Box 15, Folder 3: Geology of Wisconsin 1869

15

The next or 13th formation, lying below the Lower Magnesian limestone, is another sandstone. It is different in some respects from that found above. It is usually more pure, being apparently an aggregation of pure clear quartz crystals without apparent cement of any kind. Upon exposure to the weather the cohesion of the particles is destroyed, and the rock crumbles into sand. Much of this sand is pure enough [for the] to make glass of the finest quality. It is supposed to be, and probably is the equivalent of the Potsdam sandstone of the New York geologists, and is therefore the oldest of the fossil bearing rocks. The fossil remains of animals found in this rock may therefore, be supposed to be, those of the animals first created; and according to the theory of progressive development, from the lowest to the highest forms of living beings;-the theory of the "vestiges of Creation"-we [may] should expect to find here some of the least organized, and lowest forms of animals. But instead of this we find the Lingula, the shell of a mulluscous animal which stands high up in the scale of organized beings, having a heart, and a circulation of blood! So the theory which makes man only an improved monkey falls to the ground.

This oldest sandstone shows itself at intervals throughout the northern portion of the Territory from the Wisconsin river to Lake Superior. It is most fully developed at the place known as the "Pictured Rocks" on that great lake.

16.

I have now gone through with all the rocks of a sedimentary character. They are so called because they are supposed to be sediment deposited from water. Those that remain to be considered, are of very different character. They are called igneous or volcanic rocks from the fact of their having been melted and pushed up, as it were, from the depths of the earth.

The most recent of these rocks in Wisconsin, are those which in popular language go under the general name of "trap rocks". They exists at the Falls of the St. Croix; on the upper Wisconsin; on the shores of Lake Superior, and at various other places in the northern part of the Territory. In some localities they assume a columnar appearance resembling, rudely, the celebrated Giant's Causeway in Ireland. The rich mines of copper on Lake Superior are connected with these rocks, and hence it is of peculiar importance that their character, and localities should be carefully studied. But the country in which the trap abounds has not yet been much explored. The settlements in that region are confined to the immediate valleys of the larger streams, and in the immediate neighborhood of the saw mills;-lumbering being the principal business pursued. Many very interesting and useful facts remain to be discovered, as the country becomes known. A partial survey has been commenced by the United States, but no report has yet been published of the result. When this is completed we may expect many important discoveries to be brought to light.

17.

It only remains to notice those rocks usually called primitive, because they are supposed to be the oldest. These are found in various places in the northern part of the Territory, [between the] north of a line extending from the Falls of Saint Anthony in an easterly direction by the Falls of the St. Croix, Chippewa, [and] Wisconsin and Menomonee rivers. So little is known of the character of these rocks and their localities that I will not attempt to give you a detailed account of them. They are very different from our horizontal strata of limestone in this part of the Territory, and the soil produced by their decomposition, is very different, being usually more sandy & sterile.

A singular and unexpected discovery has recently been made, of the existence of a ridge of primitive rock, associated directly with the limestone rocks of the southern part of the Territory. Several years ago, the late Mr. J.L. Tahyer, informed me that he had discovered what he supposed to be a locality of granite in Dodge county, near the western branch of Rock river. The thing seemed so very improbable, that he scarcely believed it could be so himself, and no farther [notice] attention was given to the subjects at the time. The place has recently been visited, however, by my friend [Mr.] N.F. Hyer Esq. who reports that a remarkable dyke or ridge of these rocks, does actually exist there. In his letter to me concerning it he says

"The specimen accompanying this letter is really a granitic rock, but is chiefly composed of quartz and red gamets.-"

18.

Feldspar, an essential ingredient of true granite is not to be found in it; and the mica is only in a very small proportion. So far as I am able to judge from the specimen, I should think we have here a building material of great value, on account of its hardness and durability. Most of the stone used in the western country for the purposes of building are either limestone or sandstone; neither of which possess any very great degree of durability. Upon opening a new quarry, the workmen are usually obliged to remove great quantities of decayed and rotten stone, before they come to that which is solid: the farther they penetrate into the ledge, the more solid and durable the stone is found to be. This only indicates that the stone is easily decomposed by the action of the weather upon it, and is entirely unfit for structures that are designed to last more than a few years, or at most a century or two. Had the pyramids of Egypt been constructed of such materials we would have been saved all our speculations about their origin, and the purposes for which they were constructed.

Hence we may regard this discovery of granite in Dodge county as of peculiar value to the people of southern Wisconsin. We may now construct effigies and monuments, with the assurance that they will last. It is therefore not only a singular and interesting feature in the geology of Wisconsin, but it is of great practical value to us. I regard the Milwaukee brick and the Dodge county granite as the only building materials we have that are really durable in their nature.