148 POLAR PROBLEMS 



oceans all about, as contrasted with the north, or Is it because the 

 north polar regions, being uninterruptedly connected with conti- 

 nental land masses to the south, have been supplied repeatedly by 

 migrants from the south and also in circumpolar directions? 



Influence of Slope Exposure 



Considerable data have accumulated as to the influence of slope 

 exposure on the distribution of plants in our hilly districts and moun- 

 tains,^^ but we know relatively little as to the action of this influence 

 in the Arctic Regions. To reach satisfactory conclusions an all-season 

 survey should be instituted where the slope exposures are found 

 facing the different directions of the compass. The mountains of 

 northern Alaska would be suitable for such an investigation. 



Plant Succession on Surfaces Exposed 



THROUGH SoLIFLUCTION 



The slipping down of the soil of mountain slopes, or the sliding 

 action of soils on slopes less steep, is known as solifluction. It is not 

 an uncommon phenomenon in the Arctic Regions where the super- 

 ficial vegetation of mosses, lichens, and shrubs on loose, water-soaked 

 peat will begin to slide down, especially if the front of a given hill has 

 been undermined by the building of a road along its face or by dredging 

 operations in mining gold. As a result of this movement soil entirely 

 denuded of vegetation will be exposed. The succession of plants of 

 such exposed virgin soil is a matter of interest, and of deep concern 

 if the soil movement takes place near mines or established centers 

 of population. 



Plant Growth over Frozen Subsoil 



Another soil problem, which the writer has investigated in several 

 districts in his recent visit to Central Alaska, is that of the frozen 

 condition of the soil under the superficial layers, which thaw out in 

 summer. Such local observations should be extended to the investi- 

 gation of similar conditions in all parts of the Arctic realm. The writer 

 learned that on some bench lands the soil may be frozen to a depth of 

 245 feet; that on well-drained hill slopes, especially those with a 

 southern exposure, the soil is never permanently frozen but thaws 

 out in summer; that in soils which are frozen permanently to a great 

 depth the sinking of a mine shaft may reveal suddenly an unfrozen 

 area, and that this is associated usually with some ancient stream 

 bed which carries subterranean water. The gold miners have learned 



21 J. W. Harshberger: Slope Exposure and the Distribution of Plants in Eastern Pennsylvania, 

 Bull. Geogr. Soc. of Philadelphia, Vol. 17, 1919, pp. 53-61. 



A. G. Vestal: Foothills Vegetation in the Colorado Front Range, Botan. Gazelle, Vol. 64, Chicago, 

 1917. pp. 3S3-385. 



