GENERAL GEOLOGICAL FEATURES OF MIN

NESOTA.

GENERAL GEOLOGICAL FEATURES OF MINNESOTA.

Granite and Metamorphic Rocks.- An extensive range of the primitive system of rocks is found in the north-eastern part of our State. Commencing in Canada these exposures stretch along the north shore of Lake Superior and entering our State, constitute what might be termed mountain ranges. The general trend of these ranges is from the north-east to the south west. They cross the Mississippi River at Sauk Rapids and again appear on the Minnesota River about the mouth of Red Wood River. Although sometimes termed a mountain by Geologists the elevation of the highest of these ranges does not exceed 2,000 feet above tide water. The breadth of this Granitic region is out of proportion to its elevation-considering it as a mountain-being about 60 or 70 miles. But its Botanical and Geological characteristics entitle it to be called a mountain district. Here are found many plants peculiar only to Alpine regions. Here are also found nearly all varieties of the Granitic and Metamorphic rocks.

This region, described so well by Dr. Owen and other geologists, in its general features, is one of no small importance to the resources of our State. Particular observations, which have as yet been but little practised, will undoubtedly bring to light many valuable facts. Copper, silver and iron have already been noted to a considerable extent about Lake Superior, yet we have good reason to infer that in comparison but little is known of the mineral wealth contained in these mountain ranges. Among the Metamorphic rocks overlying, and at times confused with the Granitic, valuable material for purposes of art will undoubtedly be developed,— such as slates, crystalline limestones, soapstones, serpentine, etc.

The region of these primitive rocks-(their actual exposure)-does not cover a very extensive country-consequently the agricultural resources are not materially affected except over comparatively a small surface.

Even in the region where these rocks are exposed the soil of the little valleys is rich. Yet the mineral productions will more than compensate for the agricultural defects.

Lower Silurian Rocks.-Perhaps the lowest, or oldest fossil-bearing rocks in the world are found in Minnesota. Hugh Miller says, "America is emphatically the Old World." He means in a geological sense. If this is the case, the fossils found in the Lower Sandstone are certainly the oldest vestiges of creation. The Silurian rocks, according to Dr. Owen's nomenclature, (which I esteem as the best,) may be considered as follows, proceeding from the primitive rocks upwards:

Not that I

Each of these natural divisions I propose to notice briefly. have much that is new or undiscovered in regard to them, but more for the sake of calling attention to what may be their economical importance.

1. The Lower Sandstone.-This covers a large area of our State. In all probability it extends northward to Lake Superior where it forms the long disputed "Red Sandstones" of that region. If such is the case, (and I think there are proofs which in addition to what Dr. Owen has presented sufficiently establish this fact,) these Red Sandstones of Lake Superior are really the very lowest members of the Lower Silurian. That fossils should be exceedingly scarce in these rocks is not wonderful. If they ever existed, and they probably did, the heat, and other chemical agents, and disturbing causes to which they have been subjected has changed them in character to such an extent that they appear almost like another formation of a different age.

The Lower Sandstone is highly fossiliferous-containing Lingulas, Orbiculas, Trilabites, Crinoidea, Orthis and one species of the Obolus. Its palaeontology therefore is highly important.

Lead, I believe, has not as yet been discovered in this Sandstone. But copper ore to a considerable extent has been taken out of it.

This formation is deserving of careful investigation in all parts of our State whenever it appears as a surface rock. As well on account of its containing the first types of organic beings, as of its mineral value. If as Dr. Owen suggests, the Red Sandstones of Lake Superior, and the Lower Sandstone of the Mississippi River are of the same age; "it must be admitted," to use his words, "to favor the view that they are of the same age of the Red Sandstones of Virginia, Maryland, New Jersey, Connecticut and Nova Scotia." This being once proven beyond a doubt, will lead to a vastly important practical matter. It will serve to guide the mi

her in his explorations after mineral wealth and will save him, many times, a needless expenditure of toil and money. These Sandstones of Virginia, etc., have generally heretofore been conceded as belonging to a period subsequent to the Carboniferous era. But if Dr. Owen's views are correct in none of the regions where these red sandstones occur, need search be made for Coal, or any of its associates, underlying them. They belong to the Lower Silurian date.

