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Much of the surface of Middle island is composed of loose masses of a limestone, which is admirably adapted to the manufacture of lime. Occuring, as these masses do, of a convenient size, the labor of quarrying is saved, while the manufactured lime may be safely and conveniently shipped. The manufacture of lime, for the counties bordering on the lower rivers, may be safely and economically carried on at this point. Several kilns have already been burned upon the island.

Between Middle island and Forty Mile point, limerock appears at intervals, forming the bed of the lake. The rock was not noticed, at any place, to rise above the surface of the water, and although it is of a compact and regular structure, and well adapted for practical use, its submerged situation will effectually prevent its application to any useful purpose.

Limerock again occurs at the straits of Mackinac, and in the vicinity. It appears upon the island of Mackinac, together with Bois Blanc, Round and St. Martin's islands, as also upon the northern peninsula, north from Mackinac.

The island of Mackinac, which has a circumference of about nine miles, rises in rocky cliffs upon its easterly and southeasterly portions, very abruptly, to a height varying from one hundred and twenty to one hundred and fifty feet.

The site of the present Fort Mackinac is elevated one hundred and fifty feet above the water of the lake. Beyond the first elevation, upon which the fort is situated, there is a somewhat level plateau, which, however, rises gradually, until by a final and quite abrupt ascent the island attains its greatest elevation, being two hundred and nineteen feet. This final elevation, which is some. what conical, has a flat area of limited extent on its very summit, upon which, during the late war, Fort George, afterwards called Fort Holmes, was erected. This beautifully situated spot furnishes one of the finest views of the surrounding coast and islands that could be conceived.

The island of Mackinac is based upon limestone, with a very superficial covering of soil. This soil, in consequence of the large amount of calcareous matter which enters into its composition, possesses a fertility that a superficial examiner would scarcely ascribe to it.

The limestone chiefly consists of an irregular assemblage of angular fragments, united by a tufaceous cement. These fragments usually appear, at first sight, to possess a compact structure; but a more minute examination shows them to contain numerous minute cellules, sufficiently large to admit water, which, by the action of frost, subjects the rock to rapid disintegration. Portions of the rock may, nevertheless, be selected partially free from this difficulty, and which are possessed of sufficient compactness to render them of value as a coarse building stone.

Hornstone, striped jasper, imperfect hog-tooth spar, calcareous spar and fluor spar occur imbedded in the rock, although the latter is of very rare occurrence.

Limestone, of a similar character, constitutes the chief portion of Round island; but here the rock is more compact, and will prove less subject to disintegration than that before mentioned. It will answer a good purpose as a coarse building stone.

A range of somewhat elevated hills, of limerock, occurs upon the main land, northwesterly from Mackinac, commencing a short distance inland. One of these hills, known as the "Sitting Rabbit," presents an abrupt cliff, destitute of vegetation upon its southerly side. This rock is, without doubt, identical, in geological position, with that upon the islands last mentioned.

The low group known as the St. Martin's islands, are also com posed of a similar limestone.

The shattered and deranged condition of the rock upon the island of Mackinac, and its vicinity, gives the whole mass a pecu. liarly complicated structure, and has led to what is conceived to be an error respecting it. Thus the rock has been described as a conglomerate, destitute of stratification, a conclusion which would appear to have been drawn without a proper consideration of the facts connected with the subject. That the fragmentary masses, composing the main portions of the rock, have not been transported, is conclusively shown by the fact that the most delicate angles are preserved, a circumstance which could not have taken place had they been subjected to the action of water, before being cemented. A careful examination has shown that portions of the rock still remain, in which the relative position of the original lines of stratification are preserved for an extent of several rods; and on Round island the line of stratification was traced for a distance of nearly half a mile.

The rock in question no doubt occupies very nearly its original relative situation, and its present condition may be ascribed to an uplift of the strata, subsequent to the complete induration of the rock; a cause which is amply sufficient to account for the present appearances. The fragments thus separated have been imperfectly cemented by the gradual infiltration of calcareous matter, thus re-uniting the complete mass.

It is well known that portions of the sandstone in the southern counties of the state are shattered in a similar manner; but in this instance the fragments have not been re-united.

The old red sandstone, over a large area, in the vicinity of the Porcupine mountains of Lake Superior, has been similarly disturbed, and the portruded trap rocks, which occur in the immediate vicinity, afford a sufficient explanation of the causes which have been most active in producing it; facts which should not be

lost sight of in explaining the causes of the present condition of the rocks in the vicinity of Mackinac.

From the island of Mackinac to Little Traverse bay, rock does not appear upon the immediate shore of the lake, though hills based upon limestone, stretch at a distance, through the interior. These hills approach very near the head of the bay mentioned, where they attain an elevation of several hundred feet; and as a whole they probably constitute the most elevated and regular chain of hills on the peninsula.

On the easterly side, and near the head of Little Traverse bay, the lime rock crops out. It continues for a distance of nearly a mile, forming an abrupt cliff, elevated from ten to twenty feet.

This rock varies from a dark blue and compact limestone to that of a greyish color and sub-crystalline structure. The rock may be easily quarried, and portions of it will answer a tolerable purpose as a building stone. But much of it is of an inferior quality; for the dark blue limestone is subject to break into irregular fragments, while much of the grey rock is either too flaggy, or contains so large a proportion of argillicious matter in its composition as to render it unfit for use.

