180 Reviews—Dr. Penck—Glaciation of the German Alps. 
sands, which dip at an angle of 10° to 20° away from the direction 
of the glacier. In places these stratified materials are heaped and 
crumpled together. Penck states that these terminal moraines could 
only have been produced by relatively stationary glaciers, as a con- 
tinually advancing glacier would override the terminal wall, and a 
retreating glacier would not form one. The stratified moraines he 
considers as due to the action ofthe water streaming from the end 
of the glacier on the ground and terminal moraines. By the con- 
stant action of the glaciers in pushing outwards morainic materials, 
the margins of the districts over which they extended would gradu- 
ally become higher than their central portions, and thus these 
terminal moraines inclose central depressions, which, when the outer 
wall is not broken through, frequently appear as lake basins. This 
central area shows distinctive features of the eroding action of the 
glacier, whilst the outer marginal area affords convincing proofs of 
its power of heaping up the materials which have been transported 
in a forward direction under its bed. The district of the old Isar 
glacier furnishes a well-marked instance of this fact, for whilst its 
northernmost border moraines are more than 600 m. above the sea, 
the levels of the Ammer See and of the Wurm See, inclosed by 
these moraines, are only 440m. and 460m. 8. L. respectively. 
Another important feature of the glacial deposits in the Upper 
Bavarian plateau is the presence of widely extended beds of rolled 
gravel which underlie the morainic materials. These are exhibited 
more particularly at Murnau, on the borders of the Staffel See, in 
the Loisach Valley, and in the wide plain of which Munich is the 
centre. These gravels are named “ Lower Glacial” (untere glacial 
Schotter). The materials of these gravels must originally have been 
transported by glaciers, for they contain fragments of crystalline 
rocks, and none of the valleys in which they occur reach into the 
crystalline range of the Alps. The dam which separates the Achen 
See from the Inn Valley is formed of this Lower Glacial gravel, 
mingled with sand and clay beds. 
In many places, too, similar beds of rolled gravel with sand and 
clay overlie the ground moraine, and appear to have been formed by 
the water from the melting ice during the recession of the glacier. 
In a chapter treating of the Alpine inland ice the author shows 
that in the Glacial Period the Alps were, as also at present, great 
centres from which glaciers streamed on all sides. At present in the 
Eastern Alps the permanent snow-line is 2800m. 8. L., and the 
lower boundary of glacier extension 1750 m. 8. L.; but the old 
glaciers descended as low as 550 m. §. L., and it is therefore probable 
that the permanent snow-line at the time of the greatest extension 
of the glaciers in this district may have sunk to 1600 m. 8. L. The 
enormous accumulations of ice reached nearly to the tops of the 
mountains, and thus there could not have been any great amount of 
morainic material on the surface of the glacier. The old moraines 
were undoubtedly produced by the erosive action of the glacier in the 
higher regions. The force of glacial erosion is shown by observa- 
tion on the amount of fine sediment in streams issuing from glaciers 
