116 Lieut. -Colon el Portlock on the Scratching of Bocks 



of the operation, and by the nature of the substances. Their 

 depths vary according to circumstances, and they often de- 

 scend so far as to occupy the valleys beneath." " As these 

 appearances occur in very gentle declivities, as in Cumbray 

 and Isla, or almost on level ground, as near Comrie, here is 

 a demonstrated cause of even transportation which geology 

 has overlooked. That even boulders may have been gra- 

 dually moved in this manner to great distances from the 

 parent rock, is abundantly obvious ; and I may here say, 

 once for all, that whatever volumes may have been bestowed 

 on these travelled blocks, there is no reason for separating 

 them from the several classes of alluvia to which they be- 

 long," — an idea again identical with that of Mr Mallet. M. 

 Bausse, in his Essay on the Chaine des Rousses (1834), 

 describes the mountain gorge of Flumay, which is formed by 

 the junction of the granitic and gneisose rocks of the great 

 chain of the Rousses with the slate escarpment of Cote-Belle. 

 This deep ravine narrows at its bottom almost to a line, and 

 has there a steep descending slope. On the left, and to- 

 wards the head of the gorge, the gneisose beds, which are 

 above, have been greatly dislocated, and have produced huge 

 accumulations of debris at the bottom. On the right, " the 

 very bowels, as it were, of the mountain de Cote-Belle are 

 exhibited as the various beds crop out in the steep escarp- 

 ment. Strangely, indeed, is this escarpment ravined and 

 grooved and notched by the projecting of its several beds, 

 and shaped into rugged asperities and bold needles, which 

 are incessantly giving way and falling to the bottom. It is 

 here that we find torrents or coulees de debris^ which the 

 rains and great thaws have the power of moving. In this 

 passage, M. Dausse almost seems to have Mr Mallet's illus- 

 trative image of a glacier in his mind, but he contents him- 

 self with merely stating that huge accumulations of debris 

 are made to flow down the course of a steep ravine by the 

 increased power of water consequent on heavy rains or sud- 

 den thaws. 



Quotations of a similar character might be multiplied, as 

 the first mode of explaining the polishing and grooving of 

 rocks was naturally to ascribe them to the passage of drift — 



