in the Mkldle Begiun of Scotland. 163 



island, bth, The cause assigned does not explain how boul- 

 ders weighing many tons were carried from the Grampians 

 across the centrcxl valley of Scotland, the bottom of which is 

 only 200 feet above the sea, and deposited on the Pent- 

 lands, at spots 800 feet higher. A current of water, how- 

 ever powerful, would have dropt them in the low country. 

 {5th, The debacle does not explain other distinct traces of the 

 action of water upon our hills. Mr Chambers, in his recent 

 work, has shewn that satisfactory evidence exists of the pre- 

 sence of the ocean in its pi'oper form of a horizontal sheet of 

 water, up to 1500 feet above its present level. Had this fact 

 been known, and carefully studied, Sir James Hall would 

 have been spai'ed the necessity of resorting to a great hypo- 

 thetical Atlantic wave. 



No agent yet known but ice, or ice conjunctly with water, 

 seems capable of explaining the phenomena for which Sir 

 James Hall called in the aid of a debacle. Those who have 

 read the excellent works of Professor Forbes and Professor 

 Agassiz, are aware that a glacier, during its slow progres- 

 sive motion, transports vast masses of rock over a distance 

 of many miles ; secondly, that it grooves and polishes the 

 bottom and sides of the valley containing it, by means of the 

 stones and gravel which it brings down ; and, thirdly, that 

 many of these stones are themselves grooved by the attrition 

 they have undergone in sliding over the lixed rocks. We 

 know also, that as floating ice lifts large stones from the bot- 

 tom and sides of rivers, or the shores of the sea, and carries 

 them away, it may leave striae on rocks over which it passes. 

 Mr Lyell found well-marked strise cut on a rock in the Bay 

 of Fundy, which he attributed, on good grounds, to the 

 packed ice of the preceding season, or of a period very little 

 farther back. The pack ice accumulates there to the depth 

 of fifteen feet.* If this was efi^ected on the shore by so small 

 a mass, it is easy to conceive that our plains might be grooved 

 and abraded by icebergs, armed at bottom with stones or 

 gravel, and floating in a sea 500 or 1000 feet deep. These 



* Travels in North Aiiifrica, 184.5. vol. ii., p. 173. 



