GLACIOLOGY OF THE SOUTH ORKNEYS. 837 



plenty to be found even at sea-level in more sheltered and less exposed spots. What 

 may be called "the theoretical or climatic snow-line" [i.e. the level above which 

 accumulation is equal to or greater than the amount lost by melting, evaporation, 

 or transformation into ice on level, freely exposed areas, where there is no undue 

 accumulation through wind drift, but also where, on the other hand, the snow is not 

 swept off to a great extent) is probably some little distance above sea -level. Actually, 

 and practically, from the point of view of ice formation, in which wind-drifted 

 accumulations play a considerable part, the level of perpetual snow may here be taken 

 as coming right down to the sea-level. 



Topography of Laurie Island. 



The South Orkneys present the features of a dissected upland, whose main outlines 

 probably owe their origin to glacial action when the land stood at a higher level, 

 although the present-day rock features are largely the result of sub-aerial weathering, 

 and the rock- shattering action of frost. 



More recent depression of the land has left exposed merely the top of a carved and 

 fretted mountain ridge, whose main axis extends in an east to west direction for a 

 distance of about seventy-two geographical miles measured from Cape Dundas, the 

 easternmost point of Laurie Lsland, to the western extremity of Coronation Island. 

 Circumstances, however, only permitted of a close examination of the glaciers of Laurie 

 Island, the most easterly member of the group, and the following descriptions must 

 be taken as applying merely to this island, unless expressly stated to the contrary. 

 The period during which there was opportunity to study the glacial conditions 

 extended from 25th March 1903 to 21st February 1904, almost eleven months. 



Laurie Island is composed entirely of Silurian sedimentary rocks, principally grey- 

 wack^s. Its longest axis stretches in an approximately east to west direction, with a 

 number of narrow peninsulas branching off on both sides. These run in a N.W.-S.E. to 

 N.N.W.-S.S.E. direction (corresponding to the line of folding of the rocks), and have deep 

 bays between them. A steep serrated ridge runs as a backbone along a great part of 

 the island, with subsidiary comb-like ridges branching out into the various peninsulas 

 on either side, and these in their turn have sometimes a second series of smaller 

 diverging rock ridges. Most ridges end in a more or less precipitous cliff at the sea. 



Except towards the eastern end of the island, where the backbone dies down, there 

 is no central high level plateau on which an ice-cap can develop. There is merely the 

 narrow slope between the hills and the sea, an area which, in the case of the South 

 Orkneys, has recently been somewhat increased in extent by an uplift of the land 

 to the amount of about 15 feet. This sloping coastal zone is in many parts of a 

 sufficiently gentle gradient to allow snow to accumulate and ice to form. In other 

 parts, especially at the ends of ridges, the rock face comes down almost sheer into the 

 sea, and even along the length of the hills there are often projecting rock bosses or 

 secondary ridges which cut into the available area. 



