"Some slightly calcareous bands of this rock contain fragments of trilobites, and in numerous localities shells of Lingula are found. These fossiliferous bands appear in the vicinity of Lansing, where the bed containing trilobites lies some sixty feet above the river, In its general character this sandstone is a friable mass, usually crumbling on exposure to the frost and sun." "The passage of this sandstone into the overlying limestone is effected by numerous repetitions and alternations of the two rocks, giving rise to a series of beds along their junction, which from their chemical composition, might as well be reckoned to one rock as the other." Lower Magnesian Limestone. Of this formation, Prof. Hall says: "The great dolomitic mass which overlies the Potsdam Sandstone in the Valley of the Mississippi is known throughout that region as the Lower Magnesian Limestone. * * This rock becomes * a conspicuous member of the series where it forms the bluffs which overhang the Mississippi from Prairie du Chien far up the St. Croix. The undulations of the strata bring it to the surface in many valleys in Wisconsin where the Galena or Blue limestones occupy the elevated prairie (and this is also true on the west side of the river). Within the limits of Iowa the Lower Magnesian is most conspicious along the Upper Iowa River, it also crops out in the valleys of Paint Creek and Yellow River, but the amount of surface covered by it is quite small." * * * "The rock is usually checkered with seams and joints on its exposed surfaces, and presents a very rude exterior. In some localities, however, it will produce a durable building material." "The materials of the rock appear to have been broken up while partially indurated; the interstices are often filled with sand, and fragments of friable sandstone are often found mingled with the broken rock itself. In some instances these fragments bear evidence of having been torn from masses of rock previously indurated. In many cases the breceiated character seem to be due in some degree to internal action among the materials of the rock itself." In some regions, "sudden depression occur, where the succeeding rock comes in at a much lower level than it occupies on either side. The appearance is that of sudden small faults or downthrows, as if the rock over a certain area were abruptly depressed before the deposition of the succeeding one." "The annexed section on Bear Creek, near New Galena, thirteen miles due west of the Mississippi, shows the character and relations of this rock to the over and underlying sandstones. "Soft friable red sandstone... White crystalline dolomite, partly concealed, but showing itself at various points.... Beds of passage from dolomite to sandstone. White sandstone, to level of Bear Creek.. 12 feet .168 feet 30 feet 83 feet This shows "a thickness of one hundred and sixty-eight feet of the Lower Magnesian limestone, of which the lower one hundred and fourteen feet are concealed by a grassy slope. The upper fifty-four feet are exposed in a vertical cliff of hard white dolomite, irregularly stratified and somewhat concretionary in its structure. Of the upper-or St. Peter's-sandstone only twelve feet are here exhibited: it is a friable rock of red color." "The indications of the existence of organic life during the deposition of this limestone are few." Sulphuret of lead has been found in the Lower Magnesian in such quantities that formerly many persons were led to suppose that this rock might one day become of as much importance as the Galena limestone has been. We quote Prof. Hall: "The most important deposits of lead in this rock which have been observed within the limits of Iowa, are situated in the valley of Mineral Creek, a stream flowing north, through a valley lined with precipitous bluffs, into the Upper Iowa river, and about three miles south of a small settlement called New Galena: the diggings are on the southwest quarter of section 13, township 99, range 6 west. In this vicinity the Upper sandstone is well exposed on the top of the bluff, and a shaft has been sunk in it. Along the face of the bluff, in which a thickness of one hundred and twenty to one hundred and fifty feet of the Lower Magnesian limestone is exposed, a number of drifts have been extended into the rock, a little below its junction with the sandstone, and considerable galena has been taken out. The ore appears to be associated with irregular strings and bunches of calcareous spar, ramifying through the rock, but nowhere assuming a regular form like that of a vein, or appearing to occupy a well developed fissure. * * * * It is said that between fifty and one hundred thousand pounds of lead had been obtained from these diggings; but it seems hardly possible that the operation should have been, on the whole, a profitable one; and, we see little to encourage farther expenditures at this point." * * The "mine" was abandoned about that time, of which we shall speak further in another place; and although during the quarter of a century since then there have been a number of persons faithful to this idea of finding lead in paying quantities in the county, none as yet has been developed. Small quantities have been found from time to time, in various portions of the county -in Paint Creek, Jefferson, Ludlow and Union Prairie townships, on Portland Prairie, and notably in the valley of Yellow River and a small tributary three or four miles from the Mississippi. In the last mentioned locality specimens have been found as lately as 1881 which assayed 89 per cent. of lead, with 249.7 ounces of silver to the ton, and a trace of gold. Copper has also been observed in some of these specimens, as also in specimens from the New Galena region. Zinc deposits have long been known to exist in the vicinity of New Galena, and at this day there are parties prospecting with the purpose of developing its value and quantity. We quote further: "The Yellow River cuts into the Lower Magnesian, but not through it. At Volney this rock is seen rising in cliffs from the bottom of the valley to the height of thirty or forty feet. On the south side of the river, above the Lower Magnesian, may be seen cropping out the Upper, or * * * St. Peter's Sandstone.