TRANSACTIONS OF SECTION C. G53 



cutting of its upper great gorge. Taking the ascertained rate of recession of the 

 Horseshoe fall as the principal datum, the time occupied in that work may have 

 been from 5,000 to 10,000 years, which thus becomes the measure of the time 

 which has elapsed since the emergence of the Champlain area. The measure of 

 the duration of the Champlain submergence is the time occupied in the cutting of 

 the gorge of the Whirlpool rapids. No data exist for its statement in years that 

 would be more than a guess. Such merely conjectural estimate as can be based 

 on the action, or inaction, rather, of the American fall would lead to figures nob 

 less than twenty or twenty-five thousand years. 



Remarks introductory to the Uxcursion to Niagara Falls and Gorge. 

 By G. K. Gilbert. 



10. Drift Phenomena of Puget Sound and their Interpretation. 



By Bayley Willis. 



The area from which the facts for this discussion were collected is the Tacoma 

 quadrangle of the United States topographical survey, comprising the district east 

 and south of Seattle and Tacoma. The major topographic features are the 

 channels of the Sound and the strictly homologous valleys now fiUed with 

 alluvium. These divide, and in some instances surround, plateau-like elevations 

 composed of stratified and unstratified drift that rise about 500 feet above the sea. 

 On the slopes of the adjacent foot hills of the Cascade Range drift deposits 

 occur up to and beyond 1,700 feet above the sea. Various features of the Glacial- 

 derived topography have been traced out in detail, including characteristic till 

 surfaces, morainic zones, kames, and overwash plains. The distribution of these 

 features indicates that at least the latest Glacial advance was along the valleys and 

 channels of the Sound, and that glaciers rose above and overflowed the margins 

 of the plateaus. The materials of the drift are to a large extent granite, and bear 

 evidence of prolonged water transportation. A distinct variety of till, containino- 

 numerous erratics of Tertiary volcanics, was found in localities to which it was 

 probably brouo-ht from the local centre of glaciation. Mount Rainier. The rela- 

 tion of these local Glacial deposits to the general drift indicates that the prevailing 

 drift phenomena were due to glaciers which penetrated from the north as far south 

 as the foot hills of Mount Rainier, 30 miles south-east of Tacoma. 



The detailed examination of the various features of the drift suggests the 

 hypothesis that the channels of the Sound are the hollows remaining after 

 repeated Glacial occupation of a wide valley formerly diversified by the valleys 

 and ridges of pre- Glacial topography. In the course of repeated Glacial advance 

 and retreat the earlier divides were built upon and transformed into plateau-likt' 

 eminences of Glacial drift, whereas the occupation of the valleys by Glacial ice, 

 particularly in the stagnant stages of retreat, prevented their being permanently 

 filled ; with the final retreat of the ice the molds of glaciers remained as the 

 channels of the Sound. This hypothesis is to be contrasted with that of erosion 

 due to repeated uplift and subsidence. 



11. The Southern Lobe of the Laurentian Ice Sheet. ^ 

 By Professor C. H. Hitchcock. 



The ice-sheet of eastern North America had its gathering grounds in the 

 Laurentian highlands, east of Hudson's Bay. Glaciers flowed from it in all 

 directions. Perhaps the most conspicuous discharge was to the south through 



• For a fuller account of this lobe see American Geologist, July 1897, vol. xx. 

 * The Eastern Lobe of the Ice-sheet.' ' * 



