On the Shelves of Lochaber. 9 



let us carefully attend to a most important iKculiarifi/ con- 

 nected with tlie Lochaber glens, and which suggested the 

 theory to which I have been so long attached. It will be ob- 

 served, on inspecting the map, that Glen-Gluoy opens into 

 the Great Glen, its streams flowing into Loch-Lochy. Glen- 

 Roy, including its offsets, opens into Glcn-Spean, and the 

 latter opens towards the Great Glen. 



The next fact to be kept in view is, that the Great Glen is 

 at a right angle with the direction of the flood, being NE. 

 and SW., the flood having passed from NW. to SE. 



Let us n6w suppose the flood passing over the land. As 

 soon as it subsided below the mountain tops, it would neces- 

 sarily be divided into currents and eddies, taking courses in- 

 to Avhich the water Avould be forced by the opposing eleva- 

 tions ; and this circumstance should be kept in mind, when 

 the forms and position of drift matter are contemplated. 

 AMien the waters had subsided a little below the summit level 

 between Glen-Gluoy and Glen-Roy (1, on map, Plate I.), the 

 former would become, not precisely a lake, but an arm of 

 the waters, protected on all sides from violent agitation, and 

 in a condition to form the upper shelf, No. 1. which we And 

 coincident with the summit level. While the waters flowed 

 over this level into Glen-Roy, no shelf could have been form- 

 ed on account of the violence with which the water advanced. 



The waters continuing to subside, as soon as the summit 

 level between Glen-Roy and tlie valley of the Spey (2.) be- 

 came exposed, this glen would become an extensive, and well 

 protected arm of the waters ; and, accordingly, we find No. 

 2 formed a very little way below the second summit level. 

 I may here remark that the shelves should be found to ter- 

 minate near to the locality where it would appear the waters 

 continued to be greatly agitated ; and this is seen to be the 

 case. 



Mr Milne, during his active researches, discovered a sum- 

 rait-level between the head of Glen-Glaster (3.), (a glen over- 

 looked by former observers,) and Glen-Spean ; and shelf No. 

 3, which had been a stumbling-block, is now found in cir- 

 cumstances precisely similar to those above it, in relation to 

 the summit-level. 



