The Council Bluffs nonpareil. [volume] (Council Bluffs [Iowa]) 1857-1867, 1859-01-08
Prom Halls Geology 81 Iowa.
ORIGIN OF THE PRARIRS,

/. extensive o region, 10 one which has often
r been discussed, and in regard to which
, diametrieally opposite opinions are enter
tanned.
, The idea is very extensively entertained,
5 throughout the west, that the prairies were
, once covered with timber; but that it has
, been DESTROYED by the fires which the Indians
T have been in the habit of starting in the dry
grass; and which swep. n vast extent Of sur
face.every autumn. A few considerations will
show that the theory is entirely untenable.
In the hrst place, the praires have been
in existence at least as far back ns we have
any knowledge OF the country; since the first
explorers Of the west describe them lust m
they now are. They may be limited areas
once covered with woods, and now bare
but, in general, the prairie region occupied
tho same surface which it did when first yis-
tied by the white man.
But, again, prairies are limited to pecu-
liar region, one marked by certain charac-
terlstic Typographical and geological fea-
lures, and they are by no means distributed
about wherever the Indians have roamed and
used FIRE. Had frequent occurrence VI nres
in the woods been the means of removing
the timber and covering the soil with
dense growth Of grass, there is no reason
why prairies should not exist in the Eastern
and Middle States Us we'll as in the Western.
The whole northern portion Of the United
p, States was once inhabited by tribes differing
iaut lite from each other IN their manner Of
living.
Again, were the prairies formerly covered
by forest trees, we should probably now find
some remains of them buried beneath the
soil, or other indications of their having sx-
listed. Such is not the case, for tho occur
renee of fragments of wood beneath the
prairie surface is quite rare; and when they
ure found, it is in such a position as to show
that they had been removed to some distance
, from the place Of Their growth.
1t has been maintained by some, that the
want of sufficient moisture in the air or soil
was the cause of the absence of forests in
the Northwest: and it is indeed true that the
prairie region does continue westward, and
become merged in the arid plains which ex-
tend along the base Of the rocky mountains,
where the extreme dryncss is undoubtedly
the principal obstacle TO the growth of any
thing but a few shrubs, peculiarly adapted
! to the conditions of climate and soil which
prevail in that region. This, however, can
not be the case in the region east Of the Mis-
sissippi and near Lake Michigan, where tho
prairies occupy so large surface, since the
feSuItS VI SiON uO
lack Of moisture in that district, the annual
preci ptation being fully equal to what it is
in the well-wooded country farther east in
the same latitude. Besides the growth of
forest trees is rich and abundant all through
the prairie region, under certain conditions
of soil and position, showing that their range
is not limited by any general c.Imatologicul
cause.
Taking into consideration all the circum-
stances under which the peculiar vegetation
Of the prairie occurs, We are disposed to
consider the nature of the soil as tho prime
cause of the absence Of forests and the pre-
dominance of the grasses over this widely
extended region. And although chemical
composition NAV not be without influence in
bringing about this result which is a subject
for farther investigation, and one worthy Of
careful examination, yet we conceive that the
extreme fneness of the articles Of which the
prairie soil is compressed is pi ob ,bly the prin-
cipal reason why 1t is better adapted to the
growth Of its peculiar vegetation, than % tho
development offorests. 1t cannot fail to strike
the careful observer that where the prairies
occupy the surface, the soil and superficial
material have been SO finely colnmunited as
to be almost in the state Of m inpalpable
powder. This is due partially to the peculiar
nature Of the underlv wing rocks and the faci-
Ity with which they undergo complete de-
composition, and partly to the mechanical
causes which have acted during and sinco
the accumulation of the sedimen,ary matter
from the prairie soil.
Ifweg 20 to the thckly wooded region, like
that of the northern peninsuar of Michigan,
and examine those portions Of the surface
which have not been invaded by the forest,
We shall observe that the beds Of ancient
lakes, which have been filled up by the slow
est possible: e::iccumulation of dotrital matter,
and are now perfectly dry, remain rs natu-
| raj prairies, and are not tresspassed on by
the surrounding woods. We can conceive
of no other reason for this than the extreme
fneness of the soil which occup es these ba-
sins, and which is the natural result of the
| slow and quiet mode in which they have
been filled up. The sides Of these depres-
sions, which were once lakes, slope very
gradually upwards and being covered with
4 thick growth of vegetation, the material
brought into them must have been the cas-
en- by examination. Consequently, when
the former lake has become entirely filled up
and raised above the level of o, erhow, We
! find it covered with most luxuri, mt crop of
grass, forming the natural meadows from
which the first settlers are SUPP lied with
their first stock of fodder.
Applying these facts to the case Of the
prairies of larger dimensions farther south
we infer, on what seems TO be reasonable
grounds, that the whole region now occupied
by the prairies Of the northwest was once an
immense lake, in whose basin sediment of
almost impalpable fneness gradually accu-
mulatcd, under conditions which will be dis
! ~
basin was drained by the elevation Of the
whole region, but, at first, so slowly, that
the finer PARTICLES of tho deposits were not
they were originally deposited. After the
had been laid here. the drainage becoming
nels, the current thus produced, aided per-
quired sufficient velocity to wear down
through the finer material on the surface,
wash away portion of it altogether, and
mix the rest so effectually with the undcrly-
ing drift materials, or with abraded frag-
ments of the rocks in place, US to give rise to
a different character Of soil in the valleys
from that of the elevated land. Tho valley
soil, being much less homogeneous in its com
position and containing a larger proportion
of coarse materials than that Of the uplands,
seems to have been adapted to the growth
Of forest vegetation and in consequence Of
this, we find such localities covered with an
abundant growth Of timber.
Wherever there has been n variation from
the usual conditions of soil, on tho prairie
or in the river bottom. there is corresp pond
ing change in the character Of the vegetation.
Thus, on the prairie, We sometimes meet
with ridges of coarse material, apparently
deposits of drift, on which, from some local
cause, there never has been an accumulation
of fine sediment; in such localities We inva-
riably find growth of timber. This is tho
origin of the groves scattered over the Prair-
les, for whose insulated position and pecu-
liar circumstances of growth we are unable
to account in any other way.
The condition Of things in the river val-
leys themselves seems to add to the plausi-
bility Of this theory. In the district which
we have more particularly examined, We
have found that where rivers have worn deep