T. F. Jamieson — The Interglacial Question. 535 



directions fully 1,000 miles, and much of its thickness must be 

 reckoned in thousands of feet. The North American ice perhaps 

 attained even greater proportions. Just think of the amount of heat 

 and the time it would take to thaw such masses. There is a huge 

 difference between snow and ice in this respect. Snow, especially 

 when newly fallen, thaws rapidly, but ice does not. It melts with 

 extreme slowness, and so long as the thaw was going on and much 

 of the ice-sheet remained, the temperature of the air in Northern 

 Europe and America would not rise to any great degree. The 

 accumulation represents a storage of cold during thousands of years, 

 and the probability seems to be that the returning heat brought 

 about by the precession of the equinoxes would not always be able 

 to dispel the vast masses of ice left on the land by the preceding 

 period of glaciation. In short, the heat would all be spent in but 

 a partial melting of the glacial covering. Consequently the 

 temperature in many places would never rise so far as to cause 

 a complete reversal of climate, and thus no clear evidence of an 

 interglacial warm period would be found, but merely indications of 

 a large retreat of the ice-front. Croll, it is true, did not take this 

 view of the matter, for he conceived that the reversal of climate 

 would be complete, and that the ice would wholly disappear from 

 one hemisphere when the other was under glaciation. In this, 

 however, I think he may have been mistaken. At any rate, we 

 have no certainty that such would be the case. 



Now, in the north of Scotland we can show that the basin of the 

 Moray Firth was at one time filled with ice to such an extent that 

 the right flank of the mass flowed eastward along the coast of Moray 

 and Banff and then wheeled round the corner of Aberdeenshire, 

 where it appears to have surmounted a hill 769 feet high ; while its 

 left flank in like manner turned round over the lower part of 

 Caithness, overflowing hills there some hundreds of feet in height, 

 and producing the shelly boulder-clay of that district.^ All this 

 implies a thickness of ice in the basin of the firth to be measured by 

 thousands of feet. Now we have further evidence that this great 

 mass of ice afterwards disappeared, and that sea-water inhabited by 

 mollusca of a northern type occupied the basin up to the very top at 

 Inverness. The Northern and even Arctic character of many of the 

 species found in these shell-beds seems to show that although an 

 enormous amount of heat must have been long in action to dissipate 

 such a mass of ice, yet this heat was not sufficient to introduce 

 a decidedly warm climate, at any rate so far as the temperature of 

 the sea- water was concerned ; nor has any evidence as yet been 

 obtained in the district to indicate a warm temperature on the land. 

 This episode of an interglacial occupation of the Moray Firth basin 

 by sea-water inhabited by mollusca of a northern type was afterwards 

 followed by a return of the glacier in great force, which destroyed 

 the shell-beds and covered them with. heavy masses of boulder-clay, 

 as we see at Clava and elsewhere. 



1 Journal of the Geol. Soc, vol. Ixii, p. 13, Feb., 1906. T. F. Jamieson on the 

 Glacial period in Aberdeenshire and the Southern border of the Moray Firth. 



