THE FORMER EXTENSION OF GLACIERS. 1 55 
Morlot was primarily led to this conclusion by 
his observations in the valley of the Dranse, south of 
Thonon on the Lake of Geneva, which I had the 
pleasure of visiting under his guidance. In this gorge 
between two well-marked glacial deposits is a deposit 
indicating a milder climate. 
Again, at several places in the Canton of Zurich 
are beds of lignite, sufficiently thick to have been 
worked for fuel. They are intercalated between 
glacial deposits; they indicate a luxuriant vegetation 
and consequently a mild climate; they contain, more- 
over, remains of animals, such as the Hippopotamus, 
which could not support great cold. This can only 
be accounted for, I think, by assuming that these 
groups of animals occupied the country alternately. 
Moraines which have been long exposed to the 
atmosphere become gradually modified at the sur- 
face. The pebbles are much weathered and some- 
times quite disintegrated, even those of Granite crum- 
bling into a sort of clay while retaining their original 
form. The layer affected may have a thickness of 
one to two feet or even more. This weathered crust 
often assumes a reddish colour, whence it is called by 
Italian geologists “Ferretto.” 
Where an old moraine has after a long interval 
been covered by a later one, the Ferretto enables us 
