DAVIS: ERRATIC BOULDERS. 
273 
the Silurian rocks exposed in its lowest part were torn away from 
their beds and carried up the slopes of Norber and redeposited in 
many instances 200 or 300 feet above their original position. The 
Silurian rocks form a series of anticlinals along the valley ; these 
exhibit very clearly the action of the ice. They have a rounded 
smooth surface very different to the sharp angular blocks which 
have been transported by the ice. In some instances where the 
stone has been preserved from the weather, beautifully striated 
surfaces may be found. Such a one occurs about a hundred and 
fifty yards north of the bed of thick grit which supplied the 
principal stream of boulders. The scratches on the grit are deep 
and well preserved ; they point directly south to the part marked 
A on the map. The weight of the superincumbent ice and the force 
it exercised in tearing away block after block of the grits, very 
many tons in weight, often 20 to 30 feet in greatest diameter, and 
carrying them up the opposite hill, is truly astounding. 
In conclusion, the multitudinous aggregation of Erratic 
boulders at Norber, and their large size, required for their trans- 
port an agent of great power and irresistable force. This could 
not have been supplied by a small local glacier, but the gTeat ice- 
sheet descending from the north, filling up all the valleys, ^reach- 
ing far up the sides of the highest mountains, and enveloping the 
whole country in its icy pall to a height of hundreds of feet, is an 
agent sufficiently powerful to explain all the phenomena under con- 
sideration. Descending from the high limestone plateaux of Ingle - 
borough into the Crummack valley, the rough edges of the con- 
torted Silurian rocks were smoothed, polished, and rounded, and 
their surfaces scratched by the ice during it passage. A little 
further south the jointed masses of the Silurian grits were torn 
from their beds, and carried and pushed forward up the opposite 
hill to Norber, and beyond its extent far into the valleys round 
Clapham. Eventually the glaciers retreated, and left the boulders 
scattered in every direction, high on the hill sides to the west- 
wards, covering the limestone slopes of Norber, and extending 
far to the southwards over the lower ground beyond its escarpment. 
