138 
up to the highest summits of the moors. It contains very- 
little limestone, generally speaking ; and that little, from the 
positions in which it is found, would appear to have been 
floated by ice. Nine-tenths of the yellow clay formation 
is local, and must have been principally washed out of 
the hill- sides where it is found, or carried downwards, or 
transversely to the direction of the valleys. At the bottoms 
of the valleys, as at Bingley, it graduates into well rounded 
boulder gravel. On the summits of the table-lands, up 
to the height of more than 1000 feet above the sea, it 
is as much a boulder- drift as in the valleys — >vith this 
difference, that the matrix of the boulders and pebbles is 
more sandy than at the lower levels. During the accumu- 
lation of this drift, the table-lands and moors must 
have been completely submerged. On Rombald's Moor, 
Harden Moor, and elsewhere, blocks and well-rounded 
pebbles of a fine light- coloured sandstone called calliard stone, 
may often be seen in abundance. I have particularly exa- 
mined those on Harden Moor, where, on the very summit 
the calliards lie on the millstone grit. Unless their presence 
can be accounted for by supposing them to be the wrecks of 
a formerly-existing calliard bed in situ (which several con- 
siderations render very improbable), or to have been floated 
by ice from the outcrop of calliard beds at a higher level on 
neighbouring moors, it is difficult to conceive how they could 
have been transported. About 150 feet lower down than 
those found on Harden Moor, there is a bed of calliard in situ. 
Land ice could not possibly have pushed up fragments from 
this bed without mingling them with debris collected during 
the preceding part of its course. But to those who are 
acquainted with what is now going on in the Baltic the 
supposition will not appear unlikely that these calliards may 
have been progressively moved up the hill side by stormy 
wave-action, combined with the action of coast-ice and ground 
