The Glacial Theory. 



151 



three terraces, on the two sides of the Glen Spean near the Bridge 

 of Roy, will likewise be understood from this explanation. The sup- 

 position now made is confirmed by a fact which there is no other mode 

 of accounting for; viz. that the bottom of Glen Spean in front of Loch 

 Treig is not only polished with that polish characteristic of glaciers, 

 but is moreover scratched transversely, that is to say, at right angles 

 to the direction of the valley, by a cause which evidently proceeded 

 from Loch Treig. I do not believe that a locality exists, where the 

 facts indicate, in a more special manner, the cause which has pro- 

 duced them. The horizontal terrace of Glen Gloy is susceptible of 

 a very natural explanation by a glacier issuing from the valley of 

 Loch Arkeig, crossing Loch Lochy, and damming up Glen Gloy 

 above Low Bridge. This supposition would also clear up the differ- 

 ence of level between the terraces of Glen Gloy and those of Glen 

 Roy, and would obviate the necessity of imagining soulevemens of the 

 neighbouring valleys, which communicate in the same manner with 

 the ocean, and do not nevertheless exhibit any trace of terraces. 



In following up these facts in all their variety, we are easily en- 

 abled to explain the numerous terraces which we meet with in Scot- 

 land, by supposing barriers of ice at the mouths of the valleys ; 

 whether it was that the lateral valleys closed them by their glaciers, 

 as at the Bridge of Roy, or that the waters of the sea, by heaping up 

 ice on the coasts, offered a temporary obstacle to the running off of 

 the waters of the land, or intercepted large sheets of salt water. The 

 presence of an Arctic fauna, in the deposits superior to the till, 

 which might be formed in these creeks of the sea, would thus pre- 

 sent nothing but what is quite natural.* 



Movement of Glaciers. — To ascertain this and several 

 other points connected with the structure and effects of re- 

 cent glaciers, which it became necessary to know, in order to 

 appreciate the effects in the appearances we have describ- 

 ed, MM. Agassiz, Guyot, Forbes, De Charpentier, Desor, 

 Heath, and others visited the glaciers of the Bernese, Ober- 

 land, on various occasions in the spring and autumn. One 

 of the first objects of these visits was, to ascertain the sound- 



* Op. Cit. p. 237, 