At a distance of from two to three miles westerly from the place of out-crop just mentioned, the rock again appears, in a continuous cliff, elevated from fifteen to twenty feet.

The inclination of the rock is here northwesterly. It continues for a distance of about three-fourths of a mile, when it dips beneath the water of the lake. This series of rocks no doubt overlies that last described.

The separate strata of this cliff, at its highest point, are represented, in a descending series, as follows, the rock being overlayed by about one foot of soil:

1. Silicious limestone almost partaking of the character of sandstone-nine feet.

2. A confused mass of broken fossils, chiefly incrinites and cyathophyllae, imbedded in clay-two inches.

3. Vesiculated chert, colored with iron-four to eight inches. 4. Flaggy limestone, mostly separable into layers varying from one-fourth of an inch to one inch in thickness; the laminea usually forming a small segment of a large circle-eight feet.

5. Bluish clay (having the odor and appearance of silt,) divided by septae into irregular masscs. It contains imbedded semicrystalline grains of iron pyrites, which has the appearance of coarse, golden, yellow colored sand. About four feet of this stratum appears above the surface of the lake, and it was estimated to extend four feet below, making its total thickness eight feet. This clay is underlayed by limestone.

The rock appearing in the cliff is, as a whole, of an inferior

quality for economical purposes, yet portions may be selected which would answer a very tolerable purpose as a building stone. Limestone was noticed, at intervals, forming the bed of the lake, as far south as the northerly cape of Grand Traverse bay. At this latter place it was last seen to rise above the surface of the water, attaining an altitude of from four to eight feet.

This rock contains large quantities of imbedded hornstone arranged in irregular layers, varying from two to twelve inches in thickness. The silicious matter having been deposited in thin successive layers, gives the whole mass of hornstone a beautifully zoned appearance.

Portions of the limestone rock will furnish a tolerably good material for use as a coarse building stone, but as a whole it is of inferior quality.

About four miles southeasterly from the lime rock last described, and just within Grand Traverse bay, a dark colored bituminous slate, containing nodules of iron pyrites, crops out, and continues at intervals for a distance of a mile. It closely resembles that before described as occurring at Sulphur island, near Thunder Bay, except that it is not so highly charged with bituminous matter. The rock is of no practical importance.

South from Grand Traverse bay to the southerly boundary of the state, rock was not seen, in place, upon the immediate shores of the lake, but it occurs at many points a little in the interior, one of which may be noticed as being immediately connected with the rock strata under consideration.

This limerock comes to the surface in a hilly region, lying between Pere Marquette and White rivers, (town fifteen north,) at a distance of from ten to twelve miles from the shore of Lake Michigan. The surrounding country, embracing between one and two townships, is composed of broken, conical hills, rising abruptly to a height varying from one to two hundred feet. From the bases and sides of these hills numerous beautiful springs of water are discharged.

The rock is mostly covered with soil, and its character is not well determined, but situated as it is, at a distance from the coast, and not near any navigable stream, it is at the present time of no practical value.

In connection with the subject under consideration, I would call your attention to the immense quantities of rolled pebbles of limestone which occur on the shores of Lake Huron, more particularly between Thunder bay and Forty Mile point. The shores are lined at short intervals with these small masses, consisting of the harder portions of the rock, which have resisted the action of the elements. These masses possessing, as they do, great uniformity of size, are admirably adapted for use in the construction of roads.

The coast is not unfrequently lined, many feet in thickness with these fragments, and so situated that vessels may be readily laden with them. Occurring in the form they do, the expense of pounding will be saved, and no preparation will be required to fit them for immediate use in macadamizing roads.

It is well known that great numbers of vessels annually pass down the lake "in ballast," and it is deserving of serious consideration whether sufficient inducement could not be given for the transportation of this material for use upon the roads in the vicinity of Detroit river.

The finer gravels have already been considerably used for gravelling walks, but I am not aware that any use has, as yet, been made of the larger stones which occur in such abundance upon the upper lake coast.

Tertiary Clays.

A large proportion of the rocks of the peninsula are overlaid by a series of beds of clay, sand and gravel, that sometimes attain a thickness of several hundred feet. These beds compose a group of deposites, the lower portions of which, so far as I am able to deterinine, are destitute of fossil remains. Some of the members of the group would appear to be of a local character, occupying but a limited extent, while others are spread over a large area of country. Of these deposites, perhaps no one occupies a greater extent than the lower clay, which is nearly universal upon the border portions of the peninsula.

The members of this group are most largely developed upon those parts of the peninsula bordering on the coast, and they gradually become thinner as we proceed inland, until they finally wholly disappear; their place being supplied either by rock in place, or by diluvial deposites.

The great thickness of the exposed portions of these tertiary beds, upon the northwestern part of the peninsula, afford ample opportunities for examining this interesting series of deposites. But since the consideration of the subject, as a whole, will be left to the future, a few allusions only will be made to some of the clays embraced in the series.

The lower clay, which is usually of a blue or bluish gray color, is almost universally more or less filled with imbedded pebbles, chiefly of primary rocks, which sometimes, though rarely, attain to several hundred pounds weight. These water-worn masses usually completely ruin the clay for all practical purposes, but in a few instances the clay has been found sufficiently free from them to admit of use for the manufacture of bricks. The thickness of this clay is known only at a few points; and as the deposite was made unconformably upon an unequal surface, its thickness must be subject to very great variation. In the vicinity of De

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