A SUMMER RAMBLE AMONG THE HEBRIDES. 123 



gray band of from three to six feet, and is succeeded by a si- 

 milar gray band in turn. The ripple-marks I found as sharply 

 relieved in some of the folds as if the wavy undulations to 

 which they owed their origin had passed over them within 

 the hour. The comparatively small size of their alternating 

 ridges and furrows give evidence that the waters beneath which 

 they had formed had been of no very profound depth. In 

 the upper part of the valley, which is bare, trackless, and 

 solitary, with a high monotonous sandstone ridge bounding it 

 on the one side, and a line of gloomy trap-hills rising over it 

 on the other, the edges of the strata, where they protrude 

 through the mingled heath and moss, exhibit the mysterious 

 scratchings and polishings now so generally connected with 

 the glacial theory of Agassiz. The scratchings run in nearly 

 the line of the valley, which exhibits no trace of moraines ; 

 and they seem to have been produced rather by the operation 

 of those extensively developed causes, whatever their nature, 

 that have at once left their mark on the sides and summits 

 of some of our highest hills, and the rocks and boulders 

 of some of our most extended plains, than by the agency of 

 forces limited to the locality. They testify, Agassiz would 

 perhaps say, not regarding the existence of some local glacier 

 that descended from the higher grounds into the valley, but 

 respecting the existence of the great polar glacier. I felt, 

 however, in this bleak and solitary hollow, with the grooved 

 and polished platforms at my feet, stretching away amid the 

 heath, like flat tombstones in a graveyard, that I had arrived 

 at one geologic inscription to which I still wanted the key. 

 The vesicular structure of the traps on the one hand, identi- 

 cal with that of so many of our modern lavas, the ripple- 

 markings of the arenaceous beds on the other, indistinguish- 

 able from those of the sea-banks on our coasts, the upturned 

 strata and the overlying trap, told all their several stories 

 of fire, or wave, or terrible convulsion, and told them simply 



