PHYSICAL GEOGRAPHY

The following is taken from the GEOGLOGICAL SURVEY OF ILLINOIS, AND written by HON. JAMES SHAW:

Carroll County is situated in the northwestern part of the State of Illinois, and is bounded north by Jo Daviess; east by Stevenson; south by Ogle, Lee and Whiteside, and west by the Mississippi River. It contains an area of about 450 square miles. By surveys of the Illinois Central Railroad, its elevation above Lake Michigan is about 400 feet, and above the mouth of the Ohio River at Cairo about 800 feet. About one third of the count, the northwestern, is somewhat rough, being mineral or "lead-bearing" land. The surface of this is hilly and sparsely timbered, but in the valleys along the streams of this part of the county, many excellent farms have been opened. The usual alluvial bottom skirts the Mississippi, being from half a mile to four miles in width. Immediately adjoining the river there is a belt of heavy timber, but the rest of this bottom is composed of drifted sand banks, marshy swamps and rich tracts of the best pasture and farming lands. The southern and eastern parts of the county are composed of gently rolling prairies, with here and there an island-like grove, as if the fingers of the retiring ocean had stroked the soft surface into swelling undulations. The agricultural portions of the county are perfect garden spots-rich in their almost virgin soil and manifold resources of wealth. Nor is the county wanting in picturesque scenery. Carroll Creek flowing west through its center, and Plum River running through its mineral land, have each cut channels deep into the underlying rocks. These are piled about in massive grandeur-are crowned with evergreens; and are in many cases the abodes of wonderful echoes. Above Savanna, along the Mississippi River, the huge, towering Niagara rocks lift their heads like a Cyclopean wall
Geological Formation.-This country lies deep down in the Geological world, almost in the line of union between the upper and lower Silurian systems. Three distinctly marked groups of the rocks outcrop in Carroll County. These are the Galena Limestone, Cincinnati Group and Niagara Group. Above these are the usual deposits belonging to the quaternary system.
The Galena Limestone.-This is a massive grayish, yellowish or brownish drape colored Magnesian limestone-friable and coarse grained near its union with the clays, but very solid in its lower stratification, In Jo Daviess County it is estimated to be about 230 feet thick; in this county it has never been accurately measured, but is perhaps somewhat thinner, as we are on the edge of the lead basin. Its heaviest outcrop commences near the geographical center of the county. Thence, westward, heavy ledges of it outcrop along the banks of the Carroll Creek almost to Savanna. North of this little stream similar outcrops may be found, and the banks of Plum River. The former of these streams, especially, has cut it channel deep into this rock. Along this stream an anticlinal axis seems to run as the rocks dip slightly in both directions from the creek, and a slight upheaval must have once taken place here. Along the ridge of elevation thus formed, a fissure naturally would be left. The frost, the rains, and the tooth of old Father Time disintegrated, wore down and gnawed away the rocks, until the fissure became partially filled. This, in process of time, formed the little valley in which Carroll Creel now runs.
This is the famous "lead-bearing rock" of the Northwest. The ore occurs in fissures and caverns running through the rock in the form of what miners call "sheet" and "log," or crystalized mineral, the common sulphuret of led. In the reddish clay overlying the rock and formed by the decomposition of its upper beds' "float," ore is found, never, however, in very large quantities. Mining operations have never been carried on, on a large scale or on scientific principles. The diggings extend for several miles north and west of the town of Mt. Carroll. The pick, spade, common windlass and bucket are the only machinery in use. Little more than a livelihood has ever been made by these primitive miners. For a long time it was thought a system of deep mining would reveal heavy deposits of the ore. In two instances companies were formed and a considerable amount of capital invested. In one instance, water compelled the abandonment of the mine, and in the other nothing was found to repay a tithe of the expenses of the company. This surface mining will still go on as temporary employment for those whose other employments are not steady. But no one will probably be found willing to spend money enough to thoroughly test a system of deep mining. The deepest section of this rock measured by me is one hundred and fifty feet, but the bottom was not exposed and extended down indefinitely. The early writers have been treating the Galena limestone as a separate system. We believe it is now coming to be regarded as a member of the Trenton limestone, none of which latter rock outcrops in this county, although it is reached in sinking deep wells in the southeastern part, and one quarry of the real blue Trenton limestone is now worked in Ogle County, two or three miles from the county line. Of the characteristic fossils, the Receptaculities sulcata, or "Sunflower coral," of the miners is the most usually observed, and very perfect specimens are sometimes found. The Murchisonia obtusa and Lingula quadrata also abound. Orthocera several feet long, several species of the Orthis, corals of a number of species also abound. A very interesting species of trilobite has left its remains in these rocks, and we firmly believe that many new fossils will be found when the quarries in this rock are carefully and scientifically examined. Of the economic value of this rock we will speak again. It is the underlying rock in perhaps two thirds of the county, embracing the central, northern and eastern parts, being our chief building stone.
