The San Francisco call., 1903-12-01

HAMIInE
Mar and the Glacial Period, etc)
ocopyrfght 1903. by Joseph B. BoN-les-)
Those who live in the well-watered
portions Of the world, where rich vege-
tation covers the surface and protects
il from the denuding force Of the wind,
can have little realizing sense Of the
effectiveness Of this ever-active geo.
gicaI agency. Yet even in some we'll
watered regions dunes are familiar
phenomena. Dunes are simply drifts
Of sand, closely resembling the snow
drifts Of winter, and protection against
them is secured by similar means. AS
in snowy regions one sees long lines Of
close board fences some distance from
the windward side OF the railroad to
stop the drifting snow on its
onward career. so he may in
many places see windbreaks 10
stop the drifting sand. But in many
cases where a windbreak is not suf=
hcient a constant force Of workmen is
necessary 10 remove the sand from the
track at stated intervals or after every
unusually severe storm. At such places
the railroad companies. TO their sor-
row, learn the enormous power Of this
constantly acting geological force in
transferring finely comminuted earthly
material. from one place 10 another.
one Of the best known localities for
observing dunes is found on the south
eastern shore Of Lake Michigan. Near
y all. II not all, the railroads ap-
preaching Chicago from the east pass
through this series Of dunes as they
come around the southern end Of the
lake. Many of the dunes are very
fresh. with no covering Of vegetation,
and rise. like snowdrifts. fifty feet or
more above the general level. Others
are Of such age that they have been
covered more or less with vegetation,
trees OF considerable size being found
upon them. But in all cases the ac-
tion Of the wind. in moving the sand
southwark from the lake, is evident
The wind blowing from the north keeps
an exposure Of bare sand upon that
side and drifts it over into exposures
of equally bare sand upon the outer
margin. The width Of this belt Of
dunes around the south end Of Lake
Michigan averages a little more than
one mile. The material, being clean
washed sand is unfit. for agricultural
purposes, and the area is occupied by
very few houses. and those mostly be-
longing TO railway employees.
-
I'll - 7foi,
these dunes are composed and the rate
Of its movement are subjects Of great
interest. The sand is derived, in the
first place. from the shores Of the lake
farther UoIth, which are constantly be-
ing eaten into by the waves and cur
r nts. All along the western shore,
from Evanston TO Racine, the waves
are wearing away the shore at an av-
erage rate Of three or four feet per an
nam. The material that falls into the
lakes from the bluffs thus erOded is
"a orlzed over by the waves until the
very finest particles are washed out
ard hoated into deep water, while the
81 nd remains near the shore and is
gradually washed southwark by the
prevailing currents. Every one ir
Chicago knows how land is forming or
the shore, giving rise to legal contests
as 70 ownership. From observations oi
the United States engineers it was
found that I2s 900 cubic yards Of sand
were annually stopped by the two piers
which were extended out into the lake
70 deep water. This vast amount rep
resented. however, but a fraction Of the
whole amount Of sand that was being
carried by the currents past Chicago
10 the south end Of the lake.
On reaching the south end Of the Lake
the sand is washed up by the wave.
during storms and left for a consid
cradle portion of the year exposed L
the action Of the winds, which have
drifted IL out into the belt of dunes
with which so large a portion of the
travelling public is familiar. But owins
10 the fact that the prevailing winds O.
this region are westerly the larges
sccuraulation OF dunes Is found upoI
the esst shore. in Michigan. Traveller
upon the Michigan Central Railroad
cannot fail 10 have noticed these gres
drifts Of sand, nearly 100 feet high. a
Michigan City. This belt Of dunes
cDgAA q AArAA ANA u a AAlAAA lAclllf
sometimes TO more than 100 feet Il
height, extends northward all along tn
shore. being specially prominent at ST
Joseph and Grand Haven. In man!
places they threaten TO overwheln
whole villages and TO compel the rail
roads 10 remove their tracks 10 get ou
of the way Of the drifting material
while IN some cases houses and forest
have been buried out of sight.
It has been profitable. 10 dwell thu
fully upon the dunes around the south
eastern portion of Lake Michigan, no
because they are the largest or tn
most conspicuous in the world, but be
cause they are the most accessible an,
the best known to the people Of tn
United States. In some respects a stil
more interesting belt Of dunes occur
IN Western Nebraska, stretching nearl!
across the northern part of the State
approximately parallel with the cours
of the North Platte River, but at
distance OF many miles from it. Thi
consists of a belt Of sand hills a half