APPENDIX.

(A.)

GEOLOGY.

THE country under consideration is of the secondary formation, consisting of the mountain limestone group, and principally, in some parts almost exclusively, of the cliff limestone. It bears marks too distinct to be overlooked, of having been once submerged. The shape and peculiar smoothness of the surface at once gives this idea, which is confirmed on inspection, by finding among the superior strata near the surface, stone composed wholly of fossil marine shells. The uniform slope of the land, also, is another evidence of the same fact. This feature has been mentioned in describing the physical geography. It is about as regular from the Gulf to St. Peter's, as the bed of the sea upon one of our sand beaches, and in the whole distance of more than 1000 miles, does not much exceed a rise of 1000 feet, or one foot to a mile. At the sources of the Missisippi and St. Peter's, we reach the height of land between the Gulf and Hudson's Bay, the waters of Red River, which run into the last, starting almost in contact with the two others. Indeed the passage can be made in boats at seasons of high water, from St. Peter's to Red River. It may be therefore regarded as a certain fact,

that formerly the sea covered this whole valley, from the Gulf to Hudson's Bay, dividing North America into two con tinents, of one of which the Alleghany, of the other the Rocky mountain range formed the nuclei. This would seem to be at a very remote period, as there are indications that it has been inhabited at an antediluvian period. Pieces of pottery have been found in different places, more than fifty feet below the surface, in digging wells: and this position can hardly be accounted for, without supposing a great disturbance of the upper strata of the earth, and also a considerable lapse of time. There is a very abundant deposit of coal in several portions of the valley: beside the large Illinois coal field: generally regarded as evidence of an antediluvian vegetation. According to Mr. Guion, there are large beds of coal on the Des Moines. The erratic deposits are found upon the surface upon very distant points in this region. They are mentioned by Nicollet, upon the Tchansansan and Tchankasndata, as well as high upon the St. Peter's, and the author has observed them upon the Wabesipinicon. Mr. Schoolcraft says the rock on the southern shore of Lake Superior consists of granite, slate, and sand

stone.

The country bordering on the Missisippi, within the inhabited portions of Iowa, and below, is chiefly a mountain limestone. In some localities, as already mentioned, are strata of fossil cretaceous formation, composed mostly or wholly of shell. At the top of the bluff at Burlington, at about 150 or 200 feet above the mark of high water at the usual stage of the river, covered only with a thin layer of chert and vegetable mould of a few inches, is an encrinitic limestone which may, from appearance, be altogether of this shell. And, at Iowa City, the same shell composes a very soft, fine-grained marble of a dingy-white color, which re

ceives a fine polish, and is a highly ornamental and valuable. stone. There is also a soft, black, variegated marble, like the Egyptian, and some other marbles in the southern portion of Iowa, between the Des Moines and Iowa. In some parts of this district bituminous coal has been found, and on the east side of the Missisippi is an extensive bed. Further north, about the Wabesipinicon, is a region of iron, then the great bed of galena or sulphate of lead, and in the farther north the copper district. This is probably the richest mineral region in the world; and to the geologist and mineralogist, an extensive and profitable field of research. The banks of the Missisippi contain great quantities of the precious stones, which are washed out by rains and carried down by the stream. In some places, within four or five years, the writer has found some very beautiful agates and cornelians in the streets of the towns; and, in a stroll of an hour on the shore, has loaded his pockets with them.

There are several very accurate and complete descriptions of the geology of this country. And, instead of attempting to give my own account of it, I shall embody in this part of my work the published account of Long, Owen, and Nicollet, &c., which, together, include the greater part of the country which is the subject of this volune. My own observation of the country, geologically, being very cursory and partial, and the survey of these gentlemen, all scientific men, furnishing a very satisfactory description of the country in this respect I transcribe their observations in extenso. Mr. Nicollet's observations extended over a large portion of this region, and his remarks below give us the result in several different localities. He says:

"The region comprised within my map is covered by a species of deposite of the kind for a long time known by the name of diluvium; but, as this word implies a theoretic idea

as regards the accumulation of such deposits, the cause of which is still open to controversy, it is now very generally abandoned, and the designation of erratic deposits, among others, adopted in its stead. I have, therefore, used the latter expression, as comprehending a vast deposit of sand, gravel, pebbles, clay (arranged in zones, and occupying almost always the bottoms), and masses of rocks transported to a distance from their original position, usually called erratic blocks. This deposit always occurs between the vegetable soil and the rocky strata of all ages that constitute the geological basis of each section of country. To the north and to the south of the western portion of Lake Superior, as far as the upper half of St. Peter's River, it overlies primary rocks; south of the St. Peter's, to the west and east of the Missisippi, it covers silurian rocks; whilst, on the Upper Missouri, it rests upon a cretaceous formation, everywhere mixing itself with the detritus of the rocks in place. The thickness of this deposit is very variable; sometimes only quite superficial, and, when of a more important character, from 150 to 160 feet in depth. It is met with, indifferently, with its erratic fragments, on the summits of hills, on the upland plateaux, over the plains, and in the valleys. It has contributed towards levelling the original irregularities of the soil, by filling up hollows; or varied them, by transporting over the country new materials; whilst the subsequent action of water and weather has further brought about its characteristic features.

"The erratic blocks of this deposit are not generally rounded, but they are still boulders. Those which have the rounded appearance, most usual to boulders, among a great many that I had an opportunity of examining, owe it to their exposure to the atmospheric agents which have worn them down. This is made evident by examining those portions of

them which are buried in the soil, and, in this way, protected; their angles and corners show but little erosion. On the other hand, wherever there is a deposit of pebbles, its origin may be easily traced to local causes that have acted long after the