734 THE JOURNAL OF GEOLOGY. 



were considerable changes of. level, before the ice of the next epoch 

 reached its greatest development. 



The evidence brought forward along these lines in support of the sep- 

 aration of the epoch of the " district " glaciers of Scotland from the epoch 

 of the preceding mer de glace is such as to make it clear that the former 

 was in some measure distinct from the latter. The ice of the so-called 

 fourth epoch would seem to mark a distinct stage in glacial history, a 

 stage when the ice was more active than for a time preceding. But the 

 evidence is not such as to make it clear that the epoch of " district " 

 glaciers was so far separated from the last mer de glace of Scotland as 

 to entitle it to the rank of a separate epoch, as that term is used in 

 America. If local glaciers of the dissolving ice sheet tarried long in 

 the mountain valleys, their persistence would seem to explain some of 

 the phenomena cited as evidence of the separation of the epochs. A 

 temporary and relatively slight re- advance of such glaciers during the 

 general dissolution of the ice sheet might bring them again into vigor- 

 ous action. Such recrudescence would at least help to explain such 

 phenomena as call for advancing ice. The coincidence of the direction 

 of stria? in the mountain valleys with the slopes of the surface, and the 

 independence of striae with reference to slopes elsewhere, does not 

 seem to the writer strong evidence of an independent ice epoch during 

 which the ice was largely confined to the valleys. It is believed that 

 existing stria? were very often, if not very generally, made by the later 

 phases of ice movement in the regions where they occur. It seems 

 rational to believe that while Scotland was covered with ice to great 

 depths, the movement of the same was largely independent of topogra- 

 phy ; but that later, when the ice was undergoing dissolution, when 

 the highlands had become bare, and when the valleys were still 

 occupied by ice, its motion was in correspondence with the local 

 slopes. Such stria? as were developed at that time would necessarily 

 be in harmony with the direction of the valleys. It is believed that 

 a re-advance might take place sufficient in vigor to explain the phe- 

 nomena cited from Scotland, without being of sufficient extent, or of 

 sufficient importance from other points of view, to be regarded as a 

 distinct glacial epoch. If, on the strength of the evidence presented, 

 we are not altogether convinced that the third glacial epoch represented 

 in Scotland (the fourth of the full series) was sufficiently distinct from 

 its predecessor to be ranked as a distinct epoch, as we have been accus- 

 tomed to use that term, it does net follow that new evidence may not yet 



