10 On the Shelves of Lochaber. 



The next summit-level (No 4.) is that which separates 

 Glen-Spean, and all the comparatively low country extend- 

 ing from the eastern side of Ben Nevis to the mountains 

 forming the glens in question, from Strathspey. When the 

 waters had subsided below this level, all this district would 

 be filled with water little agitated, except in the vicinity of 

 the Great Glen, through which the waters must have con- 

 tinued to flow both towards the NE. and SW. Accordingly, 

 wc find shelf No. 4. commencing at the summit-level, and 

 stretching towards the Great Glen, disappearing where Ave 

 may presume th.e waters were too much agitated to admit 

 the formation of a shelf. It should be observed that when- 

 ever the flow of water over a summit-level ceased, the sub- 

 sidence of the waters would be checked for a time, they hav- 

 ing to take a new and circuitous course, and thus ample time 

 would be afforded for the formation of a shelf. 



Mr Darwin has remai'ked the probability that the forma- 

 tion of the shelves was somehow connected with these sum- 

 mit-levels ; and it appears to me that there cannot be a doubt 

 of the fact, that the nature of the connection is as I have 

 stated. It is clearly more natural that the waters had sub- 

 sided to the levels, than that the land was raised from the 

 sea ; for, in the latter case, it would have been necessary to 

 lift the land to a certain point, and then stop until tlie first 

 shelf was formed ; then to lift it again rapidly that no formation 

 should take place during the interval, and to stop till the next 

 shelf was formed ; and so on — a process not likely to pre- 

 serve the levels. It must be remarked, too, that the shelves 

 are not shaped precisely as if the matter forming them had 

 been deposited by water in a state of absolute rest. Their 

 upper surfaces slope downwards, and the edges are rounded 

 off to the steeper slope, indicating the action of waves of con- 

 siderable power. 



We have now seen the effects of the peculiarities of the 

 locality of Lochaber on the waters of the great flood, forcing- 

 it to leave behind it traces of its action, having very marked 

 relations among themselves. These are altogether indepen- 

 dent of the effects of the flood in other localities (not having 

 similar peculiarities,) where we find the effects, as indicated 

 by the drift, to be precisely what we should expect from the 



