GEOLOGY. Minerals as an agency in the for mation of soils is an interesting study to the farmer. By it he may not only form a definite opinion as to the nature of the soil, by knowing what earths are produced by the decomposition of certain rocks, and the elements of which they were composed, and the study is interesting as showing the various agencies in nature used in the formation of soils, and especially in the for mation of western soils. Hon. James Shaw, of Illinois, some years ago, when more actively engaged than now in studies relating to the soil and soil uses, in an address before the Illinois State Horticultural Society, well and accurately elucidated the subject of geology, as relating to the origin and formation of soil, the district of country referred to being rich in various strata, and in its diversity of soil. Speaking of that part of Illinois lying north of the old Siluria. beach, which crosses the State from a poin near Hampton, north of Rock Island, on th( Mississippi river, and passes eastward, a few miles south of Ottawa, bending up a little north of Morris, and passing on to the eastern line of the State, south of Chicago, says: The land north of this Silurian beach was compara tively elevated table land at the time the coal deposits of the great coal basin lying south of this old beach were in process of formation. And there is evidence that over this comparatively elevated table land a great denudation has taken place. Some great force has worn off and swept away, from southern Wisconsin and Northern Illinois, a large amount of material, which has been deposited over the face of the country south and west of that elevated region. It is estimated by Prof. Whitney and other good geological authori ties, that at least 300 feet has been denuded and carried away in the region of the Illinois and Wisconsin mounds. These mounds—Scales mound, the Blue mounds, Terrapin ridge, and the various elevated and island-like elevations left over the general level surface of that part of the State north of this old Silurian beach the Mer de Glace, or sea of ice. Inasmuch as snow is constantly being added to it, the volume and thickness of this sea of ice would soon become so great as to produce serious consequences if some safety valve was not found to afford vent to the pent up mass. The lower part takes upon itself a slow, almost imperceptible motion, and soon fills the descending valleys with a stream or river of ice. As snow is added at the top, it sinks down to the bottom, and when it becomes ice, is drawn off, as rivers run out of lakes. This ice river flows slow, but is subject to all the laws of flowing water. It widens, it contracts, it deepens where the flow is slowest, and its motion increases where the mass passes over rapids. As it crawls down in its slow, irresistible motion, dirt bands are formed along its margins, stones and great masses of rock roll down upon it, the bottom and sides of the channel are grooved, planed and striated by the mighty power of the grinding, rubbing ice, and all the material accu mulated is carried eventually to the lower end of the glacier, and there dumped off in terminal moraines and huge piles of gravel, bowlders, and other drift materials. In the case of the Alps, the glaciers melt when they reach the plain and before they find the sea, and glacier-born torrents begin where the ice ends, and the materials borne thither by the ice are further moved and assorted by the muddy, rushing waters which take their place. The struggle of the snow-flake has ended, and the struggle of the rain-drop now begins. Both are trying to get back to their mother, the sea. It is true the ice river flows infinitely slow, but in comparison with the river of water it moves infinitely strong. The Mississippi, if it were a glacier instead of a water river, could bear upon its back bowlders and whole ledges of stone as readily as it now floats a feather or a saw log. What it lacked in motion, it would make up in the slow, irresistible and mighty force of its all grinding, all consuming procession. Such is a wlacier in the Alps, and these glaciers are knead ing certain parts of Italy over now as in past time they kneaded North America. Over the new Wrangell's Land and in Greenland the same forces of the ice are in active operation, only to a much greater extent. All upland Greenland is one vast liter de glace. But the Greenland glaciers, instead of melting in intermediate sunny valleys, push down into the sea itself, and after crawling along its bottom in the indenting bays and fiords, keep breaking off great masses, which float away in the deep blue waters until they are caught by wind currents and gulf streams, to be borne by them as icebergs and ice floes, whither the drift of the ocean carries them. And thus they float, until warmer seas cause them to melt in sunnier climes, and the floor of the ocean is strewn with their adhering dirt and stones. Certain iceberg paths in the sea already are accumulating at the bottom of the waters fields of bowlders and huge win drows and beds of gravel and dirt. Baffin's Bay, Hudson's Bay, and other northern seas and bays thus become nests of icebergs, and these icebergs before reaching the water, were glaciers, and these glaciers, at their origin, were the arctic snows of Greenland. Thus Greenland, like all other polar and circumpolar lands, is shipping her bowlders and her gravel to the bottom of distant oceans, and these, at some time in the future eternities of God, will become the face of continents. But we
