44 R. C. ANDREWS 



topography. Subsidence postdating glacial times there has cer- 

 tainly been in New Zealand and Australia, but apparently to nothing 

 approaching the depths required to sink these old ice-channel floors 

 2,000 feet or more below the sea-surface. 



Furthermore, the fact of the striking depths found in the Nor- 

 wegian, Alaskan, and Patagonian fiords, and the strong contrasts 

 presented thus with associated non-intensely glaciated areas, are 

 very suggestive. 



Rock-basin excavation along old stream channels below base- 

 level during periods of maximum ice- floods combined with slight 

 later drowning is a sufficient explanation. 



2. Cirques also appear explicable on the assumption of ice-sapping,^ 

 and find their counterparts in stream-action in rock basins excavated 

 by the undermining action of water falls. 



The magnificence of the glacial features (lakes, sound basins, 

 cliff slopes, cirques, etc.), as compared with the holes, bank-cuttings, 

 and flood-heaps formed by water, is due to the fact that in the case 

 of the one the corrading agent was confined to a trifling portion only 

 of the valley, while in the case of the other the glacier occupied the 

 whole of its valley. 



ANSWERS TO OBJECTIONS 



In H. L. Fairchild's recent glacial note^ a great number of hitherto 

 unanswered objections to glaciation as an efficient corrader are 

 advanced. To most of these the ice-flood hypothesis furnishes a 

 satisfactory answer. 



Thus (p. 19) Fairchild adduces the frequent presence of rock- 

 polishing and slight ice scratches only instead of "deep groovings 

 and cornice-like flutings" as evidence against the efficiency of ice- 

 erosion. 



Now, these smooth surfaces, slight scratches, and general absence 



1 See also Willard D. Johnson, "The Profile of Maturity in Alpine Glacial Erosion," 

 Journal of Geology, Vol. XII, No. 7 (1904) ; also Dr. G. K. Gilbert, "Systematic Asym- 

 metry of Crest Lines in the High Sierra of CaHfornia," ibid. Since writing the above, 

 Professor Albrecht Penck has sent the author a paper on " Glacial Features in the Surface 

 of the Alps," ibid., Vol. XIII, No. i (1905). In this remarkable paper the author sees 

 additional confirmation of his "ice-flood" hypothesis. 



2 "Ice Erosion Theory a Fallacy," Bulletin of the Geological Society of America, 

 Vol. XVI, pp. 13-74, Plates 12-23. 



