RAPIDITY OF ROCK DISINTEGRATION. L37 



a little west of north and the glaciers ended before reaching the sea. Where 

 these glaciers deposited their morainal material has not been determined. 



The debris streams and accompanying talus slopes on the steep mountains 

 about Lynn canal, mentioned on page 135, record the amount of disintegra- 

 tion that has taken place since the retreat of the ancient glaciers. 



Amount of Disintegration. — It is difficult to even roughly estimate the 

 amount of disintegrated rock about the bases of the mountains of Alaska, in- 

 to compare it with similar accumulations elsewhere. It is my judgment 

 however, based upon personal observations, that the extent to which the 

 rocks of Alaska have been disintegrated is greater than that of the mountains 

 of Colorado or of the southern Appalachians, but less than that of the 

 Great Basin region. The vast alluvial cones of Nevada and southeastern 

 California are unrivalled by anything of a similar nature that fell under my 

 notice in Alaska. 



Glaciation. 

 previous explorations. 



The Yukon region from St. Michaels to Fort Yukon was examined by 

 W. H. Dall* in 1867. In the brief published account of the geological 

 results of this exploration it is stated that there is an absence of all evidence 

 of glaciation in the country examined. In a later publication Dall f remarks 

 on the absence of glacial records on the west coast of Alaska north of St. 

 Michaels, and states that the absence of bowlders in that region had been 

 previously noted by Franklin and Beechey. 



In 1881 John Muir accompanied the revenue steamer "Thomas Corwin " 

 during her voyage to Behring sea and the Arctic ocean, touching atUnalaska 

 and at several points on the west coast of Alaska, besides skirting the Siberian 

 coast from the Gulf of Anadyr to North cape. He also visited several of 

 the islands in Behring sea and the Arctic ocean. The geological results of 

 this voyage are presented in a paper " On the glaciation of the Arctic and 

 sub-Arctic region visited by the U. S. Steamer Corwin in the year 1881." X 



In this report it is claimed that sufficient proof is presented to show that 

 the entire Behring sea region was occupied by a vast continental glacier 

 during the glacial epoch, and that the ice flowed southward across the 

 Aleutian islands and discharged into the Pacific ocean. I have examined 

 two of the- localities visited by Muir, as elsewhere stated, and at eaeh of 

 them I looked for and failed to find any evidence to sustain his general- 

 ization. 



* Am. Jour. Sci., 2nd Ser., Vol. 45, 1868, p. 99. See also Observations od the Geology of Alaska, in 

 Coast Pilot of Alaska, First part, by George Davidson. U. 8. Coast Survey, Washington, 18< 

 195-196. 



t Bull. Philosophical Soc. of Washington, Vol. 0, 1884, p. 34. 



t In report of the cruise of the U. S. Revenue .Steamer Thomas Corwin in the Arctic Oc 

 by Capt. C. L. Hooper. Treasury Department, Washington, 1884, pp. 135-147. 



