270 
DAVIS : ERRATIC BOULDERS. 
which occupy all the rising ground for a distance of nearly a mile. 
The largest erratics are found in this direction, and altogether the 
force appears to have been greatest along this line. At the source 
of the boulders A, there are great masses of the grit, in part 
broken away and ready for transportation, just as so many masses 
had been carried before them ; and amongst these are a few large 
blocks of limestone, brought from a distance behind, and left by 
the ice on the gritstone surface. At the opposite extremity of the 
limestone plateau, its scarped edges are surmounted by numbers 
of the Silurian boulders, standing, when looked at from below, 
black against the sky, with the white horizontal beds of limestone 
beneath ; many Erratic blocks have fallen over this edge of the 
cliff, and lay scattered on the slopes below, and extend in gradually 
'diminishing numbers over the meadow lands in the direction of 
Austwick and Clapham, some of them on the site of a small lake 
which was drained only a few years ago. A number of the 
boulders have assumed picturesque forms, due partially to the 
weathering of their own surface, but more so that of the limestone 
underneath them. Occasionally a great block stands on a small 
pillar ; others are so balanced that they will rock and sway with a 
slight push, or are perched on the edge of the escarpment so that 
they appear almost incapable of resisting the action of a strong 
wind. 
A second stream which occupies the higher ground to the 
west, appears to have had its origin in several beds of Silurian 
rocks at B. Evidence of the intense pressure of the grinding 
mass of ice is afforded by the surface of the grits being broken 
into thousands of small pieces, along what seem to be lines of 
cleavage at right angles to the plains of bedding or deposition, 
here dipping about 45°- N. The ice which transported the blocks 
of gritstone along this side the valley has been forced along' the 
hill side, and towards F reached a height of 1200 feet; a much 
higher elevation than any other where boulders have been left by 
these glaciers. The Erratics are strewn for nearly a mile along the 
upper slopes of the hill side. The glacier bearing them entered 
