(b) At Rinshed's Lime-kiln. Nearer the river, at Rinshed's kiln, the underlying sandstone can be seen. In this section there is exhibited either a fault or an instance of unconformability in the bedding. The relation of the sandstone to the limestone may be best exhibited by the following diagram: Diagram showing the relation of the Limestone to the Sandstone, at Ottawa, Le Sueur County. Kiln Explanation. a. Horizontal layers of white crumbling sandstone showing oblique sedimentation; sedimentation undisturbed, seen 25 feet. b. Interval of ten feet hid by debris. C. One bed of fawn-colored limestone, almost free from sand; lies below the stone of Rinshed's quarry, 2 feet. About ten rods below this kiln, near another old kiln built by excavating in the sandstone along the bluff, the following section may be seen: (c) Ten rods below Rinshed's Lime-kiln. No. 1. Limestone, fawn-colored, in undulating beds; beds two or three inches or as thick as one or two feet, apparently disturbed...... ... 15 feet. No. 2. Sandstone, as at Rinshed's kiln, undisturbed, seen...... 25 feet. Just back from the bluff where the last section was taken, is the opening that furnishes stone for the kiln. The lime stone here appears like that at the bluff. The whole of these exposures make up, in general, one irregular stratum of limestone, with sandy patches and layers occurring indiscriminately, and should not be divided generally into different members. The sandstone underlying, however, has an uneven upper surface, due perhaps, to the violence of the latest sedimentation, instead of upheaval, before the deposition of the limestone. There is no other way except that of supposing a fault, or an instance of unconformability within the Lower Magnesian, to account for the position of the heavy bed of limestone exposed so far below the top of the sandstone at Rinshed's kiln. A little more than a quarter of a mile below Rinshed's kiln, a little ravine crosses the beds, showing the upper portion of the sandstone, as follows: (d) Section in the Sandstone at Ottawa. No. 1. Red, hard sandstone, in one heavy bed, exactly like that in the cut on the Sioux City R.R. near Louisville..... 1 foot. No. 2. White sandrock, like that in the railroad cut near Louisville..... The observations made at Ottawa throw much light on the relation of the limestone there with that at Shakopee, thus Shakopee limestone Ottawa limestone. Jordan sandstone..=Ottawa sandstone. At St. Peter the quarry near the Asylum exposes the uppermost layers of the Shakopee limestone. Owing to the work going on in the finishing of the Asylum building, a fine opportunity is here afforded for seeing these beds in their best estate. The beds are here very regular, differing very much from the thin and confused bedding at Shakopee, and in the deep openings they seem to be all very heavy. Indeed, in the face of the quarry the bedding can hardly be discovered. It seems almost massive. Yet on quarrying the stone it parts along certain horizontal planes that must be bedding planes. Some faces show five feet. Other beds are two, and three, and four feet. The upper four feet are checked into beds of two to four inches by the weather. is rather darker, when first quarried, than the Kasota stone, but has the same general cast of color. It seems sometimes to have a brownish tinge. The amount seen here is about twenty-five feet. It In the banks of the river at St. Peter, the sandstone, corresponding to that already described at Ottawa, can be seen, forming perpendicular or overhanging bluffs fifteen feet or more in height. On the terrace formed at St. Peter by these rocks, other quarries have been opened by Albert Knight, and by others, but none exhibit the characters of the formation so fully as that at the Asylum. Across the river from St. Peter, and about a mile toward Kasota, is another exposure of the limestone, in a bluff along the roadside. It seems here to be more shattered and irregular, and like the Shakopee stone. Lime burned near here cannot be distinguished from the Shakopee lime. About eighteen feet are seen, the lower part being in good heavy beds. The upper surface is waterworn, and in the openings the Cretaceous has been deposited. Geo. C. Clapp's lime kiln and quarry are five miles below Mankato, on sec. 17, township of Kasota, within the main drift bluffs of the Minnesota, but on the terrace formed by the Shakopee limestone, and about a mile from the river. His quarry, located near his kiln, exposes a fine gray limestone, about two feet thick, sometimes less or more, graduating into the Shakopee stone which underlies. It is very firm, little porous, and contains Orthis, at least, and affords the finest and purest limestone hitherto seen in the Shakopee stone. It must be regarded as the upper portion of the Shakopee. This fine, compact texture, and gray color, are not continuous in the same horizon, in other places the harsh magnesian grain and arenaceous quality existing in the same beds. Running along the river for several miles, sometimes touching the river and sometimes exposed back of islands that show the same, this limestone forms a bluff of solid beds. Although there is usually a heavy talus covering the foot of this bluff, yet at several points the identity of this