362 Royal Society. 



win, Esq., M.A., F.R.S,, Sec. Geological Society, was resumed and 

 concluded. 



The author premises a brief description of the parallel roads, 

 shelves, or lines, as tliey have been indefinitely called, which are 

 most conspicuous in Glen Roy and the neighbouring valleys, re- 

 ferring for more detailed accounts to those given by Sir Thomas 

 Lauder Dick, in the Transactions of the Royal Society of Edin- 

 burgh, and by Dr. Macculloch in those of the Geological Society of 

 London. Both these geologists endeavour to explain the formation 

 of these shelves on the hypothesis of their resulting from depositions 

 at the margin of lakes, which had formerly existed at those levels. 

 The author, however, shows that this hypothesis is inadmissible, 

 from the insuperable difficulties opposed to any conceivable mode of 

 the construction and removal, at successive periods, of several bar- 

 riers of immense size, whether placed at the mouths of the separate 

 glens, or at more distant points. He does not, however, propose 

 the alternative, that the beaches, if not deposited by lakes, must of 

 necessity have been formed by channels of the sea, because he deems 

 it more satisfactory to prove, from independent phenomena, that a 

 sheet of water, gradually subsiding from the height of the upper 

 shelves to the present level of the sea, occupied for long periods not 

 only the glens of Lochaber, but the greater number, if not all the 

 valleys of that part of Scotland ; and that this water must have been 

 that of the sea. It is argued by the author, that the fluctuating ele- 

 ment must have been the land, from the ascertained fact of the land 

 rising in one part, and at the same time sinking in another ; and 

 therefore, that this change of level in Scotland, attested as it is by 

 marine remains being found at considerable heights both on the 

 eastern and western coasts, implies the elevation of the land, and 

 not the subsidence of the surrounding waters. The author next 

 shows, that in all prolonged upward movements of this kind, it might 

 be predicted, both from the analogy of volcanic action, and from 

 the occurrence of lines of escarpment rising one above the other 

 in certain regions, that in the action of the subterranean im- 

 pulses there would be intervals of rest. On the hypothesis that the 

 land was subjected to these conditions, it appears that its surface 

 would have been modeled in a manner exactly similar, even in its 

 minute details, to the existing structure of the valleys in Lochaber. 

 Considering that he has thus established his theory, the author pro- 

 ceeds to remove the objections which might be urged against its 

 truth, derived from the non-extension of the shelves, and the ab- 

 sence of organic remains at great altitudes. He then shows how 

 various details respecting the structure of the glens of Lochaber, 

 such as the extent of corrosion of the solid rock, the quantity of 

 shingle, the numerous levels at which water must have remained, 

 the forms of the heads of the valley, where the streams divide, and 

 especially their relation with the shelves, and the succession of ter- 

 races near the mouth of Glen Spean, are all explicable on the suppo- 

 sition that the valleys had become occupied by arms of a sea which 

 had been subject to tides, and which had gradually subsided during 



