166 Charles Maclaren, Esq., on Grooved and Striated Bocks 



Loch Long — Arrows 7 and 8. — I found grooves on the 

 beach, on the east side, at a hamlet called Letter, though the 

 coarse texture of the slate here is ill fitted to retain them. 

 They run parallel to the line of the loch. A friend of mine 

 saw others on the west side, a mile or two north of Holy 

 Loch. But the most conspicuous and characteristic are on a 

 vertical surface of rock on the west side, immediately below the 

 junction of Loch Goil with Loch Long They are horizontal, 

 from one to two inches broad, and cover some square yards. 

 When the rock is wet they are seen from the deck of the 

 Loch Goil steamer at the distance of 50 feet. Large grooves 

 of this kind, on a vertical surface (and the examples are not 

 rare), as they could only be produced by an immense lateral 

 pressure, acting at right angles to the force of gravity, seem 

 to me of themselves conclusive against the hypothesis which 

 ascribes their production to currents of water charged with 

 stones and gravel. 



The local position of these well-marked grooves seems to 

 illustrate an opinion lately put forth by Agassiz, Desoi% and 

 Charles Martins. They say it is necessary to the formation 

 of a glacier that a cavity {cirque, amphitheatre^ much wider 

 than itself should exist above it on the mountain, to serve as 

 a reservoir for the collection of the ice and snow which i'eed 

 it.* Now, Loch Goil meets Loch Long at an angle of about 

 40°, forming with it a figure resembling the letter Y. When 

 ice and snow filled both valleys to the depth of 1200 feet, 

 the comparatively low hill in the bifui'cation, called Argyle's 

 Bowling- Green, would be nearly covered, and the upper por- 

 tion of the valley would form a reservoir or mer de glace six 

 or seven miles wide, such as Agassiz describes. But taking 

 them in their present state, each of the lochs, before they 

 join, is as broad as the united loch after the junction ; and if 

 they were filled with ice moving slowly southwards, that ice 

 would be powerfully compressed when the united mass was 

 forced into a channel only half as broad as the two channels 



* Paper by Charles Martins, Edinburgh New Philosophical Journal, No. 

 Ixxxv., p. 54. 



