DENUDATION BY WATER, 
89 
sprinkling of the finer disintegration-products of the granite which abundantly litter 
the surrounding area. 
These cavities in crystalline rocks apparently resemble the cavities in granite 
observed by Mr. F. F. Tuckett * and Professor T. G. Bonney f in Corsica and by the 
Rev. R. Baron J in Madagascar, but the incrustation of calcium carbonate shows that v 
wind is not the only factor involved in then - formation. As in Corsica, many 
saucer-like depressions and a few potholes were observed, and seem to mark stages 
in the development of the completed cavities. Internal incrustations do not seem 
to be recorded, but Mr. Baron mentions a “ white powder alkaline to the taste ” 
as occurring in the hollowed blocks of Madagascar. 
Water-action. — Water, as an agent of denudation in South Victoria Land, is 
at present a factor of limited import- 
ance (Figs. 51, 52, 53). On glaciers 
it merely washes away the finer 
material already thawed out of the 
ice. On bare rock it seldom appears, 
but along the south side of the Kukri 
Hills and in other places a marked 
water-channel occupies the marginal 
ice-area, and in summer water flows 
along the junction of ice with rock. 
Water, therefore, may undercut rock- 
cliffs and tend to widen and terrace 
the sides of valleys. Any ice thawed 
away by water is at once replaced by 
the advance of fresh ice, a process 
which tends to render permanent the 
course of the water-channel. Actual 
undercutting of rock-cliff was only 
seen occasionally, but at the foot 
of the hill D, along the Cathedral Rocks and along the foot of the granite hills 
G 3 , was most evident. 
During the summer, water everywhere distributes mud and sand over 
the ice. Much of this mud is derived from the moraines which protect 
ridges of ice, and the running thaw-water sorts sand from gravel and fine mud 
from sand. In this way stratified and false-bedded sands and gravels may be 
derived and appear among morainic accumulations (Fig. 52). Channels cut in the 
floating glacier-ice are common at the head of McMurdo Sound, and during summer 
Fig. 52. — Water separating Mud prom Gravel in the 
Moraines on Minna Bluff. 
vol. i. 
* Tuckett, Geol. Mag., Dec. Y, 1904, vol. i, p. 12. 
f Bonney, Geol. Mag., Dec. V, 1904, vol. i, p. 389. 
t Baron, Geol. Mag., Dec. V, 1905, vol. ii, p. 17. 
N 