The Cincinnati Group-The gentle slopes from the Mississippi bottom lands up to where the bluffs are capped with the castellated crags of the Niagara Rocks, if exposed would reveal outcrops of this group. Some of the small streams have cut down into this formation through the overlying Niagara. Johnson Creek, winding in a sinuous course from the central to the southwestern portion of the county, shows the same rocks, sometimes near the surface. One half of the southern part of the county has this as the immediate underlying formation. About one mile below Savanna, there is a fine outcrop, where the county road cuts the side of the hills. About one mile above Savanna, there are considerable quarries opened in this formation on the side of the bluffs. Here the formation, as near as we can measure, is 80 feet thick. This is the best place in the county to make a selection. At some large springs just at the level of the Mississippi in a full stage of water the group begins resting solidly on the Galena limestone as a foundation. Far up the hillside the overlying Niagara rocks are just as distinctly marked. In the railroad cot on the Tomlinson farm, some four miles southwest of Mt. Carroll, may be found another and perhaps the finest exposure in the county. At Bluffville, also, it is exposed by quarries. There are, however, few natural exposures of this rock. It soon disintegrates and crumbles away. Gentle hills and slopes and graceful undulations are characteristic of its physical geography
Many springs burst out from the bases of these hills, and marshes and swampy places are not infrequent. Shales and shaley limestones compose a large part of the rocks of this group, but its lower beds are sometimes solid and massive enough for a building stone, and even contain lead in small quantities these shales are of a bluish-white color, their particles are finely comminute, as if deposited in deep, peaceful seas. A vast amount of carbon is contained in the black shales of this group. Specimens taken from near Savanna and from near the Beers Tomlinson farm, are almost as black as canned coal and burn with an oily, bright flame for a considerable time. Misled by this, some capital has been expended at the latter place boring for coal, and nothing but experience will convince those engaged that such a search is useless. One of our citizens also succeeded in extracting some oil, which he pronounced petroleum, out of similar specimans, When the great excitement arose in this country, an oil company was formed here, and but for the advice of the geologists, this company would now be spending its money in a vain effort to strike oil. The geologist of Iowa, Prof. Whitney, estimates that the carbon of these rocks, if gathered into one strata, would for a bed twenty-five feet thick.
Whence comes this mass of combustible in these old silurian rocks? No geologist, to my knowledge, has undertaken to answer this question. Is it of organic origin-the remains of an ancient vegetation? Is it the result of animate life? The Coral Halls Iowa Report states that no trace of vegetation has been observed in the widely distributed shales of this group, except a few traces of fucoids in the Utica slates of New York. This males him doubt the vegetable origin of this bituminois matter. In this county, however, we have discovered fucoids woven all over the tops of some of the strata in this formation. May it not be that a condition of things similar to that of the Carboniferous eras existed over the broad basin in which these shales were deposited? The vegetation consisted of the lowest orders-such as would decay and leave few traces of their existence. The disorganized remains would alone remain in the form of carbon, or coaly shale. The day may come when this substance, whatever it is, will be of economic value for light, or even fuel. With this brief notice, we must dismiss, for the present, this very interesting question.
This formation is prolific of fossils. Countless remains, with occassional perfect specimens of the splendid large trilobite, the Asaphus gigus are the most noticeable. Orthis occidentalis and I. O. lestudinaria abound. Some of these shales are covered with beautifully marked dendrites.Fucoids are also found. Orthoceratites and a large Lituites have been found in it, together with numerous other fossils.
The Niagara Limestone.-This is Owen's "pentemerus beds" of the upper Magnesian limestone. It is next in order above the group just considered. The traveller on the Upper Mississippi must have been struck with its bold and picturesque appearance, as he passed between Fulton City and Dubuque. Now the bluffs sweep down to the waters edge, now they trend off in a semi-circular direction, as if for the site of a colossal amphitheatre. Their bases indicate the gentle slopes of the Cincinnati shales, but their summits are capped with the Nigara rocks.
