



part 2] mode of transportation by ice. 59 



the marine mud were the same organisms as those found elsewhere: 

 shells, sponge-spicules, and polyzoa, generally well preserved, and 

 often in the position of growth that they would have occupied on 

 the sea -floor. 



I myself paid a short visit to the locality at a later date, and 

 was able to verify the fact that the ice on which they were resting 

 was similar in character to that of the McMurdo ice-sheet, that is 

 to say, much dissected by thaw-streams. See map (fig. 3, p. 55). 



The Mirabilite-Deposits. 



The deposits of sodium sulphate have a peculiar association with 

 those of the raised marine muds and a very similar distribution, as 

 will be seen by the map (fig. 1. p. 52). It therefore appeared to 

 me at an early date that any explanation for one should include 

 the other. A brief description of them is necessary on that account. 



The occurrences of the salt found by Mr. Ferrar, as quoted above, 

 were not visited by me ; but, from conversation with Dr. E. A. 

 Wilson and others who had seen them, I gained a very clear idea 

 of their nature. Those near White Island were found on mounds 

 of practically clear ice, generally cracked at the top like a pie- 

 crust. It must be pointed out that there is no genetic connexion 

 between the form of the mound and the presence of the salt, 

 except in so far as the association of the salt tends to lower 

 the melting-point of ice and would therefore conduce to thaw. 

 These pie-crust mounds were very common on the Koettlitz Glacier, 

 and are due to the gradual freezing of a small thaw-pool; the 

 expansion of the lower layers as they turn into ice raises the 

 surface-layer into a dome which finally cracks at the top. The 

 deeper the original pool was the higher will be the dome, until it 

 may even assume the form of a crater. 



The salt was not bedded in any way in these deposits. Speci- 

 mens from this locality were analysed by Dr. G. T. Prior, and 

 were found to be practically pure mirabilite, with 55"86 per cent, 

 of water of crystallization. 



The deposit of the same salt near Cape Barne (A), which is 

 described by Prof. David & Mr. Priestley, was visited by me at 

 the same lime as the marine muds. It occurs near one of the 

 lakes at about 80 feet above sea-level, in a mound sonic 5 yards 

 long by 2 in width. It is important to note that it is only 

 about 100 yards from one of the shell-deposits, though lower down 

 the hill. The effloresced salt on the surface is so like snow that, 

 except in the summer, it is almost impossible to tell it from the 

 numerous other mounds in the neighbourhood, and we had some 

 difficulty in finding it. 



Digging into the mound we came upon the clear hydra ted salt 

 immediately below the surface of the dry powdered variety. It 

 was perfectly pure and clear, in blocks up to a foot thick, and, 

 except for the cleavage-planes, might easily be mistaken for ice. 

 In fact, so close was the resemblance that, after digging down 



