196 W. UPHAM — PLEISTOCENE AND PRESENT ICE-SHEETS. 



swift, brown flood, fully one hundred feet across and fifteen or twenty feet deep. 

 The stream, after its subglacial course, spreads out into many branches, and lias 

 built up an alluvial fan which has invaded and buried thousands of acres of forest. 

 In traversing the coast from the Yahtse to Yakutat bay, we crossed scores of ice- 

 water streams which drain the ice-field to the north. The greater part of these 

 could be waded, but some of them are rivers which it was impossible to ford. 



Oogenic disturbances formed the Saint Elias range since the begin- 

 ning of the Pleistocene period, for its basal portion consists of the late 

 Pliocene and Pleistocene Pinnacle and Yakutat formations, above which 

 the Saint Elias schist has been overthrust. Fossil marine shells, all of 

 which .are represented by species now living in the adjacent ocean, were 

 collected by Russell in the cliffs above Pinnacle pass at the height of 5,000 

 feet above the sea. The following summary of the history of this range 

 is given by Russell : * 



Not only was a part, at least, of the Pinnacle system deposited during the life of 

 living species of mollusks, but also the whole of the Yakutat series, the stratigraphic 

 position of which is, if my determination is correct, above the Pinnacle system. 

 After the sediments composing the rocks of these two series were deposited in the 

 sea as strata of sand, mud, etc., they were consolidated, overthrust, faulted and up- 

 heaved into one of the grandest mountain ridges on the continent. Then, after the 

 mountains had reached a considerable height, if not their full growth, the snows of 

 winter fell upon them, and glaciers were born. The glaciers increased to a maxi- 

 mum, and their surfaces reached from a thousand to two thousand feet higher than 

 now on the more southern mountain spurs, and afterward slowly wasted away to 

 their present dimensions. All of this interesting and varied history has been en- 

 acted during the life of existing species of plants and animals. 



The Muir Glacier. — According to the descriptions and maps of Pro- 

 fessors G. Frederick Wright f and H! F. ReidJ and Mr H. P. Gushing, || 

 the Muir glacier, which is situated some 200 miles southeast of Mount 

 Saint Elias, has an area of about 350 square miles, and the area inclosed 

 by its watershed is about 800 square miles. It receives many tributary 

 glaciers, whose areas are included in this estimate. The slope of the 

 main glacier for 10 miles or more next to its termination in the sea at 

 the head of Glacier bay is about 100 feet per mile. Its frontal cliffs, 

 which shed multitudes of bergs into the sea, had in 1890 an extent of If 

 miles, and rose in a vertical wall of ice 130 to 210 feet above the water, 

 which, within 300 feet from the ice-front, has a maximum depth of 720 

 feet. Between the observations of Professor Wright in 1886 and those of 



*Nat. Geog. Mag., vol. iii, pp. 172, 173. 



t Am. Jour. Sci., III, vol. xxxiii, pp. 1-18, with map, January, 1887 : The Ice Age in North America, 

 1889, chapter iii. 

 J Nat. Geog. Mag., vol. iv, pp. 19-84, with 16 plates and 5 figures in the text, March 21, 1892. 

 || Am. Geol., vol. viii, pp. 207-230, with map, October, 1891. 



