which
takes the
form of the
glacier border,
i.e.,
it
closes off the
valley in
a
horse-shoe
fashion,
with the
open
side
directed
upwards.
Such
rows
of
hills
are
called moraine hills.
They
consist of
angular
rocks of all sizes. However, if the glacier retreats slowly, it will
distribute
these blocks of rock in the
area
of retreat quite
uniformly.
This
retreat
region
will also be landform
tongue-shaped
like the
glacier
itself. If the moraine
strips
in the lower
part
of
the
glacier
do not mix but form
separate
bands, the
deposited
rocks
will form interrupted
lines
(rows).
Thus the moraine hills
indicate
a
maximum
or a
halt in the expansion of
a
glacier, and erratic boulders
a
retrogression,
but most of all
they
are
proof of
an
earlier
presence.
Thus,
these
blocks
consist of
alpine
rocks
and hence in
general
differ
from
the kind of rock
prevalent
at their
site,
are
angular
and sharp-edged, form systems.
[Fig.] Schematic
representation
glacier
erratic blocks moraine
region
of retreat
The
glacier
also
acts
upon
the
rocks at
its bottom. Softer rocks
get
finely ground,
harder
ones
get
striated
by
friction and rounded
moraine
direction
of
valley
moraine
[Fig.]
by
water.
They
are
then carried
away
by the
glacial
water
and
deposited
when the
pushing
force of the water becomes too weak to
carry
them further. Such
deposited
rounded, striated rocks
are
often
found where there
now
flows
an
eroding
stream, which does not deposit
rocks because the deposition takes
place in
a
lake that is farther
up.
If this lake is determined
by
the structure of the
mountains,
then it
is
certain
that the
glacier
has reached
beyond
the lake
during
such
deposition periods.
If
more
than
one
period
of such
depositions
can
be discerned
(gravel terraces),
as
for
example
in Aarau, then this is
proof that the
glacier
went
beyond
the lake
on
more
than
one
occasion,
giving
rise to deposition, and retreated
as
many
times, which implies
an era
of
erosion for the lands
lying
further below the lake.
All
these
criteria
are
found in
Switzerland.
The
region
of
erratic boulders extends
as
far
as
Germany. The
sites
of such
boulders of the
same
kind of rocks form wide
strips
which
narrow
toward the
mountains and lead to
a
mountain
region
in which these
rocks
crop
out. The characteristic
streaking
(alpine
line)
can
be
found
on
valley walls
where
there
are no more
traces of
glaciers.
It is
possible
to distinguish
between various
moraine systems, which
indicate
periodic
halts, which
[the halts]
are
analogous in different
glacier regions. Gravel terrace formation
is
found
frequently
and
points
to different
glacializations.
26.
MATURA
EXAMINATION
(F)
ALGEBRA
[21 September
1896, 9:30-11:30
A.M.]
Albert Einstein
Given
are
the distances l,
m, n
between the center of
an
inscribed circle and the
corners
of the triangle. Find the radius
p
21
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