274 PEOCEEDLNGS OE THE GEOLOGICAL SOCIETY. [Feb. 26, 



In the largest of a system of valleys many hundred feet deep and 

 whose sides are very steep, there occur three lines of terraces at dif- 

 ferent heights, each apparently preserving its horizontality over an 

 extent of above twenty miles. 



The sight of these extensive j)arallel lines immediately suggests 

 the idea either, 



1st, that they had arisen from the beaches of ancient lakes which 

 had formerly fiUed the intervening valleys, and that the levels of 

 those lakes had at distant intervals been reduced by the bursting of 

 successive barriers by which their waters had been confined ; or 



2ndly, that they had formed the beaches of a system of fiords, 

 or narrow inlets of the sea, which had been elevated at various times 

 by internal heat. 



The first of these suppositions is, I believe, most generally 

 adopted ; and it appears to me to be the most probable. 



These parallel roads themselves slope gently inwards towards the 

 central valley. They are about 50 feet broad, and consist of the 

 same angular fi^agments of stone as those which rest upon the 

 slopes above them. No one who has seen them can doubt that they 

 are the result of water-levels ; and the bursting of successive bar- 

 riers seems to be the most probable cause of their existence. 



But the difficulty still remains of accounting for the origin of 

 such beaches resting upon the sloping sides of very steep mountains 

 and themselves covered with fragments of the rock on which they 

 repose. 



"WTien these valleys were occupied by water, the lakes were not 

 sufficiently large to allow of the formation of a beach by the action 

 of their waves. 



If such lakes had existed in a climate in which their ivaters luere 

 never frozen, the rain which poured upon the ujDper part of the sur- 

 rounding mountains might certainly in a long course of years have 

 washed down their sides a multitude of the fragments similar to 

 those now lying upon their steeply inclined surface. The winds also 

 would have contributed to this transfer of the loose stones from the 

 higher and more exposed portions of the mountain to lower levels. 

 Under such circumstances the detached stones, notwithstanding 

 occasional impediments, would descend with a continually increasing 

 velocity. On reaching the surface of the water they would plunge 

 obliquely into it, still advancing until, their horizontal velocity being 

 destroyed by its resistance, they would fall vertically to the bottom. 



If such lakes had existed in a climate in which they luere occa- 

 sioimlly frozen, hut hi ivJiich no snoiu fell, then the oblique impact 

 of the stones detached by the wind or rain would cause them to re- 

 bound from the surface of the ice, and advance by a series of bounds 

 far beyond the margin of the lake. 



If such lakes were situated in a climate in which the mountains 

 ahove them as well as the lakes themselves were occasionally covered 

 with snow, then the slow melting of the snow upon the upper 

 parts of the mountains would lubricate their siu'face. The snow 

 itself would gradually subside, carrpng with it many of the loose 



