque upland were developed before 

 rather than after the beginning of the 

 glacial epoch. I think that even "Lake 

 Pickering," though it has become an ac- 

 cepted fact with several geologists of high 

 repute, can be more simply explained as a 

 two-branched "valley of strike," formed 

 on the Kimeridge clay, the eastern arm of 

 which was beheaded, even in preglacial 

 times, by the sea.^" As to Lake Oxford, ^^ 

 I must confess myself still more sceptical. 

 Some changes no doubt have occurred in 

 later glacial and postglacial times; valleys 

 have been here raised by deposit, there 

 deepened sometimes by as much as 100 

 feet; the courses of lowland rivers may 

 occasionally have been altered ; but I doubt 

 whethev, since those times began, either ice- 

 sheet or lake has ever concealed the site of 

 thac university city. 



The submergence hypothesis assumes 

 that, at the beginning of the glacial epoch, 

 our islands stood rather above their present 

 level, and during it gradually subsided, on 

 the west to a greater extent than on the 

 east, till at last the movement was reversed, 

 and they returned nearly to their former 

 position. During most of this time glaciers 

 came down to the sea from the more moun- 

 tainous islands, and in winter an ice-foot 

 formed upon the shore. This, on becoming 

 detached, carried away boulders, beach 

 pebbles and finer detritus. Great quanti- 

 ties of the last also were swept by swollen 

 streams into the estuaries and spread over 

 the sea-bed b.v coast currents, settling down 



^ See for instance the courses of the Jledway 

 and the Beult over the Weald clay (C. Le Neve 

 Foster and W. Topley, Quart. Journ. Oeol. Soc, 

 XXI., 1865, p. 443). 



" F. W. Harmer, Quart. Journ. Geol. Soc, 

 LXIII., 1907, p. 470. 



