S. V. Wood,jun. — American and British Surface- Geolog y. 545 
Chalk debris, immediately underlies the Hessle clay wrapper in tbe 
two bigh cliffs already mentioned ; wliile tbat of Scotland, so far as 
it belongs to the sarne period of glaciation, is latest of all, and may 
have accumulated while the South of England was the theatre of the 
disturbances presently referred to. Moreover, when the latest part 
of the Upper Glacial formation, the Moel Tryfaen and Lancashire 
high-level sands, was accumulated, it is clear that, except to the 
exteut possibly of some glaciers still remaining in the valleys of 
the islands to which the mountain district of the North of England 
was at that time reduced by submergence, there could have beeil 
no ice enveloping the Southern extremity of that district, though 
Snowdon and other higher mountains of North Wales may possibly 
still have been snow-clad. The North of Scotland, too, from its 
latitude, may also at this time have not been freed from its ice, so 
that the morainic clay of that part of Britain, except so far as it may 
be of later (i.e. Hessle) age, may even be synchronous with these 
high-level sands of Lancashire and Wales, for the shells which have 
occurred at Elie and elsewhere on its eastern coast, though more 
Arctic in character, possess the same modern facies as do those of 
Moel Tryfaen, and of Macclesfield, as well as those from gravels of 
Hessle age. 
In the Eastof England the sea, during that earlier part of the Glacial 
period to which the Contorted Drift belongs, was evidently deep enough 
to buoy up the glacier which occupied some part of the Chalk country, 
and break off portions into bergs ; and these, from the dimensions 
of the masses of reconstructed Chalk which by their grounding 
they introduced into the mud of that drift, must have been of con- 
siderable size. What that depth of water was it is difficult to 
estimate ; but when we consider that the mass of Lower Glacial 
deposits in which these bergs grounded was itself in that part near 
200 feet thick, it is clear that at this stage in the Glacial period 
the Eastern counties must have undergone, since the time of the 
newest Crag beds, great depression and submergence. As already 
mentioned, however, this sea-bed had, prior to the Middle Glacial 
sands, undergone denudation, the effect of which was to excavate 
along the lines of our present valleys wide and deep troughs, in 
which to a great extent these sands accumulated, and were over- 
spread in their turn by a deposit of the morainic chalky clay. 
After this, as I shall presently endeavour to show, so much of this 
area as forms the eastern part of the counties of Norfolk and 
Suffolk was early in the formation of the chalky portion of the 
Upper Glacial converted into a beit of land, which divided the 
inland-ice from the sea, and through the valleys of which that ice 
in the form of glacier tongues escaped. By the well at Yarmouth, 
described by Mr. Prestwich in the 16th vol. of the Journ. of the 
Geol. Soc. of London (p. 450), we leam that the depth to which 
one of these valleys, the Yare, has been excavated and filled up 
since with silt and mud is 170 feet below Yarmouth, or about 155 
below Ordnance datum. This is not only far below the surface of 
the adjoining sea-bottom, but is below the surface of that sea-bottom 
decade n. — vol. iv.— no. xii. 35 
