REPORTS ON EXCURSIONS. 277 



range of mountains, the highest in the country, was, like all the 

 other Highland hills, a vast feeding-ground for very large glaciers, 

 From the peculiar physiographical conditions of the district, an 

 immense accumulation of ice took place in Glen Spean and in the 

 Great Glen. During the coldest period the pressure from the south 

 and west was so great as actually to force the ice up Glen Roy 

 into Strath Spey, and so seaward. As the climate moderated, a 

 lake was formed in Glen Roy, but, as all southern outlets were 

 blocked by glaciers, the water could only escape at the head of the 

 valley, over the col, or dividing ridge, into Strath Spey. The height 

 of the col is 1,151 feet, while the uppermost road is 1,155 feet at 

 highest and 1,148 feet at lowest. When the ice had further 

 diminished in Glen Spean, so as to lea>ve free the col between 

 Glen Glaster (a side valley to Glen Roy), and the valley of the 

 Rough Burn, a tributary of the Spean, the water found an outlet 

 in this direction, and the second road was formed at a height of 

 1,077 feet at highest and 1,062 feet at lowest, that of the col 

 being 1,075 feet. The ice continued to shrink until Glen Spean 

 was nearly free, but the higher valleys and the Great Glen were 

 still full of it. The lake now occupied Glen Roy and Glen Spean, 

 escaping at the head of the latter through the pass of Makoul into 

 Strath Mashie, and thence into Strath Spey. The height of this 

 col is 848 feet; of the lowest road in Glen Roy, and the only 

 one in Glen Spean, 862 feet at its highest and 850 feet at its 

 lowest. 



With the farther amelioration of the climate the ice gradually 

 disappeared, and the drainage assumed its present flow. 



Survivals of the plant life of these arctic conditions are to be 

 found plentifully on the high hills to the south of Glen Spean, 

 but we saw none except Saxifraga aizoides, Linn. Other plants 

 observed were — Aspleniuin viride, Huds.j Fissidens adiantoides, 

 Hedw., Hylocomium triquetrum, B. tfe S., Hylocomium splendens, 

 B. k S. 



At Keppoch, ^n ancient seat of the MacDonalds, or Mac- 

 Donnells, of Keppoch, at the confluence of the Roy and the 

 Spean, are some fine trees. Two Larches were measured, and 

 found to have a girch of 13 feet 7 inches at 6 feet 7 inches, and 

 12 feet 8 inches at 5 feet respectively. These are the largest 

 trees of their kind yet seen at any of our excursions. 