horizon with that at St. Peter, and hence with that at Shakopee, is fully established by the exposure of the underlying sandstone. It is seen at a point about two miles below Mr. Clapp's farm. This bluff shows a good stone, as at St. Peter and Kasota, but is not much quarried. Perhaps it is more arenaceous in patches. It is blotched with whiter spots, and with soft chert. Another fine exposure of this geological horizon is visible about a mile and three quarters below Mankato, on the same side of the river. The place here referred to is that sometimes known as Hurricane Bend, although the point so named by steamboat captains is said to be about four miles further down the river. The section here exposed is the same as at Clapp's, and also the same as at Mankato, but here there is an observed thickness of sandstone amounting to forty-five feet, somewhat hid by debris. This equiv alency is unmistakable, since the bluff can be traced nearly all the way to Clapp's, and since between here and Mankato, besides the continuance of the same surface features-the wide, stony prairie formed by the terrace, the uniform altitude of the terrace, and its striking similarity to the terraces at St. Peter, Kasota, Ottawa and Shakopee-the actual continuity of the formation can almost be traced out by exposures of the rock. In the report of progress for 1872, the section at Maxfield's quarry at Mankato was given, (p. 83,) covering 61 feet of the Shakopee limestone. The further examination of this locality, and of the river bluffs for several miles below, during the season of 1873, makes it desirable to unite the sections observed in one general section, as follows: No. 1. No. 5. No. 6. No. 7. No. 8. No. 10. Section at Mankato, in Blue Earth County. ...... .......... 4-6 ft. 2-4 ft. 2 ft. 30 ft. Porous magnesian limestone, not used. ....... ..... ........ 4 ft. 10 ft. 2 ft. 3 ft. Lower shale bed; very much the same as the upper. No. 11. Jordan sandstone, seen about... Total of the Shakopee limestone, about...... 3 ft. 45 ft. 65 ft. From Mankato toward the mouth of the Blue Earth river, the Shakopee limestone is seen at frequent places, forming precipitous mural faces, capping the underlying sandstone; the two united making bluffs that rise from seventy-five to a hundred feet. These exposures are mostly on the right bank, but there are also elevated islands in the river, or at least elevated portions in the area of the bottom land, that present similar perpendicular rocky bluffs on one or more sides. These exposures extend somewhat beyond the mouth of the Blue Earth. The Blue Earth has cut its passage through this rim of rock, at the point of its debouchure upon the Minnesota bottom land, and on its right bank, at the place of the crossing of the St. Paul and Sioux City R. R., a series of interesting observations were made. Before reaching this point, however, in following the highway from Mankato to South Bend, but on the east side of the bridge over the Blue Earth, the Shakopee limestone is exposed in a recent excavation by the side of the road, in the removal of the Cretaceous clay, which is seen there to overlie it unconformably. The limestone here shows the effects of long exposure to the weather, and the action of water in the form of waves, probably those of the Cretaceous ocean, prior to the deposition of the clay. A much better example of the same effects may be seen a little further south, just before the crossing of the Blue Earth by the Sioux City R. R., where the grade is cut into the rock for several rods before reaching the river. The old Silurian surface is here very much weathered, and coated with iron peroxide, the nooks and openings, and all sheltered places being filled with the fine, plastic but bedded greenish clays of the Cretaceous age; the drift gravels and sands overlying both. These phenomena are alluded to again and more fully discussed under the head of the Cretaceous. Passing from the mouth of the Blue Earth south, toward the Red Jacket Flouring Mills, occasional exposures of the Shakopee stone are met with along the highway and in the railroad cuts (Minn. and Northwestern R. R.), for about three miles. The Red Jacket Mills are on the Le Sueur river, four miles south of Mankato. On the Maple, near its union with the Le Sueur, in sections 11, 12 and 13, township of Rapidan, (107, 27,) Blue Earth county, quarries that are feebly run, are owned by Barney Simmons, Samuel Michael, and by Messrs. Averill, Culver, Wood and Allgrain. These quarries reach about two miles above the mouth of the Maple, and are in the same horizon as the Mankato quarries. The stone occurs in horizontal, heavy beds, along the low banks of the river, exposing 25 or 30 feet. Some mention has been made of the Shakopee stone at this place in describing the sandstone there seen to overlie it, and supposed to be the St. Peter. (See p. 133). The Shakopee limestone is exposed at Garden City, in Blue Earth county, in the banks of the Watonwan river. Mr. S. M. Folsom owns a slight exposure which is somewhat worked, situated in the low bank of the river, near the water. At the milldam, just above the highway bridge, it may be seen, exposed in a rough and very irregular outcrop, in the midst of the river, forming a rocky island. It here |