Geology of Rock Island County

Geology of Rock Island County

The soil of the Rock River and Meredosia bottoms is the rich alluvial deposit that is found in the neighborhood of all streams in this part of the Mississippi basin. The small portion of the county lying north of the bluff line is level sand prairie. This level stretch assists the imagination in calling up a vision of a mightier Mississippi than the one with which the earliest inhabitants of the valley were acquainted. In those earlier ages of the earth’s history when the river divided at this point with its main channel in the slough and Rock River bed it was miles in width. This prairie was a broad headland and bar. The bluff buttressed upland of the northern county was a noble island rising from the waters of the swiftly rolling, magnificent river. The sand brought down by the cur-rent lodged against the head of this great island and the sand plain was slowly formed, just as the bars are now being formed against every obstruction in the river in these days. This great stream which has left its history written on bluff and bar and pictured in sculptured bedrock and drifted cairn has no more perfect record than its old shore line marked high along its bluffs. The town of Cordova is built almost entirely upon a terrace which was once the bed of the river. This terrace is fifty feet above the present low water mark of the Mississippi. This reminder and evidence of the ancient river’s majesty can he traced along the slough and Rock River bluffs until that river empties into the Mississippi. Evidences of glacial drift are almost absent in this county. Genuine drift gravel and boulders are scarce. The soil of the bluffs and hills is a many deposit known as “loess” which overlies blue clays and sands. Farther from the river the “loess” gives place to fine luminated drift clays such as cover most Illinois high prairies and upland barrens. The surface soil is underlaid by foundations of stone .of successive geologic ages. At the eastern end of the county near Hampton the upper and more shaley beds of the Hamilton limestone first appear in outcrop-pings along the Mississippi bank. Still heavier outcrops show near Moline. Here the stratum is thicker, is brown in color, and is fossil bearing. Farther west near Rock Island and Milan the Hamilton is thicker, bedded with more irregular stratification, the color bluish white or brown on recent fracture, and the rock of firm texture and density. The island in the Mississippi known as Rock Island is a great mass of this Hamilton limestone, chiseled into shape by the water, covered with comparatively thin soil and splendidly wooded. This island is rich in indications of primitive conditions in this section as it has stretches of forest that have been allowed to retain their natural beauty and charm. The Devonian limestone of this county have been divided by scientists for litho-logical reasons into three divisions namely: the upper, the middle and the lower; each marked by its distinguishing characteristics. The upper-most division is limestone of gray or brown color, is rough and coarse-grained, and filled with the shells and corals that mark the Hamilton beds. The deposit is from thirty to forty feet in thickness. The middle division is made up of argillaceous and calcareous shales of equal thickness, this rock being filled with characteristic Hamilton fossils. The most easily noted outcropping of this division is between Rock Island and Moline where in quarrying a perpendicular space of thirty feet has been exposed. Under this division lies the third division which consists of a fine grained compact stone, of gray or dove color. This extends below the river level and is of an unknown thickness. It has been penetrated by borings to the depth of one hundred and seventy-five feet. This Devonian limestone of the third division forms the bed of Mississippi and Rock Rivers in this region. Rock River from Milan almost to the Mississippi is paved with what seem to be massive blocks of this compact stone irregular in size and contour and worn to smoothness by the ceaseless flow of the rapid current. The depth of this lithic stream bed has not been determined. At Sears’ mill which formerly stood below Black Hawk’s Watch Tower, rock was quarried from the stone floor of the channel to the depth of twenty feet, and it is probable that they were only upon the upper surface of the formation. At Cleveland near the eastern line of the county this same rock appears in the bed of the stream, so that it is probable that the bed of Rock River in its course along and through Rock Island County is formed of the Hamilton limestone at times obscured and overlaid by a mud deposit made possible by irregularities in the formation and moderate river fall. The limestone of the Rock River bed shows few fossils. It is this same division of the Hamilton limestone that forms the bed of the Mississippi throughout the sixty miles that this stream washes the shores of Rock Island County on the north and west. It created the terrors for the early navigators by its “hog-backs” and rocky chains thrown across the rapids in their sixteen miles of declivity and rapid rush of the mighty current. From the City of Rock Island to the western border of the county there are but few places where the bed of the stream is so near the surface of the water as to cause trouble to the rivermen. It is an alternation of stretches of sand, mud and rocky bottom. At Andalusia excellent building stone has been quarried from this lowest member of the Hamilton group. The layers are comparatively thin. The stone is fossiliferous and of a dove or light blue color. Another limestone formation appearing locally that has added to the wealth of Rock Island County is the Niagara deposit which outcrops heavily from Cordova to Port Byron. A little south of Hampton it disappears beneath the outliers of the coal measures. At Cordova this limestone has a tough consistency and hornstone appearance, differing in these respects from the same formation as it appears farther north along the river bank. All the upland region of the upper county lying above Pleasant Valley is underlaid by this Niagara limestone. The upper soil and upland clay is cut through by the streams and in the beds of these small waterways the limestone appears. This Niagara limestone has been commercially valuable through its burning into excellent quicklime which is strong, white and pure. At Cordova and Port Byron there have been for many years extensive works for the manufacture of lime and this has found its way on its merits into the markets of this country. The Hamilton limestone has also been found very available for lime-burning and great quantities of this raw material have been converted into merchant-able lime. The limestone deposits of Rock Island County have furnished inexhaustible quantities of building stone to the quarryman and builder. Another lithic mine of wealth to the settlers of Rock Island County has been the deposit of sandstone which outcrops in the lower part of the county. For a half century a quarry in a ravine midway between Milian and Andalusia has furnished building stone or rock for heavy masonry. The stone is dark colored and iron stained and comes from a stratum about ten feet thick. This deposit seems to be available by removing the soil deposit at any point along the bluffs to the west line of the county. Near Copper Creek in Drury Township there is a quarry which has supplied the demand for this material for walls which has proved durable and reliable where it has been used. After many years of use it seems to be unaffected by the elements. The clays of the upper part of the county have been used for commercial purposes. There are unlimited deposits of material for the manufacture of drain tile and this has become an important industry at various points, the most important point for manufacturing and shipping being Carbon Cliff on account of excellence of clay and convenience to railroads. The vein of potter’s clay which also appears in this section of Rock Island County has been worked to advantage. There has been a pottery in successful operation at Hampton for many years. In this series of geological notes naturally belongs reference to a remarkable group of mineral springs known as the “Rinnah Wells” springs. They have been known from Indian days to have medicinal proper-ties and some of them were long ago improved by stone curbs and facilities for obtaining the water in perfect purity. The sediment of the water caused by natural or artificial evaporation is a whitish mineral salt of pronounced and rather agreeable soda taste. These springs have also been called the “White Sulphur Springs”, also the “Soda Springs” and through the similarity of the waters to those famous ones of Saratoga and their marked medicinal value it was prophesied years ago that a great resort would some day be built up near Andalusia. These expectations have so far been unrealized, the use of the waters having been limited to local converts to their good qualities. It may yet be that Andalusia with its romantic name and waters of healing may yet attract the attention of the world and that this beautifully located village may be the mecca of tourists and healthseekers.


Early Settlements of Rock Island County 


Source: Historic Rock Island County, pub. Kramer & Company, Rock Island, Illinois, 1908

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