Geological Changes in the South of Scotland. 31 



is, as to ages, but not as to different epochs of geological time; 

 for as we have before stated, the scouring out of the valleys had 

 taken place previous to the deposition of the boulder clay, as is 

 clearly shown by the latter being less or more spread over the 

 former. But there is another consideration which we cannot 

 overlook ; the detritus seems all to have been driven in the same 

 direction, and locally the boulders are mostly all of the same 

 material . Again, it is so frequently interspersed with such huge 

 masses of rock as are never found in any of the older strata, 

 which gives strong ground for believing that those extraordi- 

 nary masses have been struck off the prominent rock, and borne 

 to a distance at a comparatively recent sera, by such a combi- 

 nation of powerful agents as more primaeval time does not ex- 

 hibit. At some places there is a well-marked distinction in the 

 mass, where the lower beds differ in colour, and are more or less 

 argillaceous than the superior ; the lower, likewise, rises with a 

 higher inclination towards the hills, while the incumbent beds 

 are generally of a lighter colour, and more arenaceous in com- 

 position. We can frequently detect small boulders of foreign 

 rock, such as sandstone, &c. of the coal districts, and various 

 rolled fragments of the trap family ; the first must have tra- 

 velled a great distance from the west, or north-west, while the 

 latter may belong to the numerous trap dykes which intersect 

 the district. These are chiefly to be found along the valleys, 

 but seldom upon the steep escarpments of the hills. We com- 

 monly observe that boulders of a large size are not so plenti- 

 fully interspersed in the clay, where it has evidently been 

 driven to a considerable distance, and where they do occur 

 they do not appear to have been rolled. At many places we 

 can scarcely pick out a boulder exceeding two or three lbs. 

 weight, the deposit being a homogeneous mass of clay and 

 small pebbles : in other places, where the debris has been 

 driven to a considerable distance, the boulders are exceedingly 

 well-rounded, while the opposite is the case with that resting 

 upon the escarpments of the hills, where fragments of all sizes 

 are seen indiscriminately mixed, with scarcely a rounded 

 angle. 



But in order to understand these remarks, it will be neces- 

 sary to examine the appearance of the hills, and describe 

 their various features downwards. It is not requisite to point 

 to the denuded summit of the hills with respect to this part 

 of the subject, for that those summits have been much denu- 

 ded is what none can deny, it being so striking and ob- 

 vious to all. While the denudation was going on, the grosser 

 debris would be forcibly driven over and rolled down the 

 sheltered side of the declivities, and the finer water-borne 



