part 2] MODE OF TRANSPORTATION BY ICE. 71 



the sheets decrease from the top and increase from the lower 

 surface, for which the data are not yet sufficient to provide a 

 conclusive proof. Such data would be very easy to obtain by 

 methodical measurements of one or two quantities, and, moreover, 

 such measurements would probably settle the limits of thickness, 

 depth of water, etc. at which freezing from below can take place. 



The numerous instances of raised muds already found prove that 

 the vertical transport of material by ice is going on over a wide 

 area and with considerable activity. There is no doubt that only 

 the difficulty of seeing the deposits on snow-covered moraine has 

 prevented the discovery of many more occurrences than have been 

 so far reported. 



In short, there is here a process of transport and deposition going 

 on, which in the aggregate must assume large proportions. Owing 

 to the configuration of McMurdo Sound most of the effects of the 

 process are not perpetuated, since the raised muds float away on 

 the ice as it breaks off. If the northern portion of the Sound 

 were partly closed by large islands, we should doubtless find them 

 covered with silt and muds containing: shells and mirabilite. 



Conclusions. 



The importance of this discovery and the theory that is here 

 offered to account for it does not lie so much in the explanation of 

 these particular deposits in a remote region of the world, as in the 

 analogies which it may afford for the origin of similar deposits 

 elsewhere. 



We have seen that the conditions necessary for the process 

 appear to be reducible to two : (1) a high rate of surface-thaw to 

 more than counteract the precipitation and produce clear ice. and 

 (2) a comparatively stagnant body of water under the ice-sheet. 

 These conditions are liable to be found in any sheltered bay or gulf 

 that has high sides to aid in the thaw, conditions which must be 

 present in the North just as in the Soaath. 



The aaaaze of sounds and deep gulfs north of North America 

 would therefore be ideal ground for such a process, and \ have 

 little doubt that it is going on there. On reading the descriptions 

 of ' raised beaches' from that region, one is much impressed by the 

 constant reference to the wonderful preservation of the material 

 and the peculiar associations of organisms, features that are typical 

 of the raised laauds of McMurdo Sound. Laminaria, for instance, 

 have been found at a height of 200 feet with their characteristic 

 smell still recognizable, bivalves with the cartilaginous hinge still 

 perfect, and so on. These deposits appear to have been universally 

 ascribed to recent elevations of the land, and the issue is certainly 

 clouded by unassailable evidence to that effect ; but I think that 

 closer investigation will show that the other process lias been at 

 work also. 



In Spitsbergen, again, the requisite conditions prevail at the 



