UPTHRUST MARINE MUDS 271 



sponges spreading over the blocks of rock belonging to the old moraines. Later 

 there has ensued an elevation of certainly at least 20 feet, and, according to 

 Mr. F. Chapman's opinion, of perhaps as much as 600 feet. If the original sub- 

 mergence and subsequent elevation has been as extensive as Mr. Chapman thinks 

 is suggested by the nature of the marine organisms, traces of this submergence 

 should surely have left theii- mark on the coast-line in the form of rock terracing. 

 There certainly is some appearance of this kind on the western slopes of Mount 

 Crummer, but the evidence is not conclusive. 



The levels of these terraces as given in the sketch are only roughly approxi- 

 mate, and, as stated, probably do not exceed about 600 feet. In regard to the 

 question as to whether, if this second alternative explanation is adopted, this 

 retreat of the ocean and complementary elevation of the land is stQl in progress 

 or not, it may be mentioned that we observed in places that the level surface of 

 the ice, apparently old sea ice in this case, was broken by small domes of ice pro- 

 jecting a foot or so above the general level and traversed by radiating cracks. (See 

 second diagram of Fig. 62.) These had all the appearance of being due to the 

 settlement of ice around some large boulder, which by its resistance caused the 

 ice to be bulged up and split open. Ferrar * records a similar phenomenon. His 

 description reads as follows : — 



" Near the isolated moraines in the bay between White Island and Black 

 Island, on floating glacier ice, there are five or six mounds 2 feet high, and up to 

 5 feet across of the same white salt.f 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 Balanus shells, 

 together with ice-scratched granite and other boulders." 



It is singular that near White Island such mounds, formed by hydrous sodium 

 sulphate (mirabilite or Glauber's salt), are associated with raised marine shells like 

 those of Balanus. Unfortunately we did not specially test the ice in the fractured 

 domes at the Backstaii-s Passage raised beach. There was nothing in their general 

 appearance to suggest that they were other than ordinary ice, but as mirabilite is 

 of course clear and translucent, it might easily escape detection when embedded in 

 ice. Ferrar does not suggest an explanation of how the White Island domes came 

 to be formed and fractured. His description is somewhat suggestive of an actual 

 expanding or swelling action of the mirabilite. This can hardly be due to weather- 

 ing, as mirabilite of course when exposed to the weather undergoes a process of 

 exanthalosis, whereby it parts with its water, instead of taking up more water 

 and deliquescing. The tendency, therefore, in the case of mu'abilite would be for 

 the mineral mass to decrease in size with weathering, and this dwindling would 

 be much accelerated by the extreme dryness of the Antarctic air in those latitudes. 



* National Antarctic Expedition. Natural History, vol. i., Geology, p. 91, Fig. 55. 

 t Mirabilite (T. W. E. D.). 



