134 
NATURE NOTES 
enormous “ fields ” of ice occur over the sea around the Arctic 
coasts. 
If we next go to Switzerland, we find the tops of the moun- 
tains to be covered with ice. This has been formed in the same 
way as in Greenland, viz., from snow consolidated into ice by 
pressure. As it falls on inclined surfaces, its own weight causes 
it to slide down the rocks, lubricated by the water below formed 
by the melting on the surface. This, however, is not enough, 
for the glaciers in time come down to almost horizontal plains, 
as in the Valley of the Rhone, and they still move on as before. 
The causes of this glacier-motion have much perplexed physicists, 
for it is found that they move faster by day than at night, faster 
in summer than in winter, and faster at the top than at the 
bottom. But what causes these movements? Many theories 
have been propounded ; but they have been offered on observing 
ice on a small scale. The interpretation is simple enough when the 
phenomena of ice are studied over large areas. It is simply due 
to changes of temperature, of course assisted by gravity as long 
as there is any inclination at all. Thus, on the great lakes of 
North America, the ice behaves precisely like most things, viz., 
it expands under a rise of temperature and contracts under a 
fall : the sheet of ice on the lakes actually rises several inches 
above its original level on warm days ; and contracts so as to 
form cracks when the temperature is lowered. This alternate 
expansion and contraction of the whole glacier, modified in detail 
as stated above, cause it to move along the line of least 
resistance, i.e., downwards and onwards. 
Frost causes large and small masses of rock to split off the 
sides of the ravines ; they then fall on to the surface of the 
glacier and form two long mounds of rock — pebbles and dirt, 
constituting the so-called “ moraines.” These are carried down 
and finally, it may be after many years of progression, are 
deposited at the bottom in front of the glacier, forming enormous 
heaps of rubble. Sharp stones falling between the glacier and 
the rocky sides get “ set ” in the ice, and as they move along they 
scratch and score the surface of the rocks. At the same time 
the rocks below get ground down and smoothed over. 
We have no longer any such glacier-action in Great Britain ; 
but we had formerly. Snowdon and the Scotch mountains, like 
Mount Blanc to-day, furnished an abundant supply. Grooves and 
scratches may be seen on all sides far down into the valleys below ; 
while the lower slopes are composed of the “ terminal moraines,” 
upon which seaside towns, such as Penmaenmawr, are sometimes 
built. Large blocks of stone, scored and scratched, appear as 
“ boulders ” in the meadows near to that towm ; and it will be 
noticed by their nature that they have all come from a distance. 
Besides terrestrial glacier-action, we are not wanting in the 
evidence of coast-ice. In East Anglia the soil consists of 
“ glacial clays,” some loo feet or more in thickness in places ; 
and, if the heaps of stones collected off the fields for mending 
