[Footnote: This lecture was delivered in the Chapel of the State
University, at Columbia, as an inaugural address on January 10, 1883,
and illustrated by projections. The author has purposely avoided the
very lengthy details of scientific observation by which the conclusions
have been arrived at relating to the former wonderful condition of
the Mississippi, and the subsequent changes to its present form: as a
consideration of them would not only cause him to go beyond the allotted
time, but might, perhaps, prove tiresome.]
By J. W. SPENCER, B.A.Sc., Ph.D., F.G.S., Professor of Geology in the
State University of Missouri.
Physical geology is the science which deals with the past changes of
the earth's crust, and the causes which have produced the present
geographical features, everywhere seen about us. The subject of the
present address must therefore be considered as one of geology rather
than of geography, and I propose to trace for you the early history of
the great Mississippi River, of which we have only a diminished remnant
of the mightiest river that ever flowed over any terrestrial continent.
By way of introduction, I wish you each to look at the map of our great
river, with its tributaries as we now see it, draining half of the
central portion of the continent, but which formerly drained, in
addition, at least two of our great lakes, and many of the great rivers
at the present time emptying into the colder Arctic Sea.
Let us go back, in time, to the genesis of our continent. There was once
a time in the history of the earth when all the rocks were in a molten
condition, and the waters of our great oceans in a state of vapor,
surrounding the fiery ball. Space is intensely cold. In course of time
the earth cooled off, and on the cold, solid crust geological agencies
began to work. It is now conceded by the most accomplished physicists
that the location of the great continents and seas was determined by
the original contraction and cooling of the earth's crust; though very
greatly modified by a long succession of changes, produced by the
agencies of "water, air, heat, and cold," through probably a hundred
million of years, until the original rock surface of the earth has been
worked over to a depth of thirty or forty miles.
Like human history, the events of these long _æons_ are divided into
periods. The geologist divides the past history of the earth and its
inhabitants into five Great Times; and these, again, into ages, periods,
epochs, and eras.
At the close of the first Great Time--called Archæan--the continent
south of the region of the great lakes, excepting a few islands, was
still submerged beneath a shallow sea, and therefore no portion of the
Mississippi was yet in existence. At the close of the second great
geological Time--the Palæozoic--the American continent had emerged
sufficiently from the ocean bed to permit the flow of the Ohio, and of
the Mississippi, above the mouth of the former river, although they were
not yet united.
Throughout the third great geological Time--the Mesozoic--these rivers
grew in importance, and the lowest portions of the Missouri began to
form a tributary of some size. Still the Ohio had not united with the
Mississippi, and both of these rivers emptied into an arm of the Mexican
Gulf, which then reached to a short distance above what is now their
junction.
In point of time, the Ohio is probably older than the Mississippi, but
the latter river grew and eventually absorbed the Ohio as a tributary.
In the early part of the fourth great geological Time--the
Cenozoic--nearly the whole continent was above water. Still the Gulf of
Mexico covered a considerable portion of the extreme Southern States,
and one of its bays extended as far north as the mouth of the Ohio,
which had not yet become a tributary of the Mississippi. The Missouri
throughout its entire length was at this time a flowing river.
I told you that the earth's crust had been worked over to a depth of
many miles since geological time first commenced. Subsequently, I have
referred to the growth of the continent in different geological periods.
All of our continents are being gradually worn down by the action of
rains, rills, rivulets, and rivers, and being deposited along the sea
margins, just as the Mississippi is gradually stretching out into the
Gulf, by the deposition of the muds of the delta. This encroachment on
the Gulf of Mexico may continue, yea, doubtless will, until that deep
body of water shall have been filled up by the remains of the continent,
borne down by the rivers; for the Mississippi alone carries annually 268
cubic miles of mud into the Gulf, according to Humphreys and Abbot. This
represents the valley of the Mississippi losing one foot off its whole
surface in 6,000 years. And were this to continue without any elevation
of the land, the continent would all be buried beneath the sea in a
period of about four and a half million years. But though this wasting
is going on, the continent will not disappear, for the relative
positions of the land and water are constantly changing; in some cases
the land is undergoing elevation, in others, subsidence. Prof. Hilgard
has succeeded in measuring known changes of level, in the lower
Mississippi Valley, and records the continent as having been at least
450 feet higher than at present (and if we take the coast survey
soundings, it seems as if we might substitute 3,000 feet as the
elevation), and subsequently at more than 450 feet lower, and then the
change back to the present elevation.
Let us now study the history of the great river in the last days of the
Cenozoic Time, and early days of the fifth and last great Geological
Time, in which we are now living--the Quaternary, or Age of Man--an
epoch which I have called _the "Great River Age_."
It is to the condition of the Mississippi during this period and its
subsequent changes to its present form that I wish particularly to call
your attention. During the Great River age we know that the eastern
coast of the continent stood at least 1,200 feet higher than at present.
The region of the Lower Mississippi was also many hundred feet higher
above the sea level than now. Although we have not the figures for
knowing the exact elevation of the Upper Mississippi, yet we have the
data for knowing that it was very much higher than at the present day.
