Glaciers in Forfarshire. 201 



river cliff, consists of unstratified niud, full of boulders ; and the upper 

 part, from 50 to 100 feet thick, of gravel and sand, inferred by Mr Lyell, 

 from analogy, to be stratified. If tbis barrier be supposed to be a large 

 terminal moraine, accumulated by a retreating glacier, Mr Lyell states 

 that its origin is easy to be understood ; and that the water produced by 

 the melting of the ice may have overflowed the mound, and furrowed out 

 the softer materials composing the upper part into ridges and hillocks ; but, 

 he adds, it is difficult to comprehend how a capping of such materials on the 

 summit of a terminal moraine could have acquired a stratified structure. 

 At Cortachie, four miles below the barrier of Glenairn, the Esk enters the 

 lower country of old red sandstone; and a mile and a half farther down 

 it is joined by the Proson ; and a mile j'et lower, by the Carity. In the 

 district where these streams unite, there is a great amount of unstratified 

 detritus, full of Grampian boulders, and covered, for the most part, with 

 stratified gravel and sand, in some places from thirty to forty feet thick. 

 The phenomena exhibited by the till in that district, Mr Lyell conceives 

 might be well accounted for by the union of three or four large glaciers. 

 The author then proceeds to describe the phenomena presented by Strath- 

 more. This district is intersected by many longitudinal ridges, some 

 of which are 200 or 300 feet above the adjacent valleys. They are gene- 

 rally covered with till and erratics, derived partly from the Grampians, 

 and partly from the subjacent old red sandstone ; and the covering 

 is so prevalent in Strathmore, that the subdivisions of the rocks in situ 

 are difficult to trace. This boulder till, or mortar, as it is termed in For- 

 farshire, forms invariably the lowest part of the transported matter of the 

 Strath. Mr Blackadder has ascertained that it often fills hollows which 

 would become lakes or peat mosses if the till were extracted : and Mr 

 Lyell observes, that if the cold period came on slowly, the action of the 

 advancing glaciers would have pushed forward vast increasing masses of 

 detritus, and spread them over the Strath, filling up more or less the hol- 

 lows and cavities previously occupied by water. The Sidlaw Hills, the 

 highest point of which is 1500 feet above the sea, and the whole country 

 between Strathmore and the Tay, are overspread with an impervious 

 boulder formation. The erratics derived from the Grampians are equal in 

 size to those contained in the till of the glens and Strath, and are asso- 

 ciated with fragments of the subjacent grey beds of the old red sandstone. 

 One of the Grampian boulders, which lies within forty feet of the summit 

 of Pitscaulie Hill (700 feet above the sea), is a block of mica-slate thirteen 

 feet long by seven feet broad, and it is seven feet high above the ground. 

 The nearest point from which it could have been derived is fifteen miles to 

 the north-west. In conclusion, Mr Lyell observes, that though there are 

 evidences of glaciers having once existed in the principal highland valleys, 

 and their tributary glens in Forfarshire, and though the Scottish moun- 

 tains may have bccn^covercd with permanent ice, yet. that, in consequence 

 of the difference of latitude, Switzerland can present but an imperfect 

 analog)- of things in Scotland during the glacier period. It is, lie says, 