I have spoken of the Lower Sandstone as containing the earliest types of organic beings. Its age is equivalent to the Potsdam Sandstone, of New York-for a long time considered the oldest fossil bearing rock in the United States, if not in the world. The lower series of the Lower Sandstone in Minnesota in which fossils are found is perhaps of a still older date. A development of its pataeontology is therefore highly important in a scientific point of view. And I may add that as a general thing whatever encourages and advances science, however distant apparently, from anything practical, will in the end be of the highest practical value.

2. Lower Magnesian Limestone.—This is the most prominent rock in the southern part of our State. The majestic and beautiful scenery between St. Paul and Prairie du Chien is mainly formed by the Lower Magnesian.

To what extent this formation is valuable for purposes of art, and for its minerel contents is but imperfectly known as yet. Lead and Copper ores have both been found in it. As a general thing it is more favorably situated for the retention of mineral ores than the Upper Magnesian, which is so rich in lead. I have but little doubt from the descriptions already given of it by Dr. Owen, and others, that a thorough exploration would lead to the detection of a greater quantity of minerals than is at present presumed to exist there.

The fossils of the Lower Magnesian are by no means numerous, or easy of determination. Dr. Owen succeeded in identifying several species-of which he mentions a Lingula, three species of Trilobites, a Terebratula, an Orthoceras, a new species of Straporollus, two species of Pleurotomaria, and a Murchisonia.

The soil derived from this rock is generally of an excellent qualitybeing durable and quick, and well suited for nearly all kinds of crops. Experiment, however, in middle and Southern Minnesota proves this remark to be highly gratuitous.

3. White Sandstone. This is sometimes called the Upper White, or St. Peter's Sandstone. It is almost pure silex or quartz. There is but a trace of alumina and carbonate of lime in it, scarcely enough to interfere with its use in any of the arts. It has been but sparingly tested in the manufacture of glass; but treated in the same way as the "Linn Sand,"

by Dr. Owen, it produced a glass of similar quality. Compared with sand from Lanesboro', Mass., from which beautiful glass is made, I can discover no difference in the purity of the grains. I speak more particularly of the purer beds, of which there is an abundance in the vicinity of Fort Snelling. Some of the beds contain traces of iron.

To what extent this sandstone may be valuable, remains for experiment to solve. A pure Silex in such inexhaustible beds, in such a state of fineness, cannot help becoming a resource of immense value in the course of time.

As yet no organic remains have been found in it.

It is also devoid of minerals of any consequence. Mr. A. Godfrey, near Minnehaha Falls, however, has shown me some fine nudules of Bi sulphuret of Iron, (Iron Pyrites,) which he found in the sandstone near his house. These, if found in large quantities, would prove valuable.

4. Shell, or Blue Limestone.-This is the Limestone at St. Paul, and at the Falls of St. Anthony. It has been pretty well tested for architectural purposes at these places, and also at Fort Snelling. A careful selection is necessary, in order to get a durable material out of it. The quantity of lime it contains is not sufficient to render it very valuable for burning. However, there are some localities where it is said to be equal in that respect to the Alton Lime. I have seen such an one near the town of Faribault, in Rice County.

From some experiments already made, this Limestone promises to furnish an excellent Hydraulic Cement. Ultimate success in this will be a matter of high importance to our State. From an analysis made by Dr. Norwood of the middle section of this Limestone, I have been enabled to compare it with the analyses of numerous hydraulic limestones in different parts of the United States, with the satisfactory inference that it is well suited for hydraulic purposes. It only lacks the necessary experiments to verify, as I think, the truth of my conclusion.

I am not aware that minerals have ever been discovered of any value in this limestone.

It is replete with fossils, which indicate its age to be equivalent to the Black River and Trenton Limestone of N. Y., and in part, to the Blue Limestone of Ohio. Most of its fossils are familiar to Geologists; yet there are some species new and undetermined. These yet may be of importance to the palaeontologist. Its distinguishing fossil is the Leptæna some 15 species of which occur in it. Orthoceratites are exceedingly common, and the species numerous. Some of them are of an enormous size, measuring 9 or 10 feet in length !

As to its durability for building purposes, much depends on the selection. If some of the lowest beds should be taken out of the quarry, dressed,