I860.] JAMESON DRIFT, ABERDEENSHIRE. 351 



as we do not see on any present coast-line ; and also from its uniform 

 increase towards the mouths of valleys. 



Fourth. From the absence of marine fossils. 



In examining the course of many rivers in connexion with this 

 subject, I observed that where the valley was narrowed by the ap- 

 proach of the enclosing hills, so as to form a gorge, pass, or ravine, 

 the sides of such ridges were denuded of all drift to a most remark- 

 able degree, and in a manner that seemed to me inexplicable by 

 any mere river-action however prolonged ; for this denudation fre- 

 quently ascends many hundred feet, sometimes even a thousand 

 feet and more above the present bed of the stream, and has imparted 

 a bare, stony, washed aspect not visible on the other sides of the hills 

 even where the slope was of equal steepness. Such appearances are 



Fig. 4. — Section across the Valley of the Tay at Birnam, showing the 

 excavation of the Drift. Distance 2^ miles. 



W. Hill of Newtyle E. 



Birnam Hill. The Tay. (1047 ft.). 



seen on the Tay at the Pass of Birnam, where the west side of the 

 Hill of Newtyle has its rocky strata laid bare all the way up to the 

 summit, which is about 900 feet higher than the river at that place. 

 The denuding agent has in this case evidently flowed over the crest 

 of the hill ; for the rock at the top, which is of a coarse clay-slate, 

 sticks out in lumpy knobs, the intermediate spaces between which 

 have been swept clean of all small debris ; while the opposite flank of 

 the Hill of Birnam has been bared of earthy cover to similar heights. 

 The Hill of Craig-y-bams, at the north side of Dunkcld, is also re- 

 markably denuded even to its summit, which is about 1150 feet high. 

 I met with no polish nor striae on these rocks indicating glacier-action 

 as the cause of this remarkable denudation, although the texture of 

 these masses seemed eminently adapted in many rases for taking and 

 retaining such markings. 



What is farther interesting in this locality is a long hollow stretch- 

 ing from Blair Qowrie towards Dunkcld, and terminating at the 

 Loch of the Lows near the latter town. Now 1 found by aneroid 

 measurement that the summit-level of the road, where it crosses the 

 watershed between this loch and the Tay, is about 302 feet higher 

 than that river at Dunkeld Bridge. This watershed also presents 

 great signs of denudation, consisting of masses of rugged gneiss 

 scoured bare of all drift and de*bris; and the face of the hill t«» the 

 north has also a very bare, washed appearance. 



Sir Charles Lyell, writing of this locality in L840 (see Proceed- 

 ings of Geol. Soc. vol. iii. p. 342), mentions that a continuous stream. 



