272 SUPERFICIAL DEPOSITS 



It is doubtful, therefore, whether the cracking open of the domes near White Island 

 can be due to the presence of mirabilite. That phenomenon at present is unsolved. 

 Provisionally the explanation above suggested of settlement of old sea ice around 

 large boulders may perhaps account for the curious cracked domes of ice at Back- 

 stairs Passage. It may be suggested as a possible explanation that mirabilite 

 may have been distributed in a small proportion throughout a large mass of 

 old sea ice, or possibly old lake ice, and subsequently, acting under the law of 

 affinity of like for like, in the case where one mineral is present in smaller pro- 

 portion in another mineral, have gradually withdrawn itself from the other 

 mineral (in this case ice), and concentrated itself upon certain centres where con- 



M'Crummer 

 ; Granite 



Larsen Glacier 



Partof M'Gerlache 



Glaciated domes of Granite. 



Pressure ridges partly in old glacier ice, 

 partly in old sea ice, due to advance of 

 the Drygelski and Larsen Glaciers to 

 the left of M^Crummer. 



Line of Moraine cones 

 and marine muds 20f. 

 above sea, resting on 

 cones of old glacier ice. 



Fig. 64. Rough Sketch of Upthrust Marine Moraine Cones, Backstairs Passage Bay 



cretionary groups of mirabilite ciystals may have formed, subsequently added to 

 by accretion, and thus these masses may have exerted an expansive force upon the 

 ice around them. 



From what has been said, it will appear that this locality presents many 

 fascinating problems which yet await solution. One conclusion which possibly may 

 be deduced at present is that in recent time the ocean has here undergone a negative 

 movement of at least 20 feet, possibly as much as 600 feet. The evidence of the 

 ostracoda, according to Mr. Chapman, agi'ees with that of the foraminifera, " for 

 they seem to indicate deposits formed at a far greater depth." Descriptions of the 

 organisms by Mr. F. Chapman, Mr. C. Hedley, and Mi". E. F. Hallman are given 

 in the second volume of this Memoir. 



