Vol. 58. ] GLACIER-LAKES IN THE CLEVELAND HILLS, 489 
not, as Mr. Lamplugh thinks, to a local deformation, it proves a 
lower land-level at that period, not a higher. 
The blown-sand and landwash resting on the Sewerby beach do 
not necessarily imply even a temporary elevation, of however small 
an amount ; for, as the obstruction upon the eastern coast of Britain 
of the great Scandinavian ice-sheet would be exercised progressively 
from north to south, and it is probable that the Straits of Dover had 
not been opened at the beginning of the Glacial Period, the nar- 
rowing strait to the northward would admit so little tidal water 
that the North Sea would become practically tideless, and the highest 
beaches (namely the ‘ storm-beach’ and springtide beach) would be 
abandoned by the sea. I think it quite probable that the blown- 
sand and landwash of the Sewerby section represent this phase, 
which must have intervened between the abandonment of the beach 
and the onset of the ice that deposited the Basement Boulder-Clay. 
Briefly, the evidence of the Vale of Pickering and the Vale of York 
indicates a long period of pre-Glacial elevation ; while the evidence of 
the Sewerby beach and cliff, with the wide plain of marine denuda- 
tion which confronts them, shows very clearly that for a long period 
of time (pre-Glacial or early Glacial) the land-level was practically 
identical with that of to-day. 
How these apparently conflicting results are to be reconciled I 
cannot undertake to suggest, beyond saying that the different levels 
were probably successive. 
VI. GuactaL Deposits anD GLACIATION OF THE CLEVELAND AREA. 
The Glacial deposits which fringe the Jurassic hill-country of 
Yorkshire, and penetrate at a few points into the interior of the 
system, present few features special to the region, save in the matter 
of distribution and the nature of the included erratics. 
Most writers on the subject have recognized a threefold division 
of the Drift, namely :— 
Upper Boulder-Clay ; 
Middie Sands and Gravels ; and 
Lower Boulder-Clay. 
Few sections exist) which show the three divisions superposed, 
and it appears to be mainly by its relation to a bed of sand or 
gravel—-assumed to be the middle member of the series—that a mass 
of Boulder-Clay can be pronounced to belong to the Upper or Lower. 
In the Geological Survey Memoir on the country round North- 
allerton, Mr. Fox-Strangways speaks of the ‘reddish Upper 
Boulder-Clay, and later of the ‘ Boulder-Clay,’ maintaining 
throughout this region ‘its usual character of a stiff clay having a 
dark colour when unweathered.’ He further remarks that ‘ foreign 
rocks occur principally in the lower Boulder-Clay, the upper clay 
is almost stoneless.’ It may be gathered from this, that there are 
two beds of Boulder-Clay—a lower, which is blue, and contains 
many boulders; and an upper Boulder-Clay, which is red, and 
