159 
formerly filled with ice to a depth sufficient to bury the Isle 
of Man, or 2,000 ft. But I doubt whether the concliision of 
Professor Phillips follows from the facts. At the foot of a 
glacier the ice is of course less than, that depth, so that it would 
not there crush at its base ; and higher up the glacier, where 
the depth is sufficient to crush the base, the crushed ice could 
not escape since it would be confined by the uncrushed ice in 
front. It would, therefore, act like a fluid, and would assume 
the shape of the rocky basin. We may, perhaps, imagine 
that the crushed ice at the base of the glacier, might, in con- 
sequence of lateral pressure, crush its way through the icy 
barrier in front, and make its escape like water breaking 
down the banks of a reservoir ; but it is doubtful whether 
crushed ice would thus transmit pressure equally in all direc- 
tions. The most probable result would be that this barrier 
of ice, with its unfrozen stone, would be forced forward with 
all the pressure dammed up behind it, and would constitute 
an excavating tool of greater energy than any to be found in 
the present glaciers of the Alps. 
In an enclosed rocky basin the ice might certainly be of 
any depth. 
The paper was illustrated by numerous photographic views, shown with 
the oxy-hydrogen lantern. 
ON SILURIAN ERRATICS IN WHARFEDALE. BY J. R. DAKYNS, 
ESQ., M.A., r.G.S., OF H.M. GEOLOGICAL SURVEY. 
Some years ago I called attention, in a paper on the 
" Drift of the Yorkshire Uplands," read before the Geological 
Society of London, and in the pages of the "Geological 
Magazine," to the occurrence of Silurian Boulders in a part 
