THE METAMORPHIC ROCKS OF ADELIE LAND 8TILLWELL. 17 



2. Frost Action. Frost has played a subordinate part in the sculpturing of this 

 area. In the summer we may get daily thawing and freezing. The thaw water finds its 

 way down rock joints, and, refreezing, tends to force open the joints and perhaps cause 

 fresh fracture. Boulders with planes of ready percolation, e.g., bedding planes, may 

 be seen completely shattered into flakes parallel to the bedding plane. Areas were 

 photographed (Plate XX., fig. 4) which consist of angular boulders twisted and jumbled 

 into a very confused state as the result of displacement by frost. These areas are most 

 marked where the drainage of thaw water is slow and impeded. In this way frost 

 action has helped to demolish the little mountain peaks and ridges. 



3. Water Action. The prevailing winds blow from the south, and, being very cold 

 and constant, do not permit much thaw. Given, however, calm weather, a clear sky, 

 and a bright sun, the thaw is rapid. Such days are not frequent. On one occasion in 

 December, 1912, the thaw water, draining off the moraines, was dammed back for a 

 while by ice. When the barrier gave way about mid-day a small cataract rushed down 

 the side of the valley in which the hut was situated, and in about three hours the stream 

 carved a channel through 6ft. of glacier ice down to bed rock. Stones and pebbles were 

 rolled along the course with great energy. 



Running water is uncommon, and is usually too insignificant in quantity to have 

 much bearing on the rock sculpturing. 



Marine erosion also must be slight on the mainland, for the weather is constantly 

 " off-shore," and an ocean swell is rarely seen, even though there is open sea throughout 

 the whole year. Except for about one month during the year the shore is protected 

 by an ice foot. 



4. Wind Action. The violence of the wind in Adelie Land is impressive by reason 

 of its possibilities. The constant blast of snow grains against the rock makes all surfaces 

 minutely rough and pitted. The effect of the abrasion on timber became very marked 

 on the roof of the hut and on all pieces of exposed box timber. The softer constituent 

 minerals in the gneiss, such as mica, are worn away much more rapidly than the harder 

 quartz and felspar. The etching is very prominent in specimens of the limestone 

 schists found on the moraines, and the harder portions are raised in strong relief. 

 Nevertheless, it is quite certain that the rocks are relatively unweathered and fairly 

 recently uncovered in comparison with the Madigan Nunatak. The wind affects the 

 topography by preventing soil deposition ; the surfaces of the rocks and moraines 

 are swept clean of all fine rock detritus that is not held down by the weight of boulders 

 or embedded in ice, and this detritus finds permanent lodging only in the cracks and 

 joint planes of the rocks. It is interesting to recall that occasionally in the winter 

 pebbles were heard to strike the roof of the hut just as if some one outside were throwing 

 stones. Grit may always be discovered when one displaces some of the larger boulders 

 on the moraines. 



SeriM A, VoL m., Part 1 B 



