part 2] A NEW MODE OF TRANSPORTATION BY ICE. 69 



cooled brine is well known, and occurs in Nature. It takes place 

 in the Great Salt Lake of Utah whenever the temperature of the 

 water falls below about 20° Fahr., and accumulates in such quan- 

 tities that it can be gathered from the bottom, being a source of 

 the Glauber's salt of commerce. 



The ice in the enclosed basin would continue to increase to a 

 small extent, and would enclose a certain proportion of the deposited 

 salt, especially on the borders of the basin. When the ice-mass 

 rose from the* bottom again the -enclosed salt would be protected 

 from the solvent action of the fresh sea-water which would again 

 fill the basin. Probably a proportion of other salts would be 

 -entangled in the sulphate as first deposited, some of which would 

 •drain out of it in the course of time, just as in the case of surface 

 sea-ice. The more or less impure mirabilite would gradually rise 

 through the ice precisely as the muds do, but on reaching the 

 surface would probably undergo a further purification in a way that 

 does not concern the subject of this paper. 



If we now apply this theoiy of the origin of the raised deposits, 

 we are able to recognize them at various stages of their evolution 

 from sea-bottom to high-level drift. The first stage is represented 

 by the occurrences of both salt and marine muds immediately 

 north of Black Island. The height of the Barrier immediately 

 south of this island and the existence of long crevasses between 

 it and White Island seem to point to the ice-sheet coming over 

 .a submerged ridge between the islands. The original site of the 

 muds cannot in that case be farther south than the northern side 

 of the ridge where the ice again begins to float. In fact, such a 

 position would be a very probable one for the process of freezing 

 to the bottom to take place. The muds off the north side of this 

 island may, therefore, be regarded as having only just come to the 

 surface — the first stage. 



A little consideration shows us that this point is a particularly 

 good one for making measurements, and finding out a great deal 

 more about the process. 



For, if T = the average thickness of the sheet in that area, 



V = the annual rate of movement of the sheet, 



E = the distance of the exposure from its origin, 

 and D = the annual decrease of the surface ; 

 then we have the following relationships : 



T 



= the number of years that it takes to reach the surface, 



E 

 and v = the same. 



Therefore we have four quantities, any one of which may be 

 found from the other three. Unfortunately, no measurements of 

 accuracy are available, and even the positions of the deposits 

 are only approximate, so that we cannot at present make any 



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