376 
MORTIMER : SECTIONS OF DRIFT. 
chalk, and the chalk-gravel capping the cliffs contains hardly any 
but Yorkshire flint. Also in the clays below, even to the base of 
the cliffs, are transported masses of crushed and redeposited chalk, 
veiy variable in size ; but unlike the transported chalk near Eas- 
ington, they contain no foreign flint. 
Most probably the chalk gravels and masses of crushed chalk 
between Bridlington and Hornsea have been derived from the 
neighbourhood of Flambro' Head, having been removed and car- 
ried to the place they now occupy, by the stream of bergs from the 
northern ice sheet shearing against the Head. These ice rafts, 
after ploughing the bed of the ocean and pushing clayey matter be- 
fore them, probably became 6xed, and on the melting of the ice, the 
transported matter was dropped in patches and pockets of every 
shape and size ; being more or less rearranged by the ebb and 
flow of the tides, into every form of false bedding, as is so beauti- 
fully shown in Craike Hill, and many other similar mounds and 
ridges dotted throughout Holderness. The rebedding observed 
in these ridges, the 24 ft. of laminated marl clay under 12 ft. of 
boulder clay in the Poundsworth railway cutting, and the thin 
intercalated beds of a saDdy nature, shown in the accompanying 
sections, may be due to a somewhat mild interglacial period. This 
would seem to be indicated by the unstratified boulder clay , which 
has been observed to cap Craike 11 ill, and also to cover Kelsey 
Hill and several others of large size throughout Holderness, and 
which must have required very different conditions for its forma- 
tion. 
To avoid any necessity for a great change in the climate, and 
also a change in the relative height of land and sea at that time, 
we may suppose that the laminated marl and the thin patches of a 
sandy nature were formed and intercalated with the clays, by having 
been, in most cases, deposited in areas of still water enclosed be- 
tween stranded ice rafts. Lakes of various sizes might have been 
thus formed ; and frequently little pools would exist in the dissolv- 
ing bergs themselves, Afterwards other rock burdened rafts in 
