Clearfield Republican. [volume] (Clearfield, Pa.) 1851-1937, 1877-06-27
the ORIGIN OF PRAIRIES.
WHY THEY ARE NOT FNcRoAcHED UPON
by BORDERING WOODS.

In q paper in the American Natural
ist, Prof J, d. Whitney, alter showing
the insufllciency OF the ordinary theo.
ries TO explain why prairies are not
encroached upon by bordering woods,
offers the following explanation of his
own:
"Let us turn at present to the geo
logical side OF the investigation. The
whole OF New England and New York,
and a large part OF Ohio and Indiana,
together with the whole Of Michigan
and of Northern Wisconsin, constitute
region over which the northern drift
phenomena have been displayed on a
grand scale. Consequently almost the
whole of this area is covered with
heavy deposits of course gravel and
boulder materials. These deposits, if
not nf tho surface, are near il, and the
finer materials deposited on them, by
alluvial and other agencies, generally
form only thin covering for the course
deposits beneath. But as we 60 south
and west from the region indicated
above we find the underlying rock
the "bed-rockp as the California miners
would call it-deeply covered with
loose materials, IL is true, but we OBJ
serve also that these are quite differ
ent in character from what they are
to the north and east. We come TO a
region where the drift agencies have
been very limited in their action. The
bulk Of the superficial detritus has been
formed from the decomposition OF the
underlying rock, and this detritus has
been little disturbed or moved from
its original position. If erratic de.
posits exist, they are usually deeply
covered with finer materials derived
from close at hand. A great area ex-
lists in Wisconsin and Minnesota over
which not single drift pebble has
ever been found, either at the surface
or at any depth beneath IT, The strata
have become chemically disaggregated
and dissolved by the percoation of the
rain through them, the calcareous mat.
ter has been carried off in solution,
and there Is left behind as a residuum
the insouble matter which tho rock
originally contained, aud which, con
sisting largely Of silica and silicste of
alumina forms by its aggregation a
silicious and clayey deposit OF almost
implicablc fneness 1t is this fine ma.
terial which makes up the bulk Of the
prairie soil and as the writer con
ceives, it is this fineness which is es-
pecially inimical to the growth Of trees
Exactly as we see the desceated lakes
in the midst of forests gradually filling
up with finely comminuted materials
and becoming covered with a growth
Of grasses or sedges, which is not af.
forwards encroached on by trees, no
matter whether tho ground becomes
completely dry or whether il remains
more or less swampy, so we have the
prairies, which have certainly never
at any time been oversprcad with for
ests, and which would always remain
as they are, providing the climate un-
derwent no radical change and they
were not interfcrcd with by man. 1t
is for the vegetable Psychologist TO say
why this fneness OF the soil is so un-
favorable to the growth of trees il is
for the geologist and physical gcogra-
pher TO set forth the facts which they
may observe within the hnc of their
own professional works"