corroded. I believe it to be identical with that at Cincinnati. I found it in a chasm not filled by other rocks, one hundred and fifteen feet thick; but the stone was nowhere seen to fill that space, or to be more than thirty feet thick III. Buff-colored limestone in distinct well formed layers, including many portions or masses of white calcareous spar, and imbedding few or no organic remains IV. Soft saccharoid sandstone, consisting of sharp angular, transparent, minute fragments of quartz, scarcely cemented. It sometimes contains calcareous matter enough to effervesce freely with acids. It is often almost perfectly white, though sometimes colored reddish or brown by iron; when it is thus colored, it is often more strongly cemented. Its close resemblance to common moist unrefined sugar (especially the better or whiter kinds of sugar) does not fail to strike every person who examines it. Although the texture is so loose that a specimen can scarcely be broken off without falling to the state of incoherent sand, yet this rock crops out extensively, and seems to stand the weather as well as other strata which are substantial enough for building stones. I suppose, by its great porosity, it scarcely retains water enough to heave it by frost sufficiently to disintegrate it. I did not find precisely the lower termination of this rock, but, from having seen nearly forty feet of it exposed, I have ventured to give that thickness to it in the section V. A portion not examined, probably similar to the lower magnesian limestone described next VI. Lower magnesian limestone, resembling the cliff rock, but differing from it, however, in being almost destitute of organic remains. The lower beds of this stratum frequently afford a good building stone. This stratum exhibits, in some places, alternations of thin layers of sandstone, and some layers of limestone perfectly oolitic in structure. It includes many nodules of chert of a chalky whiteness; it contains, also, veins of so bright a green color as to excite the idea of copper ore, but yielding no evidence of that metal when examined by a proper test. At the point marked "stone quarry," this rock has been quarried'for building in Prairie du Chien. It appears to dress very well, has an agreeable lightdrab color, and shows every evidence of durability It will be seen that the stone crops out beyond the soil at three different points upon the hill-side, A, B, and C. These out croppings are continuous, so as to form three continuous parallel lines for miles in length, and serve to divide the hill into zones, called “benches." When seen from the opposite side of the river, they appear exceedingly straight and well defined, and afford a singular feature in the picturesque landscape. VII. There is, upon the side of the river opposite to Prairie du Chien, a stratum of sandstone thirty feet thick at the water's edge, identical in character with that three hundred feet higher Total Feet. 115 20 40 40 190 30 495 Section No 3.-From the Blue Mounds to the Wiskonsin river. We have here attempted to represent two sections: one seen partly beyond the other. The nearer one is represented in darker shade than the farther one. The nearer and darker one is a section along the valley of two small streams; and the farther one is a section through the mound, and along the ridge or highest part of the bank of those streams. The outline of the darker section is marked by several barometrical stations, as follows: First, "435." This was the place of encampment, near the head spring of the Peccatonnica river; that number (435) is the altitude above the waters of the Wiskonsin at Arena. Second, "590." This is the dividing-ridge between the waters of Rock river and Wiskonsin river. Third, " 421." The top of the sandstone. Fourth, "132." In a deep ravine, the channel of a small tributary to the Wiskonsin river. Fifth, "31." The edge of a sandy plain, extending from the bluffs two and a half miles to the river. Sixth, "0." The Wiskonsin river at Arena. The town of Arena has a place on the maps, was once a post-office, and contained a single log-house, which has since been burnt down. I found only the ashes of the log-house, an empty cart, and a few suits of "squawpoles," (a nickname for Indian tent-poles.) Such towns are not uncommon in this region. Beginning at the top of the Blue Mound, and proceeding downward, this section presents the following strata : I. Siliceous beds of chert, hornstone, and other varieties of flint, in very large masses. Some of them, I should say from recollection, were thirty feet long, twenty feet wide, and ten feet thick. They are stratified, and lie almost or quite in contact; but show a disposition to the nodular form, by frequent vertical joints, and being variously interrupted. The structure is often cellular, and the cells lined with small quartz crystals, which give a rough appearance to the masses. Fossils are rather rare in this siliceous portion, but such as were found belonged to the cliff formation. This member of the cliff, which is usually found as a mere included layer of a few inches, is here developed to II. The cliff limestone, including lead ore