The Otis, Independence, and Davenport limestones form a group called the Wapsipinicon, from its outcrop along the river of that name in Linn county. The remaining limestones of the Devonian are grouped together under the name of the Cedar Valley. These consist of limestones of various types, sometimes crowded with fossils, and sometimes destitute of any trace of ancient life. They occupy the western townships of the county.
THE CARBONIFEROUS
At the close of the Cedar Valley stage the sea retreated westward from our area, and Linn county became dry land. For long ages its rocks were covered with rich soils supporting a luxuriant vegetation, probably tropical in its aspect. We know that running water channelled this ancient land, for when at last in Pennsylvanian (Coal measure) time the land sunk slowly beneath the sea, there were deposited in such channels clays and sandstones, which perhaps are only remnants of wide sheets of similar deposits now removed by denudation. A mile and a half south of Marion (southeast quarter of section 12, Rapids township) a well twenty-three feet deep penetrated a bed of dark shale which carried leaf impressions of a number of ferns characteristic of the undergrowth of the Carboniferous forests. A third of a mile southeast of Lisbon, and again about two miles south of the same village, at Bertram at the east end of the railway bridge, and on the old county road between Cedar Rapids and Marion, are exposures of sandstone which in some instances contain fragments of the logs drifted from perhaps distant uplands and water-logged and sunk in these ancient sand beds. The Bertram outlier contains many rolled coral fragments and worn bits of shells of the Devonian, included in Carboniferous deposits, much as the same fossils may now be found in the river deposits of the present age in the sand bars of the Cedar.
MESOZOIC AND TERTIARY
For a succession of geologic ages our county, in common with eastern Iowa, seems to have remained dry land, for no deposits of the sea are found upon it. On both sides of the continent mountain ranges of Alpine height were uplifted, and during the immeasurable years worn down, grain by grain, to flat and featureless plains. But no deformations are recorded in our county history and the lands seems to have remained so low that little erosion was possible. We are permitted to conceive that over our savannas in Mesozoic times there roamed monstrous reptiles of strange shapes, such as are known to have existed in adjacent states. In the later ages of this era it is not impossible that during the great submergence which brought the Cretaceous sea over the Great Plains from the Arctic to the Gulf, including western Iowa, our area also may have been inundated and huge swimming reptiles such as are found in the deposits of Kansas and Nebraska may have disported themselves where now our rich farm lands lie open to the sun, while in the air featherless cold-blooded creatures larger than any bird winged their way on leathery pinions.
THE ASTOR HOUSE
Erected by John Young in 1839, Looking South The Second House in Cedar Rapids
COURTESY CARROLL'S HISTORY
During the millions of years which are included in the Tertiary ages Linn county was undoubtedly dry land. On our grass lands pastured a succession of strange and uncouth mammals evolving into higher and higher forms. Among these denizens of the county were probably herds of pig-like creatures, three toed horses little bigger than foxes, and ancestral monkeys swarming in the trees, for such are known to have existed in other states. But these chapters in the history of the county can not be written from any local records.