1851.] HOPKINS ERRATIC BLOCKS OF THE S. HIGHLANDS. 27 



many hundred feet above the present sea-level, as must likevrise^the 

 blocks which have proceeded from that mountain to the south into 

 Glencroe. Again, the blocks of white granite, which have passed 

 down from Loch Sloy to Loch Lomond, must have descended from 

 a still greater height. I have no means of ascertaining these heights, 

 except by a rude estimate ; but I should think they may amount to 

 1500 or 2000 feet. The blocks from Ben Cruachan also, in the 

 valley of Glenray, must have descended from an elevation of several 

 hundred feet. 



From what I have stated in the previous section, it would not 

 appear that we have any certain evidence that the depression of the 

 land below its present level, during the drift period, ever amounted to 

 2000 or even 1500 feet, either in this or the surrounding districts. 

 Still it must have approached the latter amount ; nor is there any 

 evidence of its not having been considerably greater. In Wales, too, 

 there appears to be distinct evidence of its having exceeded 2000 feet. 

 We can derive, therefore, from these considerations no positive proof 

 of the former action of glaciers. If, however, we regard the distri- 

 bution of the blocks along the sides of some of the principal valleys 

 in which they exist as indicative of the relative height of the sea at 

 the time of their transport, we obtain a presumptive proof that the 

 blocks were brought down to that level by glaciers. To this may be 

 added the direct indications of the former existence of glaciers. They 

 are not, however, either very numerous or very striking in this region, 

 although several instances of polished and striated rocks have been 

 described by Mr. Maclaren and other observers. They are chiefly 

 at comparatively low levels, and may perhaps, in some cases, be 

 rather attributable to half-floating ice driven forward by currents, or 

 other causes, than to glaciers properly so called. 



There are indications of glaciers, however, at much higher levels. 

 I have already mentioned the valley which descends from Loch Sloy 

 along the western flank of Ben Voirlich. . It afterwards turns suddenly 

 eastward, at the foot of the same mountain, down to Loch Lomond. 

 Immediately to the south of the point where the valley thus changes 

 its direction, the general surface of the rocks is much more rounded 

 than elsewhere, assuming the aspect which might be given to it by 

 the passage of a large glacier over it. The locality would be favour- 

 able for the formation of such a glacier, which would be fed by one 

 descending down the valley from Loch Sloy, and another from the 

 valley running up into the recesses of Ben Nime, besides minor 

 affluents. It would then descend partly down to Loch Lomond, and 

 partly down to Loch Long, along the valley already described as that 

 by which the blocks have reached the head of the latter loch. I 

 could find, however, no striae, nor, in fact, did I observe any surfaces 

 apparently calculated to preserve them. The only other direct in- 

 dication of glaciers which I remarked in this locality consisted in a 

 block, which was not granitic, reposing on a surface of granite. It 

 probably weighed twenty or thirty tons, and was split v^ertically in 

 the manner in which large blocks deposited by glaciers are frequently 

 divided. I may also mention, that in the valley of Glenray, and not 



