DENUDATION BY CHEMICAL ACTION. 
91 
December, 1903, for an area of sea-ice, six square miles in extent, was found with 
an average of eighteen inches of muddy water upon it. Some of this water may 
possibly have been produced in place, for this inundated area lay along the north edge 
of the floating glacier-ice, and during the winter-gales must receive foreign matter. 
Chemical action . — Chemical decomposition of rocks is more obvious in the dry 
climate of South Victoria Land than in other areas, for rain can usually remove 
soluble salts as fast as they form. On Hut Point all rock-fragments have thin 
incrustations of sodium sulphate (398). The incrustation is sometimes so abundant 
that the rocks look as if they have been dusted over with lime or flour ; if the loose 
surface-matter be scraped away, thin discontinuous beds of the pure salt may be seen 
dipping gently into the hill. The surfaces of many boulders in The Gap are covered 
by a lace-like network of white lines (262, 263) consisting of calcium carbonate. 
Near the north end of 
White Island a great 
quantity of perfect crystals 
of sodium sulphate (298) 
was obtained on a mound 
of the floating glacier-ice 
(Fig. 55). The percentage 
of water in this salt, as 
determined by Dr. Prior, 
was 55 '86, which is virtu- 
ally identical with that 
characteristic of pure Mira- 
bilite or Glauber Salt. 
Near the isolated 
moraines in the bay be- 
tween White Island and 
Black Island, on floating glacier-ice, there are five, or six mounds, two feet high 
and up to five feet across, of the same white salt (623). The mounds are entirely 
composed of the salt, which is in well-formed crystals, though the outer ones have 
effloresced to some small extent. The moraines near these mounds contain halanus 
shells (612) together with ice-scratched granite and other boulders (Fig. 46, p. 80). 
In one of the moraine-cones on the west side of McMurdo Sound, a bed of 
this salt (741), about eighteen inches thick, is traceable horizontally for about 
ten yards. This bed is at least 50 feet above a pond of brackish w T ater which 
occurs at the foot of the moraine. Dr. E. A. Wilson also found this salt (740) 
near the head of Discovery Gulf, and Mr. T. V. Hodgson (742) on Inaccessible 
Island. As many of the ponds among the moraines are much too saline for 
drinking, it is possible that this peculiar and abundant concentration of soluble 
salt may be due to a former crystallization from similar ponds. 
Fig. 55. — Fractured Dome in the Floating Glacier-ice, near the 
spot where Sodium Sulphate Crystals were found, two miles 
FROM THE NORTH END OF WHITE ISLAND. 
