486 
Proceedings of the Royal Society 
2. The gravel heaps consist of sand of different degrees of 
fineness, and of stones varying in size from small pebbles to such as 
are twice or thrice larger than the head. The coarse sand can he 
traced to the wear of the district rocks, hut there are beds of very 
fine sand, which seems to differ wholly from these. In the rare 
instances in which large boulders were met with in these heaps, 
there were suhangular specimens of rocks in the neighbourhood. 
The erratics occur on the heaps. 
3. Blocks abound high up the mountains, many of enormous size 
and weight, for whose position no explanation can he found in any 
of the forces at present active in the locality. 
4. The position of boulders in the plain may have as great 
significance to the glacialist as that of those high up the mountains. 
This was illustrated. If the position of that on the plain is one to 
which it could not have rolled, the face of the country being at the 
time of its deposit as it is now, the supposition is admissible that 
both the boulder on the high level and that on the low ground may 
have been dropped by an agent on which the inequalities of the 
surface could have no bearing. 
5. Both angular and round boulders occur together at high levels. 
6. Boulders are met with the same as the rocks in which they 
lie in heaps whose form and position no theory of weathering or 
of rolling can explain. 
7. In many places the striation is much hatched, and it is 
difficult to make out the initial direction. That the striae are very 
often in the line of the larger axis, and most frequently, by the 
compass, north-west and south-east, is almost all that can he said. 
Some large boulders present comparatively symmetrical grooving or 
striation over the whole surface. When this occurs above only, 
the readiest explanation is found in tracing it to the action of 
another boulder carried in the direction of the striaB. 
8. In ascending Ben Nevis, and when on the summit, most 
observers are struck with the great extent of the angular debris and 
the immense number of great cornered stones. Snow or ice 
gliding over this loose surface might, at first thought, he expected 
to sweep it all away. Even snow melting suddenly might he held 
likely to carry it down to the valleys. But the temperature which 
determines the formation and the fall of the snow determines also 
