The Scottish Naturalist. 243 



of the great ice-sheet. At first, and for a long time, permanent 

 snow would be confined to the higher elevations of the land, and 

 glaciers would be limited to mountain-valleys : but as the tem- 

 perature fell the snow-line would gradually descend, until at last, 

 probably after a prolonged period, it reached what is now the 

 sea-level. Thus the formation of neve and glacier-ice would 

 eventually take place over what are now our low grounds, and 

 other tracts also, which are now submerged. It is quite impos- 

 sible that the vast sheets of ice which can be demonstrated to 

 have covered Scotland, a large part of England, Ireland, Scandi- 

 navia, and North Germany, and even the limited area of the 

 Fasroe Islands, could possibly have been fed by the snow-fields 

 of mountain heights only. The precipitation and accumulation 

 of snow, and the formation of neve and glacier-ice, must have 

 taken place over enormous regions in what are now the tem- 

 perate latitudes of Europe. 



It is obvious that the direction of ice-flow in the basin of the 

 Irish Sea opposite the south of Scotland and the west of Eng- 

 land, while preserving a general southerly trend, would vary at 

 different periods. Before the mer de glace in that basin had 

 attained its climax, there must have been a time when the ice, 

 streaming outwards from the high grounds of Cumberland, was 

 enabled to push its way far westward out into the basin of the 

 Irish Sea. At that time it was still able to hold its own against 

 the pressure exerted by the Scottish ice. But as the general 

 mer de glace increased in thickness, the course of the Cumberland 

 ice would be diverted ever further and further to the south-east, 

 until, eventually, the Scottish ice came to hug the coast of Cum- 

 berland, and to overflow Lancashire in its progress towards the 

 south-east. So gorged with ice did the basin of the Irish Sea 

 become, that a portion of the Scottish ice was forced over the 

 plain of Cumberland and up the valley of the Eden, where it 

 coalesced with the ice coming north from the Shap district, and 

 thereafter flowed in an easterly direction to join the great mer de 

 glace of the North Sea basin. 



Thus the " intercrossings " of the Criffel and Cumberland 

 erratics described by Mr Mackintosh receive a ready explana- 

 tion by the land-ice theory. Nor do the " intercrossings " of the 

 Welsh erratics with those derived from Scotland and Cumberland 

 offer any difficulty. The ice coming from the Welsh mountains 

 would naturally be deflected towards south-east by the ?ner de 

 glace that streamed in that direction, and might quite well have 



