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Shelby County |
HISTORICALCHAPTER II. - GEOLOGY.In general, however, it may be said that Shelby county belongs to what is known as the drift area; that her soil is composed of the finely ground and pulverized rock material that was brought down ages and ages ago by the great moving sheets of ice known as the glaciers. These glaciers finally melted and the soil as we know it was deposited in the waters. Therefore, in the absence of a recent complete geological survey of Shelby county, the author of this work is obliged to content himself with what Prof. C. E. White, then state geologist, had to say of the county in a geological report published by the state in 1870. The important parts of his report follow: "The valley of the West Nishnabotna is a beautiful tract of sloping bottom land of an average width of about a mile and the banks of the stream are lined by narrow belts or clumps of trees. The valley of the Mosquito creek affords another fine tract of bottom land, but there is scarcely a shrub to be seen along its banks throughout its course in the county. Silver creek lies in the high, undulating divide between the former stream and the west Nishnabotna. Its valley is less deeply excavated and its bottom lands are wet and miry. The middle Nishnabotna and Whitted's creek both possess fine bottom slopes, bordered by general acclivities. Little clusters of trees line their banks at intervals, and at Cuppy's grove, on the former stream, a fine body of young forests occurs. "On Mill creek, in the northwest corner of the county, there is quite an extensive forest, containing about eighteen hundred acres. It is known as Galland's grove and is the largest body of timber in this region. The following is a list of the common trees found in Galland's grove, which embraces the varieties commonly found throughout this section of the state: Burr and red oak, red and common elm, butternut, hackberry, black walnut, ash, linden, iron wood, coffee-bean, also sumach, thorn apple, blackberry, gooseberry, grape and other undergrowth. It is a noticeable fact that the cottonwood trees are rarely met with in the native groves of the inland districts on the Missouri slope. Nor do these trees thrive any better when transplanted than any of the other varieties of forest trees. The encroachment of the timber upon the prairie under favorable circumstances, i. e., when the prairie fires arc checked, is almost incredible. Where we observe today a little outlying thicket of hazel and sumach--the pioneers of the forest increase--a few years hence, unless arrested by the devastating fires, a grove of thrifty saplings will have sprung up, and this process is repeated indefinitely, until the beautiful prairie slopes are converted into forest-clad ridges and sombre thicket dells, as wild and uninviting to the agriculturist as may anywhere be found. Indeed, the apparent scarcity of forests in these counties will be no real drawback to their rapid settlement--not nearly so great as would be the case were our prairies clothed with a heavy growth of trees, now that building lumber is as easily obtained as it is in any of the counties of central Iowa. And more than all, these vast meadows of unbounded fertility hold out inducements to the settler such as no forest-clad region can boast. "The post-tertiary deposits deeply cover all parts of the county, completely hiding from view the older geological formations which underlie the region. As in the counties previously described, these deposits include the drift and the bluff. The modified or gravel deposit of the drift is well displayed in Mill creek, in Galland's grove, where it is seen resting upon the blue glacial clays and is overlaid by the peculiar yellow bluff deposit. The sands and gravel are arranged in the most perfect order, presenting all varieties of stratification commonly observed in connection with these deposits and rest upon a thin stratum of hardpan, such as is not unfrequently found in connection with the blue clays, although it by no means forms a persistent feature in the stratigraphy of these deposits. The gravel and boulder deposits crop out in the sides of the valleys at a much less elevation than in Audubon county; at the same time the Bluff deposit is proportionately thicker than it is in the counties to the eastward. "In the northern portion of the county the drift deposits appear in one of the highest ridges in this region, recalling the great drift ridges of Sac and the counties along the eastern margin of the watershed where the accumulations, of coarse materials form the most prominent feature in the surface geology. The outlier on the northern border of Shelby county is merely a remnant of a formation that once occupied the entire region now embraced in the Missouri basin. The ridge is covered with boulders of granite, gneiss, quartzite and limestone, presenting a striking contrast to the smooth stone-less surface of the adjacent ridges composed of the fine material of the bluff deposit. "Building material is exceedingly scarce in the county. The surface deposit in the valleys may be found to answer for the manufacture of brick, but as yet no practical experiments of the kind have come to our knowledge; (Brick had already been made in Shelby county. -- Editor.) However, we can not doubt that the same success will be attended here as elsewhere in this section. The soil everywhere is of the most productive nature. The steeper slopes in the more broken sections will always afford excellent pasturage, or they may be easily clothed with groves. In the valleys the finest meadow lands are found and the uplands afford beautiful locations for farms." Professor White's geological report for 1870 has incorporated in it a record of the altitudes taken in the survey of the Mississippi & Missouri Railroad Company, showing the highest points on the line of this survey of interest to Shelby county people. These altitudes are as follows:
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