GEOLOGY 
exclusively the form of snow. Perhaps it is as well to push the com- 
parison farther, and to state that although the Glacial Period was one of 
snow and ice, yet it was not necessarily a period of very low temperature, 
any more so than characterizes the higher glacier regions of Switzerland 
to-day. 
As a consequence of the increased elevation there was land con- 
nection with the continent on both the east and the south of Britain. 
For what is now the North Sea was then a broad plain, through which 
the Rhine flowed northward, receiving as it went all the drainage of 
eastern Britain, and discharging it into the Atlantic, somewhere to the 
north-east of Shetland. The depression now occupied by the English 
Channel had already been shaped into much its present form as a river 
valley, and with the elevation referred to it remained so. The same is 
true of the Irish Sea ; and the rivers of Cumberland, joined with those of 
the south of Scotland, united with the others that now discharge into 
that area, and reached the Atlantic to the south-west of Ireland. 
(c) The occurrence of wide stretches of dry land, where now 
there is sea, had a most important effect in modifying the climate. 
Indeed, taken in conjunction with the increased elevation, and with the 
proximity of the mountain areas of southern Scandinavia and north- 
western Scotland to the vast quantities of aqueous vapour drifted north- 
eastward in connection with the Gulf Stream, the factor just mentioned 
may have played an important part in the development of the peculiar 
conditions which characterized this period. It may be as well to repeat 
in this place that the Glacial Period was not so much a period of low 
temperature, as one during which more snow fell during the year than 
the summer’s heat sufficed to melt. To bring about such conditions four 
factors are required. (1) There must be an extensive area of ocean 
where distillation by the heat of the sun goes on at a high rate. (2) The 
products must be transferred from this area by the action of currents, 
aqueous or aerial. (3) There must be an upland area in the path of these 
currents, which acts as a refrigerator, and converts the aqueous vapour 
into snow. (4) The local conditions must be such that more snow is 
precipitated than is removed from the land. These conditions are quite 
compatible with a comparatively mild climate, and do not by any 
means require so low a temperature as is generally supposed to have 
prevailed during the Glacial Period. Strictly speaking, it would be 
more correct to refer to this period as the Niveal Period, seeing that its 
essential characteristic was the widespread prevalence of snow. 
Snow does not flow off the land like water does, hence, if only 
a little more fell each year than was melted, it was bound sooner or 
later to accumulate at the valley heads until it became compacted into 
ice. In this state it must soon have begun to flow down the valleys 
in the form of glaciers. It is as well to remember that the ice simply 
took the place of river water, and moved, as rivers do, outward from 
the main areas of precipitation, downhill and seawards. 
There are good geological reasons for believing that this state of 
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