362 
PROCEEDINGS, 1871 — 1877. 
on the physical properties of ice in conuection with tlio glacial period. 
He briefly called attention to the fact that water expands in freezing no 
less than nine per cent. Ice, subject to great pressure, is melted at 
a considerably lower temperature than freezing point. This remarkable 
property goes far to explain how a mass of glacial ice can behave 
like a viscous body. If the bed of the glacier were smooth, and it 
could move without fi-iction, it would simply slide down by its own 
weight ; but the bed not being smooth, but offering projections of 
rock, the pressure exerted by these obstacles on the ice would be very 
great. The ice cannot yield like a viscous body, but it can melt, and 
this comes to much the same thing. The water which has been formed 
by this pressure shifts its position, and thus pressure is removed ; 
being again subject to the cold it is re-frozen, but a considerable 
proportion escapes through crevasses and other cracks in the ice, 
and forms a stream which issues from the foot of the glacier. 
Mr. J. R. Dakyns, of H.M. Geological Survey, described some 
Silurian erratics which he had found in Wharfedale. Wharfedale 
consists of two distinct portions, one extending from its source to 
the southern edge of Grass Wood, in which the river runs in a narrow 
valley. From Grass Wood to Beamsley, the river is bounded on the 
east side by Fells, but on the west it is an open drift-covered country, 
stretching away westward beyond the river Ribble. Below Beamsley, 
the river again flows in a narrow dale to Otley. In the lower part, 
only carboniferous series exist, and no other rocks are found in the 
drift as boulders. Between Beamsley and Cliapelhouse, Silurian 
erratics are plentiful, they have being largely cleared off the land 
and used as "throughs" in the walls. Mr. Dakyns considered that 
the explanation of the occurrence of these Silurian erratics is to be 
found in the occurrence beneath the mountain limestone of Silurian 
beds probably in the neighbourhood of Kihisey Crag. At the foot of 
the crag some strong springs are thrown out, which he considered as 
evidence of the presence of the Silurian rocks. The whole of the 
valley bottom is covered by an artificial detritus, and beneath this, 
though unseen, it is possible that the Silurian rocks exist from which 
the boulders were obtained now found in the lower part of the valley. 
A paper w^as read by Mr. Walter Rowley, O.E., on Deep Mining, 
