INTERGLACIAL EPOCHS. 267 



10 to 20, and in some places exceptionally to 60 feet above the 

 sea, which mark the limits reached by the submergence of the 

 epoch in question. The shells indicate a climate very much 

 like that of the present, but they have upon the whole a some- 

 what more northern facies. How long our area continued 

 depressed to the extent now indicated can only be conjectured, 

 but time was required for the erosion of beaches, and for the 

 accumulation of the massive beds of sand and gravel that 

 extend over considerable areas in the north-west of England, 

 and in Ireland. 



By and by, however, as the climate continued to deteriorate, 

 the land began to re-emerge, and eventually attained a higher 

 level than the present, but how much higher it is impossible to 

 say. Snow now gathered thickly upon the mountains, and 

 glaciers crawled down the valleys and deployed upon the low 

 grounds ; the last glacial epoch had fairly set in. In Scotland 

 the ice-streams became confluent, and the snow, precipitated 

 heavily over all the Lowlands, gradually accumulated to form an 

 ice-sheet hardly less massive than any of those which had gone 

 before. We know from the direction of the rock-striations and 

 the carry of the stones in the youngest boulder-clay of Scotland, 

 that the Scottish and Scandinavian mers de glace of this epoch 

 were coalescent. The ice, ploughing over the surface of the 

 country, swept out the more or less loose deposits of freshwater 

 and marine origin, which had formed during the preceding 

 interglacial epoch, and left only a few patches here and there 

 as monuments of what had once been. The ice-stream that 

 crawled down the Moray Firth was forced to overflow Caithness, 

 and in doing so it rolled forward with its bottom -moraine a 

 confused assemblage of shells belonging to different zones, which, 

 during the preceding interglacial epoch, had gathered upon the 

 submerged low grounds and what is now the bed of the Moray 

 Firth. Hence the bottom-moraine of the mer de glace, which 

 overwhelmed Caithness, contains many broken, crushed, and 

 striated shells, scattered through its mass in the same manner 

 as the stones and boulders. We meet with the same phenomena 