will come down to the prairies of Illinois. Start ing with the bowlders in the neighborhood of Lake Superior, we trace them south and west to the Missouri river. These crystalline sandstones, flame colored granites and black-trap rocks, can be traced back to their parent ledges about the start ing point. As we advance away from the parent ledges, the bowlders become smaller, and the drift materials towards the Missouri river are only gravels and drift clays. On seeing these curious water-worn stones strewn over the face of the country, the most ordinary mind at once concludes that they did not grow there, but were brought there from some other place. They are nigger heads, lost rocks, wanderers away from where they originally existed. They are entirely unlike any rocks outcropping round them, or in that region, and it is no great task to trace back the track over which they came. The world was lately excited over the Cardiff Giant, but men went to work and soon traced it back thousands of miles to its original bed in the gypsum quarries of Fort Dodge. In the same way they trace the bowlders back towards Lake Superior and Greenland, and could find the origin of each one if a few thousand dollars, or a large humbug, were involved. In some parts of Iowa these loose stones, from the size of a man's fist to that of a shock of wheat, lie so thickly strewn over the ground and accumulate round the margin of the lakes to such an extent, that in the one case parties might walk over them, stepping on the bowlders alone; and in the other, they have given rise to the superstition or belief in, walled lakes. In looking over a field of these bowlders once upon a time, my companion, who was somewhat irreverent, exclaimed, that it seemed to him as if the devil, when he sifted the soils down out of his great sifter, had emptied with a jerk the accumulated stones over this particular field. If he had named the Creator, instead of his satanic majesty, I would have thought the comparison a good one. Now, I believe the ice cap which covers Greenland at the present time once extended down into the middle regions of North America. Agassiz, some years ago, demonstrated to the satisfaction of the scientific world, that a great ice cap did cover the drift regions of the American continent. The carboniferous summer slowly ended, and the glacial winter as slowly came on. An entire change of the flora and fauna of these parts of the earth took place. Glaciers covered our land in every favorable locality. Seas of ice accumulated in the basins. Stones were torn away from the outcropping ledges: ledges were ground into sand and clay; motion took place in various directions; but the general movement was towards the south and west. As the climate again grew warmer, the ice cap slowly melted, commencing at the south and melting the ice towards the north. Basins became filled with water, and lakes and seas existed, into which glacial-born currents of muddy water poured, and in which icebergs and floes floated, as wind or currents drove them. And we thus have the compound forces of the glacier, the iceberg, and the water torrent in vigorous operation. These causes, added to and coining after the peaceful agencies and influ ences, spoken of in the early part of these remarks, explain all that we see, while examining the drift formations, with which our Illinois rocks are covered. The peaceful causes which worked before the drift have also worked since the drift period, and produced some of the later phenomena observable. On pages 392 and 393 will be found a geological map of Iowa, Missouri, Illinois, Indiana, Ohio and Kentucky, and on pages 896 'and 397 a geological map of Minnesota, Wisconsin and Michigan, which will present a fair view of the geological forma tion of an important region of the great Missis sippi valley,. comprising as it does the great gram, grass and stock region of the United States. The explanation of the geological terms used are as follows: Alluvium. Deposits of earth, sand, gravel, and other transported matter, made by rivers, floods, or other causes, upon land not perm.neutly submerged beneath the waters of lakes or seas.
Tertiary. The first period of the mammals, or of the cenozoic era.
Cretaceous. Having the qualities of chalk; abounding in chalk.
Coal Measures. Strata of coal with the attendant rocks. Subcarboniferous. Carboniferous formation, the series of rocks (including sandstones, shales, limestones, and conglomerates, together with beds of coal), which make np the strata of the carboniferous are or period. The prefix Sub signifying under or below, and includes in the map the millstone grits.
Devonian. Pertaining to certain strata which abound in Devonshire, Eng.; of, or pertaining to their age or for mation.
Silurian. A term applied to the earliest of the Palaeo zoic ages, and also to the strata of the ago. The strati an Water-lime emdauniteotnwtool paleontological of top Silurian, Upper and Lower.
Metamorphic. Pertaining to, or exhibiting, certain changes which minerals or rocks may have undergone since their original deposition.
Triassic. Pertaining, or corresponding to the saliferons beds or new red sandstone of Great Britain. Eozoic—Azolc. The age preceding the existence of animal life, or anterior to the Silurian.
Igneous. Resulting from the action of fire; as lavas and basalt are igneous rocks. (See also article Soils.)