130 I. C. RUSSELL URFACE GEOLOGY OF ALASKA. 



Alaska have been accumulated. It seems to me that this must also be the 

 explanation of the origin of all frozen deposits which* contain alternating 

 strata of clear ice and of frozen layers of mud and peat like those exposed 

 in the borders of the tundra and along the banks of the Yukon. 



Depth of Frost in On Arctic. — As recorded by K. E. Von Baer,* the ground 

 at Yakutsk, Siberia, is froz< n to the depth of 382 feet. It has been assumed 

 by various authors that the great depth of ice in this and other similar 

 instances is due directly to surface temperature, the downward limit to which 

 the winter's cold can penetrate being limited by the internal heat of the 

 earth. Before accepting this explanation as final it should be ascertained 

 whether the strata at the localities where a great depth of frozen material 

 has been encountered might not have been frozen progressively as they were 

 laid down. 



Being skeptical as to the influence of the low temperature of northern 

 land.- mi the strata at a depth of two or three hundred feet below the surface, 



1 consulted R. S. W Iward, of the V. S. Geological Survey, who has kindly 



furnished the following discussion of the question: 



The considerable depth below the earth's surface to which frost or the*temperature of 

 freezing i* known to penetrate in the Arctic regions, raises the interesting question of 

 the relation between the thermal properties of the earth's crust and the time and depth 

 of penetration. When any portion of the earth's Burface is subjected to a temperature 

 differing from that of the crust below, the process of heat diffusion or How of heat from 

 the warmer t<> the colder parts of the crust is at once Bet up. The rate at which this 

 process goes "ii and the resulting distribution of temperatures will depend, for any 

 given Bet of temperature conditions, on the conductivity and thermal capacity <>t' the 

 crust. Within such ranges of temperature as we have to consider here the conduc- 

 tivity and thermal capacity of the crust will remain invariable, and they will enter 

 the relation Bought as a ratio, which ratio is called diffusivity. With a constant dif- 

 fusivity, therefore, the form of the relation in question will be determined by the 

 temperature condition-. Of these a variety can be imagined ; but a sufficiently defi- 

 nite idea of the nature <>f the process may be gained by supposing that at the begin- 

 ning of the time the crust to a depth of a thousand or two thousand feet has a uniform 

 perature, and that the Burface of the crust from and alter the initial epoch is main- 

 tain i. -taut temperature. The maintenance of a constant temperature is 

 tically what results at the surface when a considerable portion of it i- covered by 



iand ice i in .lour. Roy. Geograph. Soc. London, vol.8, 1838, pp. 



i and subsoils of northern lands is also treated by the 

 ■ 



depth of frozen strata a( fakutak]; in Jour. Roy. Geograph. Soc 



:»• of the earth in Biberia; in Jour, Franklin In-i. N. B., vol. 



rhich ii Is desirable to make on the frozen soil of 

 ondon, vol. 9 1939, pp, 1 it I 

 John 1 America; In Edinburgh New Phil, lour, vol. 



II, it 1 1' 



■ 

 1 1. ii imer Thomas Corwin in the Arctic 



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