20 
GLACIAL PERIOD. 
fess that this distant retrospect of the subject 
has been to me almost as fascinating as were 
the reearclies of my earlier years in the same 
direction. I wish that I could present it to 
the minds of my readers with something of the 
attraction it possesses for me. I trust, how¬ 
ever, that I have made it plain to them that 
the great mountain-chain of the Alps has been 
a central axis from which immense glaciers at 
one time descended in every direction, not only 
to its base, beyond which the lowlands extend 
in flat undulations, hut to a greater or less dis¬ 
tance over the adjoining plains ; while at pres¬ 
ent they are confined to the higher valleys. 
The first attempts at a generalization concern¬ 
ing their origin started from the assumption 
that they must have been formed between the 
high ridges from which they seem to flow down. 
My own theory was also at first, that the up¬ 
heaval of the Alps must, in some way or other, 
have been connected with these phenomena. 
But it soon became evident to me that these 
views were inadequate to account for the for¬ 
mer presence of extensive glaciers in other 
parts of Europe ; and even within the range of 
the Alps there were insuperable objections to 
