S. V. Wood, j an. — American and British Surface- Geology. 543 
probably terminated direct in the sea, but on its eastern side it was, 
as presently described, divided from the sea during part of the Upper 
Glacial period by a beit of land formed of the eastern parts of 
Essex, Suffolk, and Norfolk. To the action of this glacier, when, 
during its greatest extension, its principal mass rested on the great 
Fen level, do I attribute the formation of that level itself ; its edges 
as above defined being on all sides, except the north, within twenty 
iniles of the Fen boundary ; and to the extrusion of its moraine 
during recession do I refer the principal part of the chalky clay, the 
rest having been accumulated by droppings in mass from ice which 
floated in the sea during its greatest extension, as well as in the sea 
that followed up its recession. As explained subsequently, a branch 
from this glacier passing through the gorge of the Humber carried 
out into Holderness nearly all the moraine engendered north of that 
gorge, as well that engendered for a few miles south of it, the ice 
against the Wold scarp drawing in from both sides of this gorge 
to form a tongue which issued through the valley of the Humber. 
Thus, as the glacier receded northwards, the moraine extruded be- 
came less and less, so that before it receded to the latitude of the 
Humber it had shrunk away from the Chalk Wold on its Western 
side, and there was no more chalky moraine to extrude. North 
of Holderness, however, the glacier which came through the Yale 
of Pickering, and passed over the lower ranges of the Wold for a 
few miles inland of Flamborough, to which I have already adverted 
as giving off bergs during the accumulation of the Contorted Drift, 
but which, after the termination of that accumulation, ceased to give 
off bergs, and which also had wasted back under the influences 
which caused the Lincolnshire glacier to waste back and disappear, 
still brought chalk debris, derived from the north scarp of the Wold, 
but accompanied at first by a corresponding abuudance of the hard 
rocks which lie north of the Wold, and form the opposite side of the 
Pickering trough . 1 This morainic material is of a dark purple 
colour in its lower part, changing to a more reddish purple upwards. 
In its lower part it is full of rolled chalk mixed with the more 
angular debris of hard rocks, and at its junction with the lead- 
coloured chalky clay at its base ( a of the sections and map) sheets 
of it frequently alternate with sheets of the latter, showing, it seems 
to me, that from this horizon at least upwards the clay of Southern 
Holderness originated from the dropping process. and other forms 
of marine deposit, and not by direct moraine extrusion. As we see 
the succession upwards, exposed in the high cliff of Dimlington, and 
1 This trough is that lying hetween the north scarp of the Chalk Wold and the 
slope of the Eastern Moorlands formed mostly of rocky Jurassic heds. Its eastern 
end is now blocked up by the last of the morainic clay which its glacier engendered, 
so that the drainage flows in the opposite direetion to that in which the moraine 
travelled to the sea, viz. westwards and roimd the north-west angle of the Wold, and 
thence southwards to the Humber, west of the Wold scarp. During the Contorted 
Drift the Pickering glacier, I conceive, travelled perhaps 50 miles on hoth its sides 
over chalk ; but at the period of the commencement of the purple clay it had shrunk 
back so that one side only touched the chalk, and this for a few miles only, and as 
the purple clay deposit proceeded, it gradually shrank from the chalk altogetlier. 
