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EDITED BY John C. Parish
Associate Editor of the State Historical Society of Iowa
| Volume I |
November 1920 |
No. 5 |
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Copyright 1920 by the State Historical Society of Iowa
(Transcribed by Gayle Harper)
A GEOLOGICAL PALIMPSESTS
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Iowa is very, very old – as old as the hills, and older.
So old, in truth, is this fair land that no matter at what
period the story is begun whole eternities of time stretch
back to ages still more remote. Seasons without number have
come and gone Soft winds of spring have caressed a dormant
nature into consciousness; things have lived in the warmth of
summer suns ; then the green of youth has invariably changed
to the brown and gold of a spent cycle; and winter winds have
thrown a counterpane of snow over the dead and useless refuse
of departed life For some creatures the span of life has been
but a single day; others have witnessed the passing of a
hundred seasons; a few giant plants have weathered the gales
of four thousand years: but only the rocks have endured since
the earth was formed. To the hills and valleys the seasons of
man are as night and day, while the ages of ice are as winter,
and the mil lions of years intervening as summer.
Through stately periods of time the earth has evolved. Mud has
turned to stone, the sea has given place to land, mountains
and molehills have raised their heights, and tiny clams have
laid down their shells to form the limestone and the marble
for the future dwellings of a nobler race. Since the first
soft protozoan form emerged in the distant dawn of life,
myriads of types from amoebas to men have spread their kind
through endless generations. By far the greater number have
lived true to form; but a few have varied from the normal type
the better to maintain themselves; and slowly, as eons of time
elapsed, old species died and new ones came into existence.
Thus mice and mastodons evolved.
“All the world's a
stage" for the drama of life wherein creatures of every kind –
large and small, spined and spineless, chinned and finned –
have had ''their exits and their entrances" along the streams,
on the plains, among the mountains, in the forests, and on the
floor of the ocean. The theme of the play has been strife, and
all through the acts, be they comic or tragic, two great
forces have always contended. The one has aimed at
construction, the other has sought to destroy. The air and the
water were ever at odds with the earth, while the principal
objects of animal life have always been to eat and escape
being eaten. No one knows when the play began, no one knows
the end; but the story as told by the rocks is as vivid as
though it were written by human hand. This drama of life is
the history of Iowa before the advent of man.
The
record begins at a time when Iowa was under the sea. The only
inhabitants were plants and animals that lived in the water.
Very simple in structure they were: it was the age of the
algae in plant life while in the animal kingdom the noblest
creatures were worms. The duration of time that the sea
remained is altogether beyond comprehension. Slowly, ever so
slowly, the dashing waves crumbled the rocks on the shore and
the rivers brought down from the land great volumes of sand to
be laid on the floor of the ocean. Ten millions of years
elapsed, perhaps more, until at the bottom of the sea there
lay the sediment for thousands of feet of proterozoic rock.
This is the story as told by the Sioux Falls “granite" in
northwestern Iowa.
After a great while the sea over
Iowa receded. Then, for possibly two million years, the rocky
surface of the land was exposed to wind and rain. Over the
vast expanse of barren territory not a sign of life appeared.
No carpet of grass protected the earth from the savage attacks
of the water; no clump of trees broke the monotony of the
level horizon: the whole plateau was a desert. As the
centuries passed deep gorges were carved by the streams, and
at last the down-tearing forces succeeded in reducing the land
almost to the sea level.
Gradually from the south the
sea encroached upon the land until all of Iowa was again
submerged. Its history during the next ten thousand centuries
or more is told by sandstone cliffs in Allamakee County.
All sorts of spineless creatures lived in the water.
Crab-like trilobites swam to and fro, ugly sea worms crawled
in the slime of Cambrian fens, the primitive nautilus "spread
his lustrous coil" and left his "outgrown shell by life's
unresting sea", while jellyfish and sponges dwelt in quiet
places near the shore.
At last a new age dawned. The
all-pervading sea still held dominion over nearly all of North
America. So small was the area of land that the sand carried
away by the streams was lost on the bed of the ocean. The
principal upbuilding forces were the primeval mollusks that
deposited their calcium carbonate shells in the shallow arms
of the ocean. By imperceptible accretions the Ordovician lime
stones of northeastern Iowa were formed. Gradually the water
receded and the newly made rocks were exposed to the weather.
As the floods from summer showers trickled into the earth
during the ages that followed some of the minerals were
dissolved and carried away to be stored in cavities and
crevices to form the lead mines for Julien Dubuque. That was
millions of years ago.
Centuries elapsed while the
Iowa country was a desert-like waste. Then again the sea
invaded with its hosts of crabs, corals, and worms. Thousands
of years fled by while shell by shell the Anamosa limestone
grew. But as the world "turned on in the lathe of time" the
sea crept back to its former haunts and the land once more
emerged.
No longer was Iowa a desert. The time had
arrived when living things came out of the water and found a
home on the land. The ferns were among the first of the plants
to venture ashore and then came the rushes. Forests of
gigantic horsetails and club mosses grew in the lowlands.
Slimy snails moved sluggishly along the stems of leafless
weeds, while thousand-legged worms scooted in and out of the
mold. Dread scorpions were abroad in the land.
It was
the age of the fishes when the ocean returned and the process
of rock making was resumed. Endless varieties of fish there
were, some of them twenty feet long, and armed with terrible
mandibles. Enormous sharks infested the sea where now are the
prairies of Iowa. The crinoids and mollusks were also
abundant. It is they, indeed, that have preserved the record
of their times in the bluffs of the Cedar and Iowa rivers. He
who will may read the chronicles of those prehistoric days in
the limestone walls of the Old Stone Capitol.
