in the Middle Begion of Scotland. 179 



Much remains yet to be done before adequate materials 

 for a satisfactory theory are collected. In the mean time, a 

 few conjectures may be indulged in provisionally. 



The transportation of a block of mica slate, weighing 8 

 or 10 tons, from the Grampians, across the low land, to a 

 point in the Pentlands 1000 feet above the sea, is scarcely 

 susceptible of explanation, except by calling in the agency 

 of ice floating on an ocean at a far higher level than the pre- 

 sent. The existence of such an ocean, with masses of ice 

 floating on it, whether in the shape of icebergs, field-ice, or 

 coast-ice, being admitted, it seems a legitimate inference, 

 that the ice, boi'ne eastward by a current, and having pro- 

 bably stones and gravel adhering to it, or imbedded in it, 

 might produce the striae on the top of Torduff" Hill, arrow 

 24, and those at the other high localities 25 and 26. Far- 

 ther, as the ocean, in ascending to its higher position, or de- 

 scending from it, must have assumed different levels in suc- 

 cession, the striae on Arthur Seat, and Corstorphine and 

 Ravelstone Hills, and at all the other localities, high and 

 low, from Stirling to Gosford and Fenton Tower, might be 

 the result of the same agency. This seems a more reason- 

 able hypothesis than that which assumes, that a vast sheet 

 of ice covered the country from the Grampians to the Lam- 

 mermuirs (a breadth of 50 miles), and, in moving eastward, 

 grooved both the high lands and the low. It seems to afford 

 a better explanation of the phenomena. 



The craig- and-tail form is so often accompanied with groov- 

 ings, that it is due probably, in a greater degree, to floating 

 masses of ice than to the current which bore them along. 



There is a class of phenomena best accounted for by the 

 agency of coast-ice, which is well known to lift stones and 

 gravel from the bottom and sides of rivers and bays, and 

 transport them over moderate distances. Mr Lyell cites ex- 

 amples of blocks weighing 50 tons, being removed in this 

 manner by the ice of the St Lawrence. In this way we may 

 explain such facts as tlie following. 1. Thousands of gra- 

 nite blocks lifted from the hill in Glen Spean (arrow 1), near 

 Loch Laggan, and carried westward ; a vast number of them 

 dropped within a fui'long or half a mile of their oi'iginal site, 

 a smaller number conveyed a mile, and a few to much gi'eater 



