The San Francisco call., 1904-02-09
INSTRUCTIVE JTUDHg
BY lNOTEDAGSN AND
uISSFfEN


and thus the species which they rep
resented would slowly spread south
ward until the glacial period had ex-
hausted itself and the extreme limit OF
favora bic conditions had been reached.
Thus it would result that the same
species would be driven down 10 cor
responding latitudes on both sides of
the Pacific and Atlantic oceans and we
should have what now appears
namely, the same species of plants in
Japan. the middle United States and
Europe and Northern Asia.
But it still would seem to be puz-
zle why the plants were not the same
IN corresponding ATTITUDES on both
sides of the American continent. Why
should the species of plants in Cali
fOrnia be so different from those in
Pennsylvania and Virginia? This is
answered by considering the different
conditions which prevail on the east
and west sides of a continent Be
cause the world turns from west to
east the prevailing winds in the north
ern hemisphere are from the south
west The breeZes of the Pacific coast
are therefore sea breezes, laden with
moisture, while those in the Eastern
Atlantic States are land breezes,
which have been largely bereft of their
moisture and are subject to greater
alterations of temperature. The con-
stant action Of these diverse conditions
would have a direct effect 10 favor
some species on the Atlantic coast that
would not be favored on the Pacific,
and vice versa. Thus we have every
thing accounted for in a most natural
way.
The reason why these plants have
not returned to Greenland and Spitz-
bergen is that the glacial period is
not vet over It still prevails in those
northern regions. But they have start
ed on their northward journey and have
partially recovered the ground lost.
Some have already attained their orig
iual homes. leaving, however. many
straggIers On the way. The main body
Of Arctic vegetation is the same with
that which covered the country on the
Middle Atlantic States during the eli
max of the glacial period. OF the strag-
Cling remnants still left in favoring
situations one Of the most interesting
is Scotch heather, which is found not
only in Labrador, but in a few places
in Massachusetts, like Andover and
Cape Cod. In all the rocks gorges open
ing into Lake Erie remnants of the
glacial vegetation are preserved in the
sequestered and cool shady hooks.
Some such are also preserved in SINH
lar narrow, cool gorges opening into
the Ohio River below Cincinnati.
But the mountains formed the best
retreats for the Arctic plants. which
were following up the receding ice
sheet Alpine plants are found on the
high elevations of the White Noun
tains and on the high peaks of the
Rock and Sierra Nevada Mountains as
far south as New Mexico, but are alb
sent over all the intervening areas.
These colonies of Arctic species on the
tops of the mountains of the northern
hemisphere are related 10 the atmos-
phere. as the plants on islands are to
the water of the ocean, and are most
important witnesses to the reality and
extent of the continental ice fields
which characterized the glacial period.
A mountain top is an island in the air.
One can reach Arctic conditions by go
ing up as web as by going north.
In some respects the effect of the
glacial period upon animal life and dis
tribution was even more peculiar than
that on plants. During that period
large number of Arctic species were
crowded down into Central Europe and
into the Middle and Northern States of
the Atlantic coast and Mississippi Val
ley. II company with mans remains
there are found those Of the grizzly
bear, the Irish elk, the reindeer, the
musk OK and the Arctic fox, while the
lbeX and the chamois, which now oc-
cupy the high mountain crags, descend
ed to the valleys. Several of these
northern species now extinct were also
present in those temperate regions.
The indirect effect Of this incursion
Of Arctic animals into the temperate
zone was to cause the destruction of
many animal forms which already oc-
cupied the region. Just before the gla-
cial period there were living in America
two extinct species of the cat family
as large as lions, four species of the dog
family as large as wolves, while the
walrus was found in Virginia, the sea
COW in South Carolina. There were also
living six species Of horses, the South
American tapir and llama, a camel, two
species OF buffalo, three species OF
sheep, two species of elephant and two
OF mastodons, a species of megathe-
rum. three Of megalonyx and one of
mylodon-huge terrestrial sloths as
large as the rhinoceros or even as the
elephant. All these and several more
species we're either destroyed by the
competition of the northern animals or
were driven back into South America.
The destruction of so many widely
spread species of animals occupying
North America just before the glacial
period is one of the most startling rev.
elations Of geology
Insects also. as well as plants and the
larger animals, were compelled to
reckon with the glacial period. Among
the most interesting illustrations of
this occurs in the White Mountains,
where various Alpine species Of butter
flies are found near the summit In
ascending Mount Washington one sud-
denly encounters near the top whole