The Redwood gazette. [volume] (Redwood Falls, Minn.) 1873-1940, 1881-01-27

granite abound. in some places enclosin,
masses of hOrnblende schist. For /:
miles, above Beaver Falls they fill tn,
whole valley. occurring ON each side o
the river. and rising SO 10 1875 feet abov,
it. Between Beaver and Birch Coole,
creeks the outcrOps ART mainly on tn,
north side of the Minnesota, rising in thei
highest portions 1OO feet above the river
Below the mouth of Birch Cooley the,
are mostly ON the south side, occurrin. ii
great abundance for two miles above an(
three miles below the mouth of w abashav
creek. The highest of these are a mil,
above this creek. rising Is to It's, or per
haps l4O feet. above the river It will bl
remembered that the bluffs along all thi.
part of the valley are about rs feet high
so that none If these lodges were visibl,
before the surface of the drift-sheet haC
been considerably channelled. At Bill
runs mill, on the Redwood river where
it enters the Minnesota valley, 1Lmiles
northeast from Redwood Falls, the rocb
is greenish talcose Quartzite, dipping
% deg. 8. E. One mile northeast from
this. on the opposite side of the Minneso
Ia and One-fOurth of mile north of the
ford. the rock is gray gnriss. weatherine
to reddish gray, apparently almost verti
cal. with its strike E. NJ E. At the cas-,
side of the road this gneiss is crossed by q
nearly vertical vein. to 8 feet vide, OF
ccarsely crystalline feldspar and quartz.
extending within sight 80 feet. These
strata are also exposed in the valley oil
Beaver creek one and two miles above its
junction with the Minnesota valley. The
Champion mill-dam ut the village of B.u
yer Falls is nearly within the line of strike
Of the gneiss described north Of che ford
and similar gneiss, with nearly the same
strike. is found here. Its dip is Is deg
is. ). E. AT the dam of the o. K. mill
one mile northeast from the last, is an
extensive exposure of gray gneiss, also
with E. n. E. strike; it is nearly vertical
or has steep dip to the s. s. E.. and in
some portions is mnch cOntorted. Veins,
. to IL inches wide. of cOarscly crystalline
flesh colored feldspsr. coincding with the
strike, are common here The valley OF
Birch Cooley, one mile above its ent rance
into that of the Minnesota, has a large
exposure of granite. holding interestinq
veins. faulted and divided portions o7
which are figured in Prof Winchell's re-.
port. One of these veins. composed OF
granite and four inches wide, is traceable
$50 feet. running southwest.
Two miles below the mouth of Birch
Cooley. a low outcrop examined OIL tho
north side of the river is granite. contain
ing. large proportion of flesh colored
feldspar. Lodges were next seen ON the
north side three miles below the last. in
the vicinity of the line between Birch
Cooley and Camp, extending half mile
westward from Reikie and Fenske's flour
mill. small outcrOp occurs Ave miles
southeast from these, besides a small
round lakelet in the bottom land north Of
the river. One mile farther southeast, in
the west extremity of Ridgely township,
and ~ miles west of Fort Ridgely are
the Lodges which supplied the stone used
in building The fort. An excavation
found near the north end of the outcrop
is in porphyritic granite. which contains
abundant gray feldspar crystals. a to *
inches long and one third or two thirds as
wide: i: also contains occasional masses
six to twelve inches long and half as wide.
mostly made up of black mica in small
grains. This ledge is also traverscd by
several flesh -colored feldspathic veins. 3
to inches wide. The other rock masses
near by are mostly feldspathic granite,
fcSh-cOlored. not motto ably pOrphyritic.
In one band here. the rock is hOrnOlende
schist and mica schist much contorted,
weathering to very rough honey connie
surface. This band extends several rods
from north to south, ami dips H deg. to
60 deg. w.
Very remarkable chemical changes have
taken place in the upper portions o. many
OF the exposures of gneiss anal granite
near Redwood Falls. The rock is trans
formed to a soft earthly or clayey mass,
resembling kaOlin. 1t has a blue or green
ish color, when freshly exposed; out VIII n
weathered assume a yellOwish ash color,
and finally becomes whit. and yli<,enng
Mica scales and lamin9 of quartz are gen
erall ! contained in this material, and have
the same arrangement as in gneiss, SO that
the dip can be Distinctly seen. Veins of
quartz or feidspar. the latter completely
decOmpOsed, and the lines of Joints, are
also noticeable. just as in granite or gneiss:
making it evident that this substance is
the result of decay of the rocks in their
original place. So far as can be Judged
from stream channels and other exposures.
this decomposition reaches in somv places
to depth of 20 or 30 feet. perhaps more
All grades Of change may BE- found, from
lodges where only herr. and there a few
spots have been attacked and slightly de-
composed. to portions where nearly evcry
indication of its origin has been obliter,.-
ted.
Before the extensive denudation of the
glacial period. it is propable that all the
granite and gneiss of this region were
covered by similarly decaycd surface.
Upon the areas where decompOsed rocks
still exist. the glacial plouyhing was shall
lower than elsewhere. These beds are
frequently overlain by crefaceous depos.
its. and appear to have been submerged
beneath cretaceous ocean. Prof. Win
chell suggests that their decay may have
taken place during this submergence, un
der the influence of the abundance of al
kaline chemical agents held in solution
by the sea in that age. Exposures ot
these kaolinized strata are found in RI.
vine north Of the river opposite MINI so.
ia Falls: in the gorge Of Redwood rive,
below Redwood Falls. interesting for its
grand and beautiful scenery; in many Of
the lodges of Minnesota valley for several
miles next below. especially in exposures
made by roads at the font of the bluffs
in the valley of Birch Cooley near its
mouth; and occasionally for or 10 miles
farther down the valley.