Year: 1859

rr4 From Halls Geology of Iowa.


Origin Ofthe R'rairies. 81"


49, b svsi 81 1 itt'FHs"


The subject of the origin Of the prairies or
the cause Of the absence Of trees over.so ex-
tensivc a region, is one which has often been
discussed, and in regard to which diametri-
cally opposite opinions are entertained. IS


The idea is very extensively entertained,
throughout the west, that the prsiries were
once covered with timber; but that it has
been destroyed by the fires which the Indi.
ans have been in the habit Of starting in the
dry grass; and which swept over vast ex-
tent Of surface every autumn. A few con-
siderations win show that the theory is en-
tirely untenable. . a., l.'sr ,fe,.ass.rT


In the first place, the prairies have been
in existence at least as far back as we have
any knowledge Of the country; since the first
explorers of the west described them just as
they now are. They may be limited areas
once covered with woods, and now bare; but,
in general, the prairie region occupied the
same surface which it did when first visited
by the white man. -s.,.e,...f ,..ra. ..E Z


But, again, prairies are limited to peculiar
regions, marked by certain Characteristic to-
biographical and geological features, and
they are by no means distributed about
wherever the Indians have roamed and used
fire. Had frequent occurrence Of fires 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 as well as in the Western
The whole northern portion Of the United
Estates was once inhabited by tribes differing
but little from each other in their man.
ner of living. .,.,,, ,..g ..a.. .s .


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 ex-
listed. Such is not the case, for the occur.
renee offragments ofwood beneath the prairie
surface is quite rare; and when they are
found, it is in such position as to show that
they have been removed to some distance
from the place of their growth. s a


1t has been maintained by some, that the
want of sufficient moisture i /, Il e air or sol
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 dryness is undoubtedly
the principel obstacle to the growth of any
thing but 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 tn.
Mississippi and near Lake Michigan, wher,
the prairies occupy so large a surface, sinc'
the results Of meteorological observation.
show no lack of moisture in that district
the annual precipitation being fully equal t.
what it is in the wel-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 Genealogical cause


Taking into consideration all the crcum
stances under which the peculiar vegetation
of the prairie occurs, we are disposed to con
slider the nature of the soil as the prime cause
ofthe absence offorests and the predomenancs
of the grasses over this widely extended re
gion. And although chemical composition
may not be without influence in bringing
about this result which is subject for far
ther investigation, and worthy of careful ex
animation, yet We conceive that the extreme
fineness of the particles of which the prairi,
soil is composed is probably the principa
reason why it is better adapted to the growth
of its peculiar vegetation, than to the devel
,opment of forests. 1t cannot fail to strike
the careful observer that where the prairies
occupy the surface, the soil and superficial
material have been so finely communited as
to be almost in the state of an impalpable
powder. Thisis due partially to the peculiar
nature of the underlying rocks and the ia
cility with which they undergo complete de.
composition, and partly to the mechanical
causes which have acted during and since
the accumulation Of the sedimentary matter
from the prairie soil.


If we go to the thickly wooded region, like
that of the northern peninsular 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 accumulation of dotrital matter,
and are now perfectly dry, remain asnatural
prairies, and are not tresspassed on by the
surrounding woods. We can conceive of nc
other reason for this than the extreme fineness
of the soil which occupies these basini, and
which is the natural result of the slow and
quiet mode in which they have been filled
up. The sides of these depressions, which
were once lakes, slope very gradually upwards;
and being covered with thick growth of
vegetation the material brought into them
must have been the same by examination