234 



/. B. TYRRELL 



their flow being but slightly, if at all, affected by the conditions of 

 the weather, or even by the most extreme seasonal changes of tem- 

 perature. In summer those that issue from the rock above the 

 alluvial deposits discharge over the surface into the nearest brooks 

 or rivers, and, except where used as local supplies of clear cold water 

 for household purposes, are rarely noticed; but in winter, when the 

 thermometer occasionally falls as low as — 60° F., the water flowing 

 out into the cold air freezes within a comparatively short distance, 

 and by the close of the winter it may have formed a mass of ice 

 many feet in thickness. These ice-masses are locally known as 

 "glaciers," and where they form along the lines of roads are often 

 serious obstructions to travel. 



But, in addition to these masses of ice formed on the surface every 

 winter, and which regularly melt away during the following sum- 

 mer, other masses are formed beneath the surface in such positions 

 that they are protected from the action of the sun and atmospheric 

 agencies; and thus it is possible for them to increase from year to 

 year to very considerable dimensions. These underground masses 

 of clear ice are also locally known in the Klondyke country as "gla- 

 ciers," but the name " crystosphene " {icpvaTaWo<i "ice"; ac^nfjv^ 

 wedge") is here suggested for them, as indicating a mass or sheet of 

 ice developed by a wedging growth between beds of other material, 

 while the name "crystocrene" {icprjVL<i^ fountain), is suggested for the 

 surface masses of ice formed each winter by the overflow of springs. 

 Crystosphenes are formed by springs which issue from the rock 

 under the alluvial deposits that cover the bottoms of the valleys. 

 As a rule, they occur as more or less horizontal sheets of clear ice, 

 .from six inches to three feet or more in thickness, lying between 

 layers of "muck" or fine alluvium, usually where the "muck" is 

 divided horizontally by a thin bed of silt or sand; and most of them, 

 as far as my observation goes, are from two to four feet below the 

 surface, though some are deeper. In area they differ greatly. One 

 observed by the writer on the shore of Daly Lake, near the southern 

 edge of the Barren Lands west of Hudson Bay, seemed as if it might 

 underlie a square. mile or more, while many of those in the bottom 

 lands of the gold-bearing creeks of the Klondyke district vary in 

 length from a hundred to a thousand feet, and in width from fifty 



