1878.] Superficial Gravels and Clays. 339 
the northern watershed, more than 300 feet above the sea. 
Yet from the neighbourhood of Ely, southward, not a trace of 
the passage of this immense mass of ice has been recorded 
in the eastern counties, although the boulder-clay generally 
overlies loose beds of sand and clay. That in some parts 
glacier ice might have passed over small areas under peculiar 
circumstances, and melted off again, without leaving any 
mark on the beds below, seems probable enough ; but the 
distance from Ely to Finchley is about 60 miles in a direct 
line, and that a glacier of that length, and of sufficient 
thickness to over-ride the watershed of the Thames Valley, 
should have left behind it no trace of its passage, nor any 
of the moraines that mark the line of retreat of other 
glaciers, is a theory that cannot at present be accepted, 
notwithstanding the faith of its talented author in its 
efficiency. 
With the theory of floating ice— by which is meant both 
that of coast ice forming during the winter, breaking up in 
the spring, and carrying away from the shores and distri- 
buting materials frozen to it, and that of icebergs breaking 
off from the ends of glaciers terminating in water — the phe- 
nomena seem to be in entire accordance. Local rocks are 
scarce ; indeed nothing is more remarkable in the Upper 
Boulder-clay at Finchley than the absence of fragments from 
the underlying London Clay. The far-travelled stones are 
most abundant near the top of the ridge, where floating ice 
was likely to ground and deposit its freight. The stones are 
also scattered here and there through the deposit, as if 
dropped at different times during its formation. There are 
faint traces of lines of deposition in some of the exposures, 
and the general absence of stratification is not more marked 
than it is in the Upper Thames brick-clays, the formation of 
which is universally ascribed to deposition from water. 
The much greater abundance of transported stones on and 
near the ridge of the hill, and the gradual diminution in 
their numbers and size on the lower slopes until the clay at 
the bottom of the valley contains only a very few scattered 
pebbles, is the very opposite to what we should have ex- 
pected from the action of a glacier, and just what we should 
expert as the result of floating ice ; for the former gravitates 
to the bottom of the valley, and deposits there a great pro- 
portion of the stones it carries along, but the latter generally 
m confined waters leaves its burdens on the shores. Around 
the lakes, and at the heads of the fjords of Nova Scotia, 
there are lines of great stones left by the ice when it breaks 
up in the spring. Sir Roderick Murchison, in his description 
