178 Reviews—Dr. Penck—Glaciation of the German Alps. 
east of the Rhine is this northern calcareous chain broken through ; 
by the valleys of the Inn, Salzach, and the Enns. The valley of the 
Inn forms a deep trough about 150 kilométres in length, between 
the central chain, from which it receives numerous affluents, and the 
North Alps; and it finally bursts through the northern calcareous 
chain at Kufstein. None of the valleys between the Rhine and the 
Inn which run northwards from the Alps, extend through the 
northern chain of calcareous rocks, and thus never reach the districts 
of the crystalline schists; but at the heads of most of these valleys 
there are deep gaps or notches opening into the Inn Valley, about 
1000 metres below the average height of the crests of the range, 
and from 500 to 800m. above the bottom of the Inn Valley. 
Through these notches run most of the passes which lead from the 
valleys of Upper Bavaria into the Inn Valley. The mighty glaciers 
of the glacial period which descended the Inn Valley overflowed 
through these notches, and thus found their way along the valleys 
running northwards into the Bavarian high-level plateau. 
The Boulder-clay of the Upper Bavarian plateau partly corresponds 
in character with the ground moraines of the present day, and with 
the Boulder-clay of northern countries. It consists of layers of mud 
and stones, from 60 to 70m. in thickness, which the author states 
must have been carried forward under and through the motion of 
the ice, and not by being frozen into its substance. This clay 
contains, mingled together, portions of every kind of rock traversed 
by the glacier, and thus indicates the path which the glacier must 
have followed. On the Bavarian plateau it is filled with erratics 
from the crystalline schists of the central Alpine chain, together 
with fragments of Triassic, Jurassic, and Cretaceous strata from the 
northern chain, and portions of Tertiary Flysch and Molasse from 
the districts at the foot of the northern chain. On the sides of the 
Inn Valley erratics have been transported to heights of 1830 m. §. L. 
or 1170 m. above the present level of the valley, and at Kufstein, 
where the Inn cuts through the northern chain, the erratics reach 
to 1400 m. 8. L. or 850m. above the level of the valley. It is 
therefore probable that the old glacier at Innsbruck attained a thick- 
ness of 900 to 1000 m., and therefore sufficiently high to overflow 
many of the passes leading from the Inn, northwards, into the 
valleys of Bavaria. 
One of the most important gaps on the north side of the Inn 
Valley is that of the Fern pass. It is between 2 and 3 km. in width, 
bounded by high walls of rock on both sides, and its highest point 
is 1250m.S. L. and 600m. below the line of erratics. This gap 
leads into the Loisach Valley, and thus leaves open a clear course 
for the old glaciers to have poured a stream of ice northwards. But, 
curiously enough, though the characteristic erratics of the Inn have 
been carried over neighbouring passes, 350 m. higher than the Fern 
pass, none are to be found in this pass, and the probable explanation 
is that the Fern pass did not exist at the time of the great glaciation, 
but that it has been formed since then by the solution of beds of 
gypsum and the caving in of the overlying Dolomites. Lower down 