III. The blue fossilliferous limestone, very thin, and in some places entirely wanting, or apparently so. I have assigned it no thickness. IV. Sandstone. The same as that described at Prairie du Chien. There is every evidence that this is identical with that on the Mississippi, for it may be traced continuously along the Wiskonsin from one point to the other. It is remarkable for having its upper surface at an exact and even plane, very nearly level. In an excavated area, where several ravines meet in the same valley, and with the eye at any point of the upper surface of this sandstone, all other points appear in the same plane like an emptied lake, leaving a line of ice to mark its original height; even where the rock is covered by earth, the vegetation changes so abruptly in sort and color, at the surface of the sandstone, that the line may still be distinctly traced. Feet. 410 169 In the section which we are describing are represented two outliers, Feet. We have 40 188 V. Alternations of magnesian limestone and sandstones I had little opportunity of examining this stratum, and cannot give its characters; it is probably similar to the corresponding layers at Prairie du Chien. VI. Sandstone.—Variable, and not well defined VII. Limestone, (probably magnesian.)-In thick, well-defined strata, very suitable for building, but of rather a dark, ferruginous color. At the edge of the sandy plain "31," it was lying on the hillside in very large tabular masses, two feet thick, and twenty or thirty feet in diameter, with sharp angles and edges; sufficient evidences of integrity, strength, and durability. In external characters, it resembled the harder specimens of the cliff limestone, but was destitute of fossils; in thickness, above water Total 3 190 1,000 The sandy plain of Arena is covered, next to the bluffs, with a forest of small timber. Near the river are several groves of small pines, of a peculiar species; and so constantly does the wind blow from the southwest, that these trees lean with great uniformity about five degrees in the opposite direction. At various places, also, in the open plain, the wind has taken such hold of the sand as to uproot the grass, and, drifting the dried sand continually forward, has formed broad valleys, terminated by a semicircular sand drift, ten or twelve feet high, at the northeast end. Through the middle of this drift is a narrow slit. As the sand-drift progresses, vegetation is buried and destroyed, and thus prepared to be in time uprooted by the persevering breeze, which, urging the drift forward, by carrying the particles over from the windward and depositing them to the leeward side, finally exposes and excavates the spot which was once most deeply covered. The sandy stratum (IV) gives rise to the alluvial sands of the Wiskonsin, and to those of the Mississippi; indeed, it seems to be nearly or quite destitute of mica or feldspar; and the clear, glassy particles of quartz, of which it is composed, sparkle in the sun like minute brilliants. That the quartz is pure and unmixed; that the angles of the fragments are sharp and unabraded; that the surface of the stratum is an exact plane, like the undisturbed surface of a liquid; are interesting problems for the speculative geologist. I have thus gone briefly through with the subjects of the altitudes and the sections, and have incidentally given such imperfect sketches of distinctions and external characters of strata as were necessarily observed in a very hasty search for their several boundaries and junctions, while taking their admeasurements; but I have not offered these sketches as in any degrce answering as substitutes for the more complete discriminations which may be expected in your report. It is true that a sixty days' labor can but begin such a task as this field offers; but from the numerous specimens which you have collected, and from your known skill in analysis, (that allimportant source of valuable knowledge,) I hope you will review and en large upon the subjects of which I have here done little more than exhibit their proximate proportions. III. THE ALTITUDES TAINS, OF TABLE-LANDS, HILLS, MOUNDS," AND MOUN DETERMINED BY BAROMETRICAL OBSERVATIONS.-WITH A In determining altitudes by the barometer, it is important (and almost indispensable, indeed) that there should be simultaneous observations, both at the place, the height of which is to be determined, and at some point not very remote, the height of which has been previously ascertained. This becomes the more necessary in a northern latitude, and in the autumnal season, when the changes of a stationary barometer are frequent and rapid. My efforts to obtain a co-laborer, either at Galena or Dubuque, were fruitless; and the observations of Dr. Engelmann, of St. Louis, although accurate in themselves, were at too great a distance. Under these circumstances, my mode of operating was to observe the barometer at some known point of reference, as the surface of the river; and, proceeding with as little loss of time as possible to the height, make my second observation. When this was done in a few minutes, the proximate height was presumed to be deducible from