St. Charles City Republican intelligencer. [volume] (St. Charles City [Charles City], Iowa) 1857-1861, 1859-08-04
Stiienti6t.
GEOLOGY OF IOWA.
EXTRACTS PROM HALLS GEOLOGICAL SURVEY.
THE PRAIRIES

THE PRAIRIEs.
Upon the great prairies Of Central
Iowa, one may frequently travel over
a large extent of surface, without see
ing single stone, not even so much
as the smallest pebble. In the swales
and in some of the bottom lands, cs-
pc ecially in the southern part of the
State, the rich black vegetable mould
is very deep, but on the prairics it is
usually from one to two feet. The
subsoil is almost invariably quite az
gillaccous loam and there is a gradual
passage downwards into a material
in which, though containing sandy
portions and occasional pebbles, the
argillaccous element greatly prcdom
mates.
The thickness of the superficial de-
reaching the solid rock is, Of course,
very variable in different parts of the
State. There are sometimes accumu-
lations of clay, sand and loan to a
depth of nearly 200 feet while in
other places the rocks are barely con-
cealed The deepest accumulatlons,
however, we conceive to be mainly
confined to the vicinity Of the great
rivers, as we have no evidence that,
in the interior of the State and away
from the water-courscs, the superficial
deposits have anything like the depth
mentioned above. Indeed the wells
which are sunk on the prairie are
usually quite shallow, and almost new
or. so far as we have observed, reach
the rock, so that we have not the
means of fascertaining accurately v what
the depth of the whole body of super,
fetal material is. In general water
is struck atfrom l5 to 30 feet in depth,
as soon as q more gravclly stratum is
intersccted
ORIGIN OF THE PRAIRIEs.
The subject of the origin of the
prairies, or the cause Of the absence
| of trees over so extensive region, is
one which has often been discussed,
and in regard to which Numerically
opposite opinions are maintained.
The idea is very extensively enter
taincd, throughout the West, that the
prairies were once covered with tim
! bcg but that this has been destroyed
by the f.es which the Indians have
been in the habit of starting in the
dry grass, and which sweep over a
vast extent of surface every autumn
A few considerations will show tha
this theory is entirely untenable.
In the first place, the prairies have
been in existence at least as far bacl
as We have any knowledge of the
country since the first explorers Of
the West described them just as they
now are. There may be limited areas
once covered with woods, and now
bare but in general, the prairie re
gion occupies the same surface whicl
it did when first visited by the whit
man.
But, again, the prairies are limite
to peculiar region, once marked b.
certain characteristic Typographical
aud geological features, and they ar
by no means distributed about whel
ever the Indians have roamed an,
used fire. Had the frequent occur
renee of fires in the woods been thu
means Of removing the timber anc
covering the soil with dense growtl
of grass, there is no reason why pral
/ res should not exist i'll the Eastern
/ and Middle States as well as i'll th'
. Western. The whole northern portion
, of the United States was once inhat
f tied by tribes differing but little from
each other in their manner Of living.
Again, were the prairies formerl,
covered by forest trees, we shoul'
probably now find some remains o
them buried beneath the SOIL or othe
indications of their having formerl,
existed. Such is not the case, for til,
occurrence of fragments of wood be
meath the prairie surface is quite rare
and when they are found, it is in sucI
"a position as to show that they hav,
been removed to some distance from
, their place of growth.
1t has been maintained by some
that the want Of sufficient moisture i
, the air or soil was the cause of tn
/ absence of forests in the Northwest
/ and il is indeed true that the prairi
: region does continue westward, an
4 become merged in the arid plain
: which extend along the base of tn
5 Rocky Mountains, where the extrem
, dryness is undoubtedly the principa