Then
came a time when the climate of Iowa was tropical. Vast salt
marshes were filled with rank vegetation. Ugly amphibians,
scaled and tailed, croaked beneath the dripping boughs and
left their trail in the hardened sand as they fed on the
primitive dragonflies millions of centuries ago. Cockroaches
and spiders were plentiful, but not a fly or a bee had
appeared. Giant trees, enormous ferns, and ever-present rushes
stored up the heat of summer suns and dying, fell into the
water. As thousands of years went by, the reedy tarns turned
into peat bogs and slowly decomposition continued until little
but carbon remained. Such is the story the coal mines tell.
But the old earth heaved again, the Appalachian mountains
arose, and here and there a great salt lake or an inland sea
was formed. The supply of fresh water was exceeded by
evaporation and so at the end of a long period of time only a
salt bed remained or an extensive deposit of gypsum. So it has
come to pass that in the age of man stucco comes from the Fort
Dodge gypsum mines that were prepared at the end of the
Paleozoic era.
Enormous segments of geologic time
elapsed during which the sea had receded and Iowa was exposed
to erosion. At first the climate was arid so that plant life
was scarce, but as humidity increased vegetation developed
apace. In the animal kingdom the reptiles were dominant.
Crocodiles, lizards, and queer looking turtles were here in
abundance. Gigantic and ungainly monsters called dinosaurs
roamed over the land, while from the flying Jurassic saurians
the birds were slowly evolving.
During countless ages
the wind and water were engaged in their persistent work of
destruction. Gradually the land was reduced to the sea level
and the ocean crept in over Iowa. This time the water was
muddy and shale and sandstone resulted. As sedimentation
progressed great marshes appeared by the seashore and finally
the ocean receded, never again to encroach upon Iowa. In the
west the lofty peaks of the Rockies were rising.
Permanently disenthralled from the sea and possessed of a
favorable climate Iowa became the abode of the flora and fauna
of Tertiary times. To the east the Mississippi River probably
followed its present course, though its mouth was much farther
north, but the streams of interior Iowa were not in all cases
where we find them at present. The valleys were young and the
drainage was very imperfect. Luxuriant forests of oak, poplar,
hickory, fig, willow, chestnut, and palm trees covered the
hills, while moss-mantled cypresses grew in the marshes. There
were flowers for the first time in Iowa, and with them came
the bees and the butterflies.
The ancestors of squirrels
and opossums busied themselves among the branches while below
on the ground there were creatures that took the place of
beavers and gophers. Giant razor-back swine and something akin
to rhinoceroses haunted the banks of the streams. In the open
spaces there were species that closely resembled cattle, while
from others deer have descended. An insignificant creature
with three-toed hoofs passed himself off for a horse. All
sorts of dog-like animals prowled through the forests and
howled in the moonlit wastes. Stealthy panthers and fierce
saber-toothed tigers quietly stalked their prey, while above
in the branches large families of monkeys chattered defiance
to all. Bright colored birds flitted in the sunny glades or
among the shadowy recesses. Snakes, lizards, and turtles
basked on half-submerged logs or fed upon insects.
The
majestic sweep of geologic ages finally brought to an end the
era of temperate climate in Iowa, and after hundreds of
thousands of years ushered in the era of ice. It may have been
more than two million years ago that the climate began to grow
rigorous. All through the long, bleak winters the snow fell
and the summers were too cool to melt it. So year by year and
century after century the snow piled higher and higher, until
the land was covered with a solid sheet of ice. The plants and
animals suffered extinction or migrated southward.
As
this ponderous glacier moved over the surface of Iowa it
ground down the hills and filled up the valleys. Slowly the
ice sheet moved southward, crushing the rocks into fragments
and grinding the fragments to powder. At length there came a
time when the climate grew milder and the ice was gradually
melted. Swollen and turbid streams carried away the water and
with it some of the earth that was frozen into the glacier,
but much of the debris was left where it lay. Even with the
slow movement of glaciers, still there was time during the ice
age for huge granite boulders to be carried from central
Canada to the prairies of Iowa.
The first glaciation
was followed by an interval of temperate climate when
vegetation flourished and the animals returned as before. But
the age of the glaciers was only beginning. Again and again
the ice crept down from the north and as often disappeared.
Twice the glacier extended all over Iowa, but the three other
invasions covered only a part of this region. Rivers were
turned out of their courses. At one time an ice sheet from
Labrador pushed the Mississippi about fifty miles to the
westward, but in time the river returned to its old course,
and the abandoned channel was partly appropriated by the
Maquoketa, Wapsipinicon, Cedar, and Iowa. Again, as the ice
retreated great lakes were formed, and once for hundreds of
years the waters of Lake Michigan flowed into the Mississippi
along the course of the Chicago drainage canal.
The
earliest glaciers laid down the impervious subsoil of clay
while the later ones mingled powdered rock with the muck and
peat of the inter-glacial periods to form the loam of the
fertile Iowa farms. Probably a hundred thousand years have
fled since the last glacier visited north-central Iowa, but
the region is still too young to be properly drained, so
nature is assisted by dredges and tile. It was during the
glacial period that mankind came into existence, but no man
trod Iowa soil until after the last glacier was gone. Compared
with the inconceivable eons of time since the first Iowa rocks
were formed, it was only as yesterday that the ancient mound
builders flourished.
Such is the geological history of
Iowa. No one can say when the first record was made, but the
story through all of the ages is indelibly carved in rock by
the feet and forms of the mummied dead that He where they
lived. Age after age, as the sea and the land contended and
the species struggled to live, the drama of the world was
faithfully recorded. Sometimes, to be sure, the story is
partly erased, sometimes it is lost beneath subsequent
records, but at some place or other in Iowa a fragment of each
act may be found. The surface of Iowa is a palimpsest of the
ages.
JOHN E. BRIGGS |
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