552 J. B. TYRRELL 



loose rocks and ice to move downward and outward, and this tendency 

 is increased in the spring and summer when the upper portion of the 

 icy matrix becomes melted, so that the stones which were imbedded 

 in it become loosened and slide downward over each other. This 

 process of the breaking-down of the face of the almost vertical cliff 

 and the growth and extension of the talus is constantly in operation 

 year after year, so that the face of this hill of light-green serpentine 

 always has the appearance of having just been freshly broken and 

 the material at its foot of having just slidden from it, while the slop- 

 ing field of loose rock below shows abundant evidence of having been 

 recently moved to its present position. 



We have here simply a northern modification of the conditions 

 found on many hillsides where springs give rise to broken slopes. 



In the Journal of Geology, XII (1904), 232, I described some 

 springs which flow from the frozen hillsides in the Klondike and which 

 in winter issue into the cold air, and are then almost immediately 

 frozen into ice. During the course of the winter, these masses of 

 ice may assume considerable proportions, and when they form on 

 the roads or main lines of travel, they are often, on account of their 

 smooth, sloping surfaces, the occasion of much inconvenience to the 

 freighters and stage-drivers. In several instances they have also been 

 known to break up in the floors of houses, and to fill the house with 

 ice, just as they fill the spaces between the loose rocks in the heaps 

 of talus. These frozen masses of spring water are, in the Klondike, 

 locally known as "glaciers," but as this word was already fully pre- 

 occupied, I called them, on the suggestion of Professor T. C. Chamber- 

 lin, chrystocrenes. 



The spring at the foot of Moosehide Mountain in Dawson forms 

 one of these chrystocrenes, but instead of the water flowing out freely 

 into the air, it flows into a detrital mass of broken rock and assists 

 in gradually moving this rock outward from the foot of the mountain 

 toward the Yukon River, which flows at its base. 



I would suggest that the "rock glaciers" described by Mr. Capps 

 may probably have been formed in the same way as the Slide at 

 Dawson; that they are kept supplied with water flowing from springs 

 in the sides of the hills; that this water becomes frozen into a mass of 

 ice during the severe cold weather of winter; and that the ice, with 



