1 56 SCENERY OF SWITZERLAND. 
to distinguish between the two. It is in fact a strong 
confirmation of the existence of inter-glacial periods, 
during which the glaciers retreated, and a more 
genial climate prevailed. At Ivrea, for instance, the 
presence of Ferretto shows that the gigantic moraine 
known as the Serra was not formed during one long 
continuous glaciation. r lhe moraines which are coated 
with Ferretto occupy as a rule the outer side of the 
morainic amphitheatre, and are covered on their 
inner edges by the later and inner moraines. Lignite 
beds also occur on the south of the Alps* One of 
the places where an inter-glacial period is most clearly 
shown is in the valley of the Inn. At Hottingen, 
close to Innsbruck, is a great fluvio-glacial deposit, 
reposing on a ground moraine at a height of 1300 
meties above the bottom of the valley, and capped 
to a height of 1900 metres by another. In these 
fluvio-glacial beds forty-one species of plants have 
been found and studied by M. Wettstein. Of these 
twenty-nine now live in the immediate neighbourhood, 
six in the Tyrol, but at a lower level, six further 
south, and four have not been determined. Here 
then we have evidence that the valley of the Inn 
was (firstly) filled by a glacier to the height of 1300 
* Riitimcyer, Ober Pliocene tend Eisperiode auf beiden 
Seiten der Alpen. 