_The Lower Mississippi_, from the Gulf to the mouth of the Ohio River,
was of enormous size flowing through a valley with an average width of
about fifty miles, though varying from about twenty-five to seventy
miles.
In magnitude, we can have some idea, when we observe the size of the
lower three or four hundred miles of the Amazon River, which has a width
of about fifty miles. But its depth was great, for the waters not only
filled a channel now buried to a depth of from three to five hundred
feet, but stood at an elevation much higher than the broad bottom lands
which now constitute those fertile alluvial flats of the Mississippi
Valley, so liable to be overflowed.
From the western side, our great river received three principal
tributaries--the Red River of the South, the Washita, and the Arkansas,
each flowing in valleys from two to ten miles in width, but now
represented only by the depauperated streams meandering from side to
side, over the flat bottom lands, generally bounded by bluffs.
The Mississippi from the east received no important tributaries south
of the Ohio; such rivers as the Yazoo being purely modern and wandering
about in the ancient filled-up valley as does the modern Mississippi
itself.
So far we find that the Mississippi below the mouth of the Ohio differed
from the modern river in its enormous magnitude and direct course.
From the mouth of the Ohio to that of the Minnesota River, at Fort
Snelling, the characteristics of the Mississippi Valley differ entirely
from those of the lower sections. It generally varies from two to ten
miles in width, and is bounded almost everywhere by bluffs, which
vary in height from 150 to 500 feet, cut through by the entrances of
occasional tributaries.
The bottom of the ancient channel is often 100 feet or more below the
present river, which wanders about, from side to side, over the "bottom
lands" of the old valley, now partly filled with debris, brought down by
the waters themselves, and deposited since the time when the pitch of
the river began to be diminished. There are two places where the river
flows over hard rock. These are at the rapids near the mouth of the Des
Moines River, and a little farther up, at Rock Island. These portions of
the river do not represent the ancient courses, for subsequent to the
Great River Age, according to General Warren, the old channels became
closed, and the modern river, being deflected, was unable to reopen its
old bed.
The Missouri River is now the only important tributary of this section
of the Mississippi from the west. Like the western tributaries, farther
south, it meanders over broad bottom lands, which in some places reach a
width of ten miles or more, bounded by bluffs. During the period of the
culmination, it probably discharged nearly as much water as the Upper
Mississippi. At that time there were several other tributaries of no
mean size, such as the Des Moines, which filled valleys, one or two
miles wide, but now represented only by shrunken streams.
The most interesting portion of our study refers to the ancient eastern
tributaries, and the head waters of the great river.
The greater portion of the Ohio River flows over bottom lands, less
extensive than those of the west, although bounded by high bluffs.
The bed of the ancient valley is now buried to a depth of sometimes a
hundred feet or more. However, at Louisville, Ky., the river flows over
hard rock, the ancient valley having been filled with river deposits on
which that city is built, as shown first by Dr. Newberry, similar to the
closing of the old courses of the Mississippi, at Des Moines Rapids and
Rock Island. However, the most wonderful changes in the course of the
Ohio are further up the river. Mr. Carll, of Pennsylvania, in 1880,
discovered that the Upper Alleghany formerly emptied into Lake Erie, and
the following year I pointed out that not only the Upper Alleghany, but
the whole Upper Ohio, formerly emptied into Lake Erie, by the Beaver and
Mahoning Valleys (reversed), and the Grand River (of Ohio). Therefore,
only that portion of the Ohio River from about the Pennsylvania-Ohio
State line sent its waters to the Mexican Gulf, during the Great River
Age.
Other important differences in the river geology of our country were
Lake Superior emptying directly into the northern end of Lake Michigan,
and Lake Michigan discharging itself, somewhere east of Chicago, into an
upper tributary of the Illinois River. Even now, by removing rock to a
depth of ten feet, some of the waters of Lake Michigan have been made to
flow into the Illinois, which was formerly a vastly greater river than
at present, for the ancient valley was from two to ten miles wide, and
very deep, though now largely filled with drift.
_The study of the Upper Ancient Mississippi_ is the most important of
this address. The principal discoveries were made only a few years
since, by General G.K. Warren, of the Corps of Engineers, U.S.A. At Ft.
Snelling, a short distance above St. Paul, the modern Minnesota River
empties into the Mississippi, but the ancient condition was the
converse. At Ft. Snelling, the valleys form one continuous nearly
straight course, about a mile wide, bounded by bluffs 150 feet high. The
valley of the Minnesota is large, but the modern river is small. The
uppermost valley of the Mississippi enters this common valley at nearly
right angles, and is only a quarter of a mile wide and is completely
filled by the river. Though this body of water is now the more
important, yet in former days it was relatively a small tributary.
The character of the Minnesota Valley is similar to that of the
Mississippi below Ft. Snelling, in being bounded by high bluffs and
having a width of one or two miles, or more, all the way to the height
of land, between Big Stone Lake and Traverse Lake, the former of which
drains to the south, from an elevation of 992 feet above the sea, and
the latter only half a dozen miles distant (and eight feet higher)
empties, by the Red River of the North, into Lake Winnipeg. During
freshets, the swamps between these two lakes discharge waters both ways.
