482 MB. CHAS. DAVISON ON SNOWDRIFT DEPOSITS. [Aug. 1 894, 



Y. Nature of Snowdrift Deposits. 



1. Fineness of Texture. 



One of the most noticeable features about the snowdrift deposits 

 that I have had an opportunity of examining is their extremely fine 

 texture. When rubbed between the fingers, the material generally 

 feels smooth like flour. If it be put in water and disturbed, part sinks 

 within a few minutes, but the water remains discoloured for several 

 days. No doubt a strong wind is capable of driving, and does drive 

 much larger particles ; instances have already been given of sand 

 drifted with snow. But such particles would not be carried far ; 

 they would be easily dropped during brief lulls in the storm, and 

 perhaps dropped beyond recovery. The finer dust, however, re- 

 mains suspended in air for some time and may be carried great 

 distances. Extensive and continuous deposits from snowdrift must 

 almost inevitably be fiue-grained. 



2. General Absence of Stratification. 



When the decay of snowdrifts takes place slowly, it seems almost 

 evident that the deposits from them must be unstratified. For, as 

 each granule of snow melts, the fine dust-grains coating it subside 

 irregularly, and there is no force acting, as in currents of water, to 

 arrange them in any definite direction. Occasionally dust of larger 

 size from a nearer origin might be deposited in a snowdrift, or dust 

 of an entirely different nature, and these might form layers in the 

 future deposit. They might even give it an appearance of stratifi- 

 cation, the layers being roughly parallel to the original surface of 

 the ground. But the snow in a drift lies so irregularly and is of 

 such varying depth, the rate at which it decays depends so much on 

 the thickness of its coating of mud, and in this mud there may be 

 differential movements as it is gradually lowered by the decaying 

 of the snow below, that the probability of any final appearance of 

 stratification is rather remote. If continuous layers were, however, 

 formed, they would most likely be of a wavy and irregular 

 character. 



In connexion with this absence of stratification, I made several 

 experiments during the winter of 1891-92, one of which may now 

 be described. On a large piece of millboard, I placed (1) a layer of 

 clean snow, 25 inches long, 17 inches broad, and 6 inches thick ; 

 (2) above this a layer of snow mixed with fine dry soil, the snow 

 and soil being showered alternately until a layer 3 inches thick 

 of dirty snow was formed ; (3) on this a layer of clean snow 5 inches 

 thick; (4) a layer, 11 inches thick, similar to the second, except 

 that the dust was previously mixed with mica-flakes, most of them 

 very small; and (5) a top-covering of clean snow, 3 inches thick. 

 The appearance of the mound was carefully watched from day to 

 day. The uppermost layer of snow soon melted, and the usual 



