St. Charles City Republican intelligencer. [volume] (St. Charles City [Charles City], Iowa) 1857-1861, 1859-09-01

tpn OF these two formations is secured
by the dcnndation af the highest one,
and it's finely comminutcd materials
are widely spread over the lower stra-
Ia, forming with other materials the
broad cXpansc Of prairie deposit of
the West.
The lower geological formations,
/ therefore, of this great northwestern
plateau are the same as those known
III Ncw-lork and Pennsylvania, which
form not only the undiSturhcd portions
OF that part Of the country. but also
the disturbed regions of mountain
ranges, whether known as the Green
mountains, the White mountains, the
Allegheny mountains, or the Appala-
chian chain
In tracing westward the geological
formations as known in New York
and Pennsylvania, we find them, with
one or two exceptions, gradually be-
coming thinner, until at last several
Of them are scarccIy y recognizable, or
are 50 attCnuatcd as to be overlooked
IN country deeply covered by mod
crn deposits.
The Potsdam sandstone, which can
hc traced from Northern New York
and Canada 10y the st. Lawrence, and
thence bordering the north shore Of
Lake lluroa and the south shore of
Lake Superior, spreads out in Wiscon-
sin, Minnesota and Northern Iowa,
preserving mostly uniform thickness,
and showing an elevation above the
Mississippi of more than five hundred
feet, which is equal to its usual thick
ness IN more eastern localities. The
succeeding Calclerous sandstone is
likewise traceablc, with some inter
ruptions, over the same area, and is a
usual accompaniment of the Potsdam
sandstone. Not unfrequcntly the two
are so closely incorporated at their
junction, as to show that they are
parts of one formation, which has be-
come more and more calcarcous, until
it is seen as Il limestone or dolomitc.
The succeeding imestones of the
Chazy, Birdscye, Blackriver and Trcn-
ton, can he traced from New York
and Canada, along the northern side
of Lake Ontario and Lake Huron, and
thence to the north of Lake Michigan
and the western borders of Green Bay,
where they trend westerly to the Mis-.
sissippi river. But they have greatly
thlnncd towards the west and in
stead of the marked features present
ed by the same rocks in PENNSYLVANIA,
New York and Canada East, they form
low and often inconspicuous cscarp-
mcnts above the upper or St. Peters
sandstone, which represents the Chazy
limestone in part, and has thickness
of from sixty to eighty feet.
This diminution of the lower lime
stones is i'll measure compensated
by the accession of the Calena or
hcad-bcaring limestone, which is an
upper member of the Trenton lime
stone series not developed in the East,
but forming in Wisconsin. Illinois and
Iowa, more conspicuous feature than
the Trenton limestone proper.
In the Hudson river group and sue
cccding Oneida conglomcrate, most
marked change takes place the for
mcr is estimated to have, in PcnnSyl.
vania, n thickness of six thousand
feet, and the latter a thickness of one
thousand eight hundred feet while
the sam" rocks along the Green noun
tain range and in Canada, are in even
greater force. This group of strata.
consisting of green, blue and red
shaIcs, Shaly sandstoncs and some
beds of limestone, can be traced west
ward from Canada and New York, 10y
Lake Ontaria and Lake Huron, by
Point aux Bales at the northern cx-
trcmity of Lake Michigan, and thence
from below the head of Green Bay
and by the eastern side of Lake Win
nehago, and at intervals across the
State of Wisconsin. Along this line
of almost continuous outcrop there is
a constant thinning Of the beds, until
at last the whole group has diminished
to a thickness Of less than one hun
drcd feet. Thus we see that the group
Of strata, forming the most conspicu-
GUS feature III the Green mount aims,
with thickness greater than the ac-
tual height of these mountains, and
making up large part of the whole
Appalachian chain, has become so in
significant that it had never been
recognized along the Upper Missis-
sippi until during the progress Of the
present survey in the autumn of 1855.
The Medina sandstone and Clinton
group, which thin out to a great cx-
tent in the State of New York, have
almost entirely disappeared before
reaching Wisconsin. These forma-
tons are known only at one or two
points within that State, and thus far
have not been recognized in Iowa.
The Niagara limestone maintains
its character, and essentially its thick
ness, at the west. Extending from
Niagara falls through Canada, it forms
the peninsula of Cabot's head, the
Manitoulin islands of Lake Huron,
and the peninsula between Green Bay
and Lake Michigan and thence
| stretching southwcsterly across Wis
consin, it forms an irregular cscarp.
mcnt which reaches the Mississippi
river below Galena in Illinois and
thence takes, with the same features
its course through Iowa, leaving or
both sides of the river some outliers
further to the north, forming the
Mounds
Above the Niagara group, and cor
responding with it in direction, is ;
limestone formation of considerable
thickness, but which from its disturbed
condition, forms no conspicuous fea
ture i'll the country. This limestone
forms the rapids of LcClairc, and is
probably the same rock as that dc
veloped in the vicinity of Gait IN
! Canada West.
The Onondaga.salt group, which Is
next in order nf sequence, and IN New
York succeeds the Niagara limestone
with thickness of one thousand feet
or more. has so thinned out, that il
Iowa it is not more than one hundred
and fifty feet thick.
! The strata in New York and the