appendix: review and critique 479 



Taylor (1913.1) in the methods of making the estimates. Leverett is of 

 the opinion that the Niagara estimates can not be more than 5,000., or at 

 most 10,000, years out of the way; that the life of Niagara must have 

 been at least 20,000 years, and that it may have been 35,000 to 40,000 

 years. The Niagara Falls Folio enables lis to judge as to the quality of 

 Taylor's work and the value of his estimates. Spencer's methods are 

 brought out in his work on Niagara published by the Canadian Geological 

 Survey. 



(12) Leverett considers that, inasmuch as the ice of North America 

 is likely to have been reduced to a small field in the part of Canada that 

 is difficult of exploration, it may be some time, in the present sparsely 

 settled conditions, before we can correlate the position of the ice with 

 the Daun substage, or even with substages corresponding to the Gsclmitz 

 and the Buhl of Penck"s classification. These may all be found in the 

 wilds of Canada. 



VIEWS OF WILLIAM G. ALDEN, OF THE U. 8. GEOLOGICAL SURVEY 



(13) William C. Alden agrees with Leverett (February 17, 1922) 

 that it is not possible to substitute eustatic (sea movement) for diastrophic 

 (land movement) as Deperet has done. While it is probably true that 

 the net result of all crustal movements was downward, under gravity 

 action, yet there have undoubtedly been upward earth movements both 

 widespread and local; to these diastrophic movements Alden believes 

 all changes of sealevel are attributable, except those actually due to the 

 abstraction of water for storage in ice-sheets, and the subsequent return 

 of the water to the sea-basins. 



(14) As regards the beach levels, Alden remarks that it is very inter- 

 esting to have the data brought together in the way Deperet has done, 

 but that the results can not be regarded as final ; nor is it probable that 

 we can establish the Pleistocene classification on the basis of sea-beach 

 levels. Only where direct connection is traceable between the glacio- 

 fluvial terraces and the marine terraces might there be a basis for at 

 least tentative correlation between the glacial and marine phenomena. 

 There is an opportunity to test out the matter of correlating glacial and 

 marine features right in the vicinity of New York, and it may be hoped 

 that the coordination made by Deperet will be a stimulus to American 

 glaeiologists to work out the relations carefully. 



VIEWS OF EMMANUEL DE MARTONNE AND DOUGLAS W. JOHNSON 



(15) Emmanuel de Martonne writes March 29, 1922, in reply to a 

 number of questions raised by Douglas W. Johnson, that he was at first 



