246 TRANSACTIONS AND PROCEEDINGS OF TIIK [Sess. lxvi. 



directly into snow, instead of condensing it into rain, 

 were also essential. If we assume that a belt of land of 

 considerable altitude existed along a zone joining Scandi- 

 navia and Britain, and that the so-called " Gulf Stream " 

 and its aerial accompaniment, the vapour-laden winds, were 

 in full operation close to the western margin of the land 

 throughout the whole period, it seems to me that nothing 

 else is required to account for the facts in question. 

 Elevated tracts of land, lying in the path of currents of air 

 heavily charged with moisture, are the chief requisites ; 

 and so long as the elevation was maintained above a 

 certain level snow would be precipitated instead of rain, 

 and glaciers and ice-sheets must, from the very nature of 

 the case, have accumulated upon the land. 



Now it is thought, by many geologists, that the earth's 

 crust is everywhere more or less in the condition of unstable 

 equilibrium. If natural forces remove much rock, for 

 instance, from a limited area, and then transfer it to an area 

 adjoining, a certain amount of adjustment of the earth's 

 crust must ensue. The land slowly rises, to a small vertical 

 extent at a time, where the load has been eased off ; and it 

 slowly sinks, also to a small vertical extent, at the other parts 

 where a load has been put upon it. Now, rain falling upon 

 the land does not remain there, but either flows off- or is 

 evaporated, or, more usually, it does both. If snow falls 

 and does not melt, but passes into ice, the load remains, 

 and must accumulate, if thawing does not ensue, or if the 

 ice does not find its way off from the land in the shape of 

 bergs. There is reason to believe that the ice, after a long 

 period near the climax of the Age of Snow, was several 

 thousand feet in thickness in the neighbourhood of the 

 hioher mountain masses. Each thousand feet of thickness 

 presses upon the surface beneath it with a weight equivalent 

 to something more than twenty-five tons to the square foot. 

 Hence the aggregate thickness of the glacial envelope, even 

 in the case of North Britain, must have been enormous 

 beyond conception. It has seemed to me for many 

 years back that the effect of so vast an accumulation was 

 to depress the part of Britain where the load was greatest,^ 

 and perhaps to affect the parts adjoining to a certain extent 

 ^ As Mr. T. F. .Jamieson, of Ellon, was the first to suggest. 



