From the SP.

View of Castle Rock from the South-East.

There is another exposure of the St. Peter on Sec. 22, T. 114 N., R. 19 W., about a mile and a half west of Empire City, in Dakota county, within the river bluffs of the Vermilion, and on the north side of the immense slough that lies on that side of the river. It is somewhat quarried for foundation stone. The beds exposed are under about two feet of drift, and about twelve feet above the level of the slough. They lie horizontal. This indicates that the whole valley of the Vermilion, at that point, where it is said to have its greatest width, is wrought in that sandstone.

(d) THE SHAKOPEE LIMESTONE.

This limestone belongs to the great Lower Magnesian Formation, and is the uppermost member of it. In ascending the Minnesota valley its first outcrop is seen at Shako

pee, in Scott county, where it is wrought for quicklime. It is again exposed at Louisville, in the same county, five miles above Shakopee. A short distance above Louisville it recedes from the river, and the underlying sandstone, seen at Jordan, comes to the surface with a gentle dip to the N. or N.E., forming the "Little Rapids" in the river, and affording a useful building-stone at the quarries at Jordan. In turn this sandstone, by the same dip, is driven back from the immediate valley, and a lower limestone is seen, as at St. Lawrence, having different physical characters, yet belonging to the great Lower Magnesian.

At Ottawa and Kasota, as also at St. Peter, the Shakopee limestone has returned. It thence continues in the valley of the Minnesota, sharing its banks with the underlying Jordan sandstone, to Mankato, where a fine exposure of the beds of both may be seen. As the river there changes its direction it soon passes away from the area of the Shakopee limestone, although there are several fine outcrops on the Blue Earth, and on its tributaries the LeSueur, the Cobb and the Maple, as far south as the township of Rapidan. It is also exposed on the Watonwan, at Garden City, and gives rise, as at other places in the same township, to valuable mill sites.

This, in general, is the course of the Shakopee limestone. It has formerly been supposed to represent the whole of the Lower Magnesian, or For. 2 of Dr. Owen. Its thickness is about 70 feet. The underlying sandstone is about 50 feet thick. The thickness of the next member of the Lower Magnesian has not yet been made out. It is visible at St. Lawrence, in Scott county, and at Judson, in Blue Earth county. This, it will be observed, is not in keeping with the age given the Jordan sandstone by Dr. B. F. Shumard. He referred the sandstone at Little Rapids, and that underlying the limestone at Mankato, to For. 1, of Dr. Owen's series, which he made the equivalent of the Potsdam, of New York. The Lower Magnesian, however, in the bluffs of the Mississippi, at Winona, and at other points, is over wo hundred feet thick. In approaching St. Paul its thickness grows no less. It would be a singular phenomenon, to say the least, if at Shakopee, less than forty miles from Hastings where it has its full development, it should have become reduced to less than seventy-five feet. The existence of a heavy, calcareous formation below the Jordan sandstone, demonstrated by the observations of the past season, as detailed in the following pages, proves beyond all question

that the Jordan sandstone has been erroneously referred to the Potsdam age. The Shakopee limestone also maintains a distinct horizon in passing to the east. It was seen, in the season of 1872, at Quincy, in Olmsted county, and was mentioned in the report of progress for that year (page 82).

This assignment of the Jordan sandstone to the great Lower Magnesian formation is, on the other hand, in harmony with the reports of the Missouri geologists who describe that formation as made up of a series of alternating, yet constant, calcareous and arenaceous members. To what extent the lower part of the Lower Magnesian may be thus subdivided, and whether it corresponds to any extent with the Missouri subdivisions, it is not now possible to say.

Section at Shakopee, in Scott County.

No. 1. Can hardly be separated from the rest, but seems more shattered and thinner bedded. It also contains some chert. It is crystalline and porous, with no regularity of bedding......

No. 2. An irregular layer of sandstone, or of very sandy limestone, used for building stone, making some good faces; beds about 8 inches.....

....

...

No. 3. Rather heavier beds of hard grey limestone, of a magnesian texture and feel. These beds are sometimes cracked and checked in all directions, and pass into finegrained patches, and then thicken again. These thin beds are not infrequently wavy or contorted within the mass. Purgatories are also common in the face of the bluff through all the parts......

Section at Louisville, Scott County.

6-8 feet

2 feet

. 10-12 ft.

The quarry of Mr. G. Baptiste Contre shows a much disturbed and shattered condition of the layers, with frequent green stains as if of carbonate of copper. No constant general section of the bedding can be given, but the lower eight or ten feet are of a reddish color and in heavier beds. This quarry shows very evidently the effect of volcanic upheaval or disturbance. In general it bears a close resemblance to the stone seen at Shakopee. Twenty feet, more or less, can be seen. The quarry is in a bluff or terrace, facing the river, yet is separated from the river by another terrace of the same hight, made of the same layers of rock, facing away from the river. This latter rises as an island, about 30 feet above the river bottom.

The same rock is more or less exposed in the road from Shakopee, for a mile, before reaching Louisville. At Shakopee-and the same is true most of the way to Louisville

this limestone is the cause of a distinct terrace, which rises about 20 feet above the bottoms. On the surface of this terrace a great many boulders of northern origin, often remarkably large, are strewn, the close proximity of the rock preventing them from disappearing in the thin alluvium. As the direction of the river seems not to coincide with the direction of the strike of the limestone, it soon passes on to the belt of the sandstone seen in the Little Rapids, and at Jordon, the transition from the former stone to the latter being indicated by a change in the character of the river bluffs, and the terrace already mentioned. A short distance below the mouth of Sand Creek the limestone affords an exposure in the right bank of the river, while the creek itself is on the sandstone. The sandstone there is the only rock visible in the river, as far as to St. Lawrence, which is in T. 114, R. 24, Scott county. The limestone there exposed lies below the sandstone, and will be described in another place. With the exception of a slight exposure a mile or two below Belle Plaine, and another near Blakeley, the rock is not seen again on the east side until reaching White Rock Bluff, at Ottawa. On the west side, about a mile below the Jessenland Church, (Sec. 13, T. 113, R. 26) there is a low outcrop of the lower limestone in the river bottoms. 'At Ottawa, in Le Sueur county, the Shakopee stone has fully returned, and affords a very fine outcrop, rising, with the underlying standstone, to the hight of about 70 feet above the river, and causing as at Shakopee a broad terrace, on which the village stands.

Sections at Ottawa, Le Sueur county. (a)

No. 2.

John P. Rinshed.

Quarry of

No. 1. Fawn-colored, arenaceous limestone in even beds that correspond in undulations with the upper surface of No. 3. 4 ft. Sandstone with a calcareous cement; of a lighter color, and corresponding in undulations with the surface of No. 3......

No. 3. Magnesian limestone, very much like the Shakopee stone, holding green clayey deposits; in lenticular and irregular beds; the surface, freshly uncovered by the removal of the beds of No. 2, has much the appearance of being weathered, rising and falling at gradual angles and causing the overlying members to have corresponding undulations. Not well seen here. Said to be...

Total....

2 ft.?

8 ft.

14 ft.

Other quarries showing nearly the same composition of layers as Rinshed's, are owned by Levi Case and Charles Schwartz.