42 Smithsonian Exploration in Alaska in 1904 



and gravel, abov^e which are fine sands with peaty and vegetable 

 material, the uppermost layer, locally known as ' muck,' usually con- 

 sisting almost exclusively of sphagnum swamp. The streams flow 

 on beds of the coarser alluvial gravel or sand, seldom touching the 

 underlying rocky floor, and are at present confined in relatively 

 shallow channels, the sides of which consist of the peaty and finer 

 alluvial material. Ponds or lakes are conspicuously absent. 



" The surface of the whole country, whether composed of ' muck,' 

 gravel, or rock in place, is almost everywhere permanently frozen, 

 and while as yet comparatively few shafts have been sunk through 

 this frozen layer, the evidence at hand would seem to show that it 

 has a thickness varying from forty or fifty feet on the higher, un- 

 covered parts of the hills, to two hundred feet in the moss-covered 

 bottoms of the valleys. Here and there, however, there are un- 

 frozen channels in the otherwise frozen layer, through which springs 

 issue from the sides of the hills, carrying water from the deeper 

 saturated, and unfrozen ground through the frozen layer to the 

 surface." 



On page 234 Tyrrell proposes the name " crystosphene " (ice 

 w^edge) for the underground masses of clear ice found in the Klon- 

 dike country, and " crystocrene " (ice fountain) for the surface 

 masses of ice formed each winter by the overflow of springs and 

 that melt away each summer. 



" 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 wdiere 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 dififer greatly. 

 Those in the bottom lands of the gold-bearing creeks of the Klon- 

 dike district vary in length from a hundred to a thousand feet, and 

 in width from fifty to one or two hundred feet, as shown by shafts 

 sunk through them at various places." 



" Speaking generally, these ice sheets are of very even and regu- 

 lar thickness throughout, though they are not strictly horizontal, 

 but approximate closely to the slope of the surface under which they 

 lie. For instance, the city of Dawson is built on an alluvial bottom 

 land declining gently from the base of a steep hill to the banks of 

 the Yukon and Klondike rivers, and a crystosphene which here 

 underlies the surface at a few feet beneath it seems to have about 