Like vast mural structures, they rise along the highest elevations, weather worn into all kinds of fantastic shapes, and displaying in their escarped cliffs resembles to old forts and ruined cathedrals, time-worn castellated battlements, or distant spires and minarets of some old town. Such is the appearance of these rocks along the river bluffs above Savanna. And towards the southern line of the county. The beholder, especially if he be a geologist, feels a strange spell stealing over him. Mighty visions of the old geologic ages enrapture his soul. A leaf from the old stone book is upturned before him, and he reads in the great Bible of Nature her sublime truths. He has discovered hard sense common sense in the rocks. But enough of dream and fancy sketching. Leaving the river, we do not find exposures of this limestone. Over the northern and northwestern portions of the county all the highest portions are covered with in, in broken fragmentary masses. Once it doubtless covered a large part of the county, but it has been denuded and carried off, leaving chert beds, corals and fragments of the rock itself, as memorials of where it once existed as the surface rock. The frost, the rain and the atmosphere pulverized the Niagara rocks, and the chert beds in them, being harder, settled down like a crop of white flints, sown over farm, field and hill. These chert beds show that the water of the old Niagara seas contained much silica in solution.
The Niagara limestone abounds in fossils. The most common and characteristic is the beautiful Pentamerus oblongus, or "pertrified hickory nut" of the miners. But the old Niagara seas were particularly the homes of the coarl builders, and those minute animals swarmed in countless myriads everywhere. Leaving their fossil monuments. Among the most characteristic are the Favosites, favosa, F. Niagerensis, Stromatop-oira concentrica, Haylsites, calenulatus, and many other species and genera, containing, doubtless, new and un-described corals.
This brings us through the Illinois rocks as developed in this county. Sometimes traces of the Trenton proper are found in the southern part, but they hardly deserve a place in the surface geology of Carroll County. The rocks of all three of these formations possess value as building stone. The Galena ranks first and the Cincinnati group last in economic value.
The Quaternary System-Alluvium. The Mississippi bottom, from Savanna to the south line of the county, in width averaging nearly five miles, is composed of this recent river deposit. The same deposit also exists north of Savanna on the Mississippi, and along some of the small streams in the interior. Some of it is a rich, deep black and rather wet soil, much of it consists of sandy deposits, while a portion forms our very best agricultural lands. The loess or bluff formation does not exist to a great extent in Carroll County, unless the soil and sub-soil of our productive prairies belongs to this deposit. Some of our bluffs, as, for instance, where Johnson Creek breaks through to the Mississippi bottom, are composed of the liess clays. The drift formation is also manifest in our county, to a considerable extent, although some seem to argue that it is undetected in the Galena lead basin. Deposits of drift in our county can be found resting immediately on the Galens rocks. All our little streams almost have cut down into deposits of boulders and gravel beds.
The following section, made in a well in the town of Mount Carroll, might be taken as a fair type of the superficial deposit resting upon our rocks, beginning at the top and measuring downwards.

Black prairie mold 2 feet
Yellow, fine-grained clay 13 "
Common blue clay 2 "
Reddish clay and gravel 15 "
Tough blue clay 2 "
Course, stratified gravel bed 2 "
Pure yellow sand bed 11 "
Black mucky clay 5 feet
53 feet

Another well, some three miles distant, passed through a second soil, some fifteen feet below the surface, and immediately thereafter a deposit of timber or wood, two or three feet in thickness, many of the pieces having tenacity enough to hold together for months after exposure to the atmosphere. This well is on the farm of Felix O'Neal, and at the time of its opening was considered and object of much interest.
We can not leave this part of our subject without again adverting to the boulders. For us they have a peculiar charm and interest. These "nigger heads" "hard heads," or lost rocks, abound in many places where the streams and rains have carried the soils away. Often times they are associated with gravel beds of the transported drift. Among them have been found several nuggets of copper, one of which was found lodged in a crevice of one our Galena quarries. Some of these boulders are striated and furrowed by the glacier or the iceberg. Quart, feldspar, granite, gneiss hornblende, porphyry syenite, and various combinations of these and other minerals of one of these lost rocks-real old cosmopolitans in a primal world. What a wonderful interest would cling around its wanderings from the time when it left its home among the Plutonic rocks of Lake Superior until some iceberg dropped it into its present bed, through gently-moving currents towards the southwest! Ocean streams rolled these uncouth stones for aged at the bottom of the "vasty deep." Frozen into glaciers, they have been pushed along their snail-like pace. Adhering to icebergs and ice fields and ice floes, they floated hither and thither through Northern seas, until the ice dissolved in its genial warmth. Could we know their true history, the masquerade of the elements, the lost history of the world, would be made as plain as a well-conned lesson. The associated pieces of water-worn copper are "finger board," telling from whence they both came, and the direction of the ocean currents which deposited our drift.