-"This rock occurs as a friable or incoherent mass, having a thickness of from fifty to eighty and even one hundred feet, and sometimes having so little coherence as to be removed from the bank like ordinary sand or gravel. Although the grains of which it is composed are of white or limpid quartz, the mass is often and particularly near the base, much stained by oxide of iron, while the upper portions are frequently quite free from discoloration, This sandstone will furnish an excellent material for glass making, whenever that branch of industry shall be established in the Mississippi Valley." This sandstone is found in many places in the county, and where accessible have proved very useful for building purposes as in the case of beds of it near Waukon. "It occurs in several outliers on the south side of the Upper Iowa River, some of them occupying considerable areas." On the banks of "the Mississippi the summits of the cliffs recede abruptly from the terrace formed by the Magnesian, owing to its less power of resisting denudation," but where the Trenton Limestone appears over the sandstone, the cliffs again assume their sharp outline above, though, "even then they present a recession above the Magnesian. Sloping abruptly from this, they are capped by the succeeding limestone which rises in perpendicular or overhanging cliffs. In consequence of this character the bluffs have the aspect of a double terrace, the first being formed by the Magnesian, and the second, some eighty feet higner, by the Trenton limestone." * * * * * * where it The Trenton Limestone, with its usual fossiliferous bluish-gray layers, occupies the elevated surface of the country through the center of this county, over a space of some ten or twelve miles in width. This rock is usually concealed by the superficial formations (drift, etc.), but crops out in the valleys, is quarried for lime and as a building stone, for both of which uses it is well adapted. The Trenton limestone proper is marked in some localities by numerous species of its characteristic fossils, while elsewhere they are extremely rare. This rock is mostly thin-bedded; though the drab-colored layers are firmer, thicker, and usually free from seams, furnishing building stone of moderate dimensions, and, rarely of the thickness of eighteen or twenty inches. * * * * * The increase in thickness is chiefly at the * * base of the formation." The limestones at the base of the Trenton, appear, from their chemical composition, to be better qualified to make good hydraulic cements than any others found in the State of Iowa. The following analysis will give an idea of the composition of the Trenton limestone as it exists in the northeastern corner of Iowa. The specimen is from a quarry four miles south of Waukon: "This is a very light drab-colored rock, not materially changing its color or appearance by weathering. It breaks with a smooth fracture into rectangular fragments. Its texture is finely crystalline, and it is very compact and homogeneous with the exception of minute specks of crystallized calcareous spar and bitumen which are sparsely scattered through it. It is in all respects a good building stone, splitting out in good shape, dressing easily and keeping its color well. This is not from one of the very fossiliferous layers of the blue limestone; but it contains a few fossils, and is colored by a trace of organic matter. "Insoluble (silicate of alumina).. Carbonate of iron.... Carbonate of lime.. Carbonate of magnesia, alkalies, chlorine, sulphuric acid and loss.. 4.07 .62 94.08 1.23 100.00 "The specimen analyzed above represents in character and composition the lower portion of the Blue limestone, as developed throughout the northeastern corner of the State. It is quarried in numerous places, and affords the best material, both for building stone and for lime, being an almost pure carbonate of lime. It sometimes fades slightly on exposure by the gradual disappearance of the organic matter which it contains; and is not unfrequently colored of a light buff on the exterior by the oxidation of the iron which it contains in the form of carbonate of the protoxide." "The passage from the Trenton into the Galena limestone above is not an abrupt one; on the contrary there are, in many localities, several alternations of calcareo-magnesian and purely calcareous layers between the two formations." The Galena Limestone is found in this county, only in the southern portions, occupying the surface of the elevated country south of the Yellow River. North of that stream a few outliers of this rock are found on the highest points, above the Trenton, but as we proceed northward these disappear entirely, and give place to the Trenton which occupies by far the largest portion of the surface of the county, south of the Upper Iowa, and is the most valuable rock we have, economically considered, because of its properties for building purposes, for lime and other uses; although portions of the Galena and the Lower Magnesian are also well adapted for building purposes. The Galena is the rock in which are found the valuable lead deposits of this State in the vicinity of Dubuque; but it does not appear in this county in sufficient thickness to warrant expectations of any future developments of value in that respect. Prof. Hall says: "The Galena limestone as usually developed is a rather thick-bedded, light-grayish or light yellowish-gray dolomite, distinctly crystalline in its texture and usually rather course grained, although occasionally so finely granular as to be almost compact." It "closely resembles in lithological character, as well as in chemical composition, the Lower Magnesian from which it is separated by the Trenton. It is, however, more uniform in its texture, and does not exhibit the breceiated and concretionary structure." It will be seen by those who are conversant with the geological system of this county, that while the survey by Prof. Hall twentyfive years age is substantially correct, he was not aware of the great irregularity in the various strata throughout the interior of the county which has since been developed in the shape of "faults", undulations, upheavals and other evidences of internal disturbances. In numerous instances "breaks have occurred in such manner as to show the entirely different formation of rock abutting upon each other, and side by side occupying large tracts of country on the same level, as in the case just northeast of Waukon, where a pure sand rock composes the entire surface, hills and valleys, on the east of an abrupt dividing line which separates it from a purely limestone formation. In this place it is appropriate to allude to Hon. Samuel Murdock's discovery of a fossiliferous rock underlying the Potsdam Sandstone. We quote from an article written by him in 1875. "From the neighberhood of Lansing there is a rapid southern dip in all the formations along the river, and this is so rapid that the whole thickness of one formation is entirely hid in the space of twenty miles, and this rate will correspond with the whole of them. Now if this dip was confined to any one of these formations alone we might conclude that it was originally formed at this angle, but when we see them all conform to the same dip and preserve a uniform thickness, it forbids the idea of an original slant. From the neighborhood of Lansing there is also a corresponding northern dip in all the formations, leaving the conclusion upon us, that somewhere in the neighborhood of this city, a powerful subterranean force is constantly being exerted to heave up a large portion of Iowa and Wisconsin, I am therefore strongly disposed to look to the new rock which I have recently discovered, lying beneath the Potsdam sandstone, as the great lever that is doing the work." "At the city of Lansing it rises to an altitude of more than two hundred feet above the level of the river, and can be traced to the water's edge, is largely composed of lime, and this substance in contact with both heat and water would furnish, perhaps, the |