The valley of the Red River is really the bed of an immense dried-up
lake. The lacustrine character of the valley was recognized by early
explorers, but all honor to the name of General Warren, who, in
observing that the ancient enormous Lake Winnipeg formerly sent its
waters southward to the Mexican Gulf, made the most important discovery
in fluviatile geology--a discovery which will cause his name to be
honored in the scientific world long after his professional successes
have been forgotten.
General Warren considered that the valley of Lake Winnipeg only belonged
to the Mississippi since the "Ice Age," and explained the changes of
drainage of the great north by the theory of the local elevation of the
land. Facts which settle this question have recently been collected in
Minnesota State by Mr. Upham, although differently explained by that
geologist. However, he did not go far enough back in time, for doubtless
the Winnipeg Valley discharged southward before the last days of the
"Ice Age," and the great changes in the river courses were not entirely
produced by local elevation, but also by the filling of the old water
channels with drift deposits and sediments. Throughout the bottom of the
Red River Valley a large number of wells have been sunk to great depths,
and these show the absence of hard rock to levels below that of Lake
Winnipeg; but some portions of the Minnesota River flow over hard rock
at levels somewhat higher. Whether the presence of these somewhat higher
rocks is due entirely to the local elevation, which we know took place,
or to the change in the course of the old river, remains to be seen.
Mr. Upham has also shown that there is a valley connecting the Minnesota
River, at Great Bend at Mankato, with the head waters of the Des Moines
River, as I predicted to General Warren a few months before his death.
At the time when Lake Winnipeg was swollen to its greatest size,
extending southward into Minnesota, as far as Traverse Lake, it had a
length of more than 600 miles and a breadth of 250 miles.
Its greatest tributary was the Saskatchewan--a river nearly as large as
the Missouri. It flowed in a deep broad cañon now partly filled with
drift deposits, in some places, to two hundred feet or more in depth.
Another tributary, but of a little less size, was the Assiniboine, now
emptying into the Red River, at the city of Winnipeg. Following up
this river, in a westerly direction, one passes into the Qu'Appelle
Valley--the upper portion of which is now filled with drift, as first
shown by Prof. H. Y. Hind. This portion of the valley is interesting,
for through it, before being filled with drift, the south branch of the
Saskatchewan River formerly flowed, and constituted an enormous river.
But subsequent to the Great River Age, when choked with drift, it sent
its waters to the North Saskatchewan as now seen. There were many other
changes in the course of the ancient rivers to the north, but I cannot
here record them.
As we have seen, the ancient Mississippi and its tributaries were vastly
larger rivers than their modern representatives. At the close of the
Great River Age, the whole continent subsided to many hundred feet below
its present level, or some portions to even thousands of feet. During
this subsidence, the Mississippi States north of the Ozark Mountains
formed the bed of an immense lake, into the quiet waters of which were
deposited soils washed down by the various rivers from the northwestern
and north central States and the northern territories of Canada. These
sediments, brought here from the north, constitute the bluff formation
of the State, and are the source of the extraordinary fertility of our
lands, on which the future greatness of our State depends. However, time
will not permit me to enter into the application of the facts brought
forward to agricultural interests. But although this address is intended
to be in the realm of pure science, I cannot refrain from saying a word
to our engineering students as to the application of knowledge of river
geology to their future work. The subject of river geology is yet in its
infancy, and I have known of much money being squandered for want of
its knowledge. In one case, I saved a company several thousand dollars,
though I should have been willing to give a good subscription to see the
work carried out from the scientific point of view.
I will briefly indicate a few interesting points to the engineer.
Sometimes in making railway cuttings it is possible to find an adjacent
buried valley through which excavations can be made without cutting hard
rock. In bridge building especially, in the western country, a knowledge
of the buried valleys is of the utmost importance. Again, in sinking for
coal do not begin your work from the bed of a valley, unless it be of
hard rock, else you may have to go through an indefinite amount of drift
and gravel; and once more, in boring for artesian wells, it sometimes
happens that good water can be obtained in the loose drift filling these
ancient valleys; but when you wish to sink into harder rock, do not
select your site of operations on an old buried valley, for the cost of
sinking through gravel is greater than through ordinary rock.
In closing, let us consider to what the name Mississippi should be
given. In point of antiquity, the Ohio and Upper Mississippi are of
about the same age, but since the time when ingrowing southward they
united, the latter river has been the larger. The Missouri River,
though longer than the Mississippi, is both smaller and geographically
newer--the upper portion much newer.
Above Ft. Snelling, the modern Mississippi, though the larger body of
water, should be considered as a tributary to that now called Minnesota,
while the Minnesota Valley is really a portion of the older Mississippi
Valley--both together forming the parent river, which when swollen to
the greatest volume had the Saskatchewan River for a tributary,
and formed the grandest and mightiest river of which we have any
record.--_Kansas City Review_.
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A catalogue, containing brief notices of many important scientific
papers heretofore published in the SUPPLEMENT, may be had gratis at this
office.
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