393

Rock river, opposite La Belle Lake

66 at Jefferson

Hill at west end of Pewaukee Lake

The following altitudes are estimated, from levels taken by Capt. Cram, at the rapids on several rivers, and an allowance made for the descent between them. They are supposed to be nearly correct:

Summit between Lake Winnebago and Plum creek (85.5 above

Lake Winnebago)

245

Marsh at the head of north branch of the Manitowoc river (68

The following list of elevations is made from the Report of Mr. Nicollet, except the last four which were reported by Captain Cram. They were ascertained by means of the barometer, and are probably very nearly correct:

Surface of the Mississippi

At Rock Island, mouth of Rock river (below Lake Michi

Feet

Dividing ridge between Sappah or Black river and the Prairie

la Crosse river, six miles east of the Mississippi,

525

The following table of the latitude north, and longitude west, from Greenwich, of places within this Territory, is given here in this form, as affording greater convenience of reference than if given under the head of the several places. The observations were made by officers of the United States-principally by Mr. Nicollet. That they are not in all cases precisely accurate, is shown by the difference of the observations of different persons at the same places; as at Prairie du Chien (Fort Crawford) and the mouth of the Montreal river:

The reader will not, of course, expect much information relative to the geological character of a country so recently brought into notice, a large part of which is still uninhabited by civilized man; and all that can be attempted is a brief outline. Several geologists have travelled hastily through the country, mostly in small canoes along the principal rivers and lakes, and have published accounts of their necessarily limited and hasty observations. Among them are Mr. Schoolcraft, Mr. Keating (who was attached to Long's expedition), Mr. Featherstonhaugh, United States geologist; and more recently, Mr. James Hall, one of the geologists of the State of New York, I. H. Nicollet, H. King, and J. P. Hodge.

In 1839, a very minute and elaborate geological survey was made, under the authority of Congress, by Dr. D. D. Owen, and Dr. John Locke, of the "mineral region" in this Territory, as well as in Iowa and Illinois; but as their report has never been fully given to the public, the results of this survey are but little known.

The Territory may very naturally be divided into four geological districts, differing very materially from each other in physical character, dependent upon the rocks prevailing in each. They will be demonstrated, 1st, the

Primitive; 2d, the Sandstone; 3d, the Mineral; and 4th, the Limestone Districts.

I. So far as is at present known, all the northern portion of the Territory, extending down the Mississippi nearly to the Falls of St. Anthony, thence across to the Falls of the rivers St. Croix, Black and Wisconsin, and thence to Lake Superior, along the course of the Chocolate river in Michigan, may be considered as PRIMITIVE, or abounding in primitive rocks. They are mostly granite and hornblende rocks, but the other varieties of rocks belonging to this class are also found, as is evinced by the following list of the localities observed by the geologists who have visited this region. The only rock other than primitive in this district, is the "old red sandstone," one of the oldest of the transition rocks. Red-rock Island, in the Lake of the Woods, derives its name from a red GRANITE rock, of which it is composed. Granite is also one of the most common of the boulders scattered over the Territory. Most of the islands in that lake, and Rainy Lake, which is similar to it in general character, consist of MICA SLATE, the vertical layers of which are constantly decaying and falling into the water. TALCOSE ROCK is said to be found on the Mississippi, at the Little Falls; and as this is the only rock in which gold occurs in the United States, it may be important to examine this locality with care. HORNBLENDE ROCK is found at many of the rapids on the Upper Mississippi; and it constitutes that rough, high, broken promontory extending into Lake Superior between the bays of Fond du Lac and Chegoinegan, called the Detour. A large proportion of the boulders contain more or less hornblende in their composition. Some of the rocky islands of the Lake of the Woods, and of Rainy Lake, are composed of SIENITE, which also occasions the falls at the outlet of the latter, where the water falls into the river over a ledge twenty-five feet high. ARGILLITE is found at the "Portage aux Coteau," on the St. Louis river; the sharp edges of