Paleo-Geological and Geographical Maps of the British Islands. 289 
valley of the Forth, by Professor Geikie* and his brother. The sheets of ice 
descending from the Grampians were met by those descending from the snowfields 
of the southern uplands, and both united took an eastward course till being opposed 
by the heavy masses of Scandinavian ice blocking the north sea, the stream 
was deflected southwards and passed along the north-east coast of England. The 
extreme southerly margin of the ice was limited by its melting, and doubtless 
numerous muddy streams issued forth at its base, while the Atlantic was filled 
by large bergs breaking off at the ice-foot and floating southwards with the 
oceanic current, as in the Greenland sea at the present day. 
Mr. W. Keeping has recently given valuable information regarding the Glacial 
deposits of Central Wales.t+ 
In the south-east of England, the Lower Boulder Clay of Lancashire was pre- 
ceded by beds of gravel and clay with erratics, constituting Mr. J. S. Wood’s 
“Middle” and ‘“‘ Lower Glacial” series, and by which the great Chalky Boulder 
Clay, the true representative of the Lower Boulder Clay of Lancashire, is separated 
from the Norwich Crag.{ 
Elevation of Land.— There is reason to believe that during this early stage of 
the Glacial period the land was elevated, and that much of the shallower portions 
of the sea-bed were laid dry. Under these circumstances the South of England 
would have been united to France (as shown in Plate XXXIV.), while the north 
sea would have been shallow. But, as Dr. Croll believes, the mass of ice from 
Scandinavia was so great that it took possession of the north sea, dislodging 
the waters which were insufficient in depth to break it up, and float it away in 
the form of bergs. 
As regards our knowledge of the direction of the ice-flow, the evidence is mainly 
of two kinds, that derived from the lines and eroovings found on rock-surfaces 
wm situ; and that derived from the nature of the Boulder Clay, or Till, and the 
stones or boulders it contains. It being assumed that this deposit has been formed 
by the ice-sheet, the stones which it contains can often be traced to their sources, 
and thus the direction of the ice movement becomes known.§ 
On the other hand, erratic blocks strewn over the surface are not to be relied 
upon as evidence of the former presence of an ice-sheet, as in many eases they have 
been carried by floating ice from their original sources at a time when the country 
was partially submerged. The periods of submergence follow that of the great 
ice-sheet, and are illustrated in the succeeding maps, in Plate XXXV. 
* Geological Map of Scotland, “The Great Ice Age,” &c. 
T Geol. Mag., No. 216 (June, 1882). : 
} I agree with Dr. J. Geikie in considering Mr. Wood’s Cromer Series as preceding the Lower Boulder 
Olay of the West of England, and as representing probably the true Till, with fresh-water beds lying at 
the base of the Glacial Series of Scotland. 
§ Mr. D. Mackintosh has ably carried out observations of this kind. 
TRAXS. ROY. DUB. 80C., N.S., VOL, I. SB 
