106 TRANSACTIONS OF THE [Sess. LXxv. 
2. PHYSIOGRAPHY. 
Amongst the many land-torms of the Southern Alps and 
their environs none are more characteristic than the broad 
beds of bluish-grey stones, sometimes 1°5 km. or more in 
width, over which, in many anastomosing streams, the 
rivers wander. 
In the lower part of its course such a river-bed is confined 
between high, permanent terraces clad with yellow tussock- 
grasses, but nearer the source the terraces are low and 
temporary, or altogether wanting, the river’s spread being 
limited only by the mountain slopes on either side. Thus, 
in many places, the mountain valleys consist of river-bed 
alone, the origin of which is not difficult to determine. 
The Southern Alps are built up for the most part of 
much-jointed sandstones, greywackes and slates, rocks 
which are very easily disintegrated by frost. Everywhere 
the snow-clad mountains are scarred by black patches of 
rock and present steep precipitous or craggy faces from 
which avalanches of stones, large and small, fall on to the 
glacier below in such quantities that the clear ice buried 
beneath a thick and heaped-up stony covering is frequently 
not visible for a distance of several miles from the terminal 
face. Eventually the morainic matter falling from the 
terminal face of the glacier is seized by the turbulent 
stream issuing from its ice cave and deposited on the 
valley-floor, the water exercising a powerful sorting action, 
so that the stones of the river-bed gradually decrease in 
size on proceeding towards the sea, huge blocks first of all 
dominating the scene (see Plate X.). 
Besides the actual morainic material the tributary 
torrents and lateral rivers supply vast quantities of débris, 
the mountains below the snow-line having in their gullies, 
and even on their slopes, extensive stone-fields (“shingle- 
slips”) very many metres in length, which afford an 
inexhaustible supply of material. 
The valleys themselves are plainly of glacial origin. The 
presence of numerous ancient moraines, truncated or ice- 
overridden spurs, roches moutonées and other glacial land- 
forms, testify unmistakably to a former most extensive 
glaciation, and show that the present ice is but a remnant 
