"ROCK GLACIERS" OR CHRYSTOCRENES 



J. B. TYRRELL 

 Toronto, Canada 



■ In the number of the Journal of Geology for June, 1910, there is 

 an interesting article by Stephen R. Capps, Jr., on "Rock Glaciers 

 in Alaska" which must be of especial interest to all those who have 

 lived in Alaska or in the Yukon Territory, and more particularly 

 to those who have lived in the city of Dawson, for these latter will at 

 once recognize the similarity of the rockslides described and illus- 

 trated by Mr. Capps to "the Slide" on the face of Moosehide Moun- 

 tain at the north end of the town of Dawson, since the Slide is one 

 of the outstanding and ever-present features of the landscape to every 

 resident of that northern city. 



The city of Dawson is situated on a swampy alluvial flat on the 

 east bank of the Yukon River, just below the confluence of the Klon- 

 dike River. About a mile to the northeast of it Moosehide Moun- 

 tain rises to a height of 2,000 feet or more above the city, a spur of the 

 mountain extending down to the Yukon River, and terminating the 

 Dawson flat toward the north. 



The mountain is composed of massive basic eruptive rock or 

 diabase largely altered to serpentine, and cut by numerous jointage 

 planes which allow the rock to break readily into angular fragments. 

 Over the larger portions of the surface of the mountain the rock has 

 been weathered and decomposed to a considerable depth, and has 

 broken down into sand or rock flour, so that the natural slopes are 

 consequently gradual and gentle. But on the southwest side of the 

 mountain, directly overlooking the town of Dawson, there is a steep 

 scarped face of bare rock several hundred feet in height, at the foot 

 of which a talus of broken rock-fragments extends outward and down- 

 ward toward the river. This talus extends so far outward from the 

 foot of the scarp, and its lower portion has such a relatively gentle 

 slope, that it has somewhat the appearance of having broken away 

 suddenly from the side of the mountain; and consequently the early 



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