the results; but if from the time, or other circumstances, an atmospheric change of the barometer was suspected, the instrument was taken back to the first station; the point determined, and an equation made according to the result. When the distance from the height to the station to which it was to be referred was several miles, then intermediate stations were established, and the observations repeated both going and returning, noting accurately the time by a chronometer. This last method was taken to determine the height of Blue Mound above the Wiskonsin river. The distance is about fourteen miles. Starting from my camp at the head of the Peccatonnica, at the foot of the mound, early in the day, I observed the barometer every hour upon my journey, until in four hours I had reached the river, and suspended the instrument close to the water's edge. I then returned by the same route, and repeated the observations at the same stations. This would have indicated any progressive change, and pretty nearly its hourly rate. As it happened in that case, the change, if any, was very small; and I obtained not only the altitude of my camp, but of three intermediate points. These stations and their altitudes are marked on the "section of the strata from the Blue Mounds to the Wiskonsin river," at the figures "435," (the encampment,) "421," "132," and "31." After all, there were several heights, which, for the want of a stationary observer, I was unable to determine; that of the Platte Mounds was one of them. The accompanying table, or chart, scarcely needs an explanation. I have placed them in the order of their height, and this happens to be nearly in the order of their latitude; the elevations becoming greater in proceeding northwardly. The geological distinctions marked upon the diagram serve to afford to the eye a direct comparison of separate and local observations, as between Pike's Mountain and Blue Mounds, where it appears that the corresponding strata, cliff limestone, blue limestone, and sandstone, each occupies a higher place in the latter than in the former, even supposing the points of reference to be level; which they are not, by the fall of the Wiskonsin, from Arena to its mouth, rendering the difference still greater. Thus is furnished important evidence in reference to the dip of strata, that it is, partly at least, westward; other evidence showing that it is also southward, we are led to the conclusion that it is between south and west. A remark on the western use of the term "mound.” It was first very properly applied to the numerous artificial tumuli of a conic or flattened hemispheric figure, which abound more or less in every part of the region west of the Allegany mountains. It seems that in the "far west" the term has been promoted to the office of representing isolated natural elevations of a conical form, which, emerging from the elevated prairies of Wiskonsin and Iowa, rise above the general table of the country to the height of two hundred, to four hundred, or even to six hundred feet; and, as appears in this table of altitudes, one thousand feet above the contiguous streams. They are certainly seen at the distance of forty miles, and rising, as they do, from the monotonous line of the prairie, like distant islands seen on the ocean, they are perpetually calling back the wandering eyes of the traveller, who sees them sink as he recedes, rise as he approaches, change their apparent position as he insensibly winds his course, or vary their hues of dim distance as the atmosphere drops or dissolves its misti ness. Deceived by the term "mound," which should be mountain, some writer has denominated them "interesting antiquities." To be sure they are antiquities, dating as far back as the "transition" or "secondary" epoch of the creation. The elements of terrestrial magnetism consist simply of the force, power, or intensity with which the earth attracts the magnetized needle, and of the direction in which that force acts; but, from the vast importance of the horizontal or compass-needle, both in navigation and surveying, and from the facility of suspending and experimenting with the same, it is customary to estimate certain elements of the needle in that position, although it is seldom the direction (never in our latitude) in which, if allowed to move freely in all directions, it would place itself. The quantities sought to be measured are usually four: First. The declination, "variation," or direction of the horizontal needle, as it respects the true astronomical north or south points. Second. The force, or intensity with which the horizontal needle is attracted by the earth, and held in its direction: this is called the horizontal intensity. Third. The dip, or true course in which a needle, perfectly free to move in all directions, would finally rest and be held by the earth's attraction. Fourth. The force or intensity with which the needle, in the direction of the dip, is attracted by the earth: this is called the total intensity.* To avoid a circumlocution of language, the earth's attraction is named without expressing particularly the mutual attraction between the earth and needle. |