122 THE FAIRY-LAND OF SCIENCE. 
parts of Switzerland where glaciers do not now exist, 
and huge blocks which could only have been carried 
by ice, and which are called " erratic blocks," some of 
them as big as cottages, have been left scattered over 
all the northern part of Europe. These blocks were 
a great puzzle to scientific men till, in 1 840, Professor 
Agassiz showed that they must have been brought by 
ice all the way from Norway and Russia. 
In those ancient days, there were even glaciers in 
England ; for in Cumberland and in Wales you may 
see their work, in scratched and rounded rocks, and 
the moraines they have left. Llanberis Pass, so 
famous for its beauty, is covered with ice-scratches, 
and blocks are scattered all over the sides of the 
valley. There is one block high up on the right-hand 
slope of the valley, as you enter from the Beddgelert 
side, which is exactly poised upon another block, so 
that it rocks to and fro. It must have been left thus 
balanced when the ice melted round it. You may 
easily see that these blocks were carried by ice, and 
not by water, because their edges are sharp, whereas, 
if they had been rolled in water, they would have 
been smoothed down. 
We cannot here go into the history of that great 
Glacial Period long ago, when large fields of ice 
covered all the north of England ; but when you 
read it for yourselves and understand the changes on 
the earth's surface which we can see being made by 
ice now, then such grand scenery as the rugged 
valleys of Wales, with large angular stone blocks 
scattered over them, will tell you a wonderful story 
of the ice of bygone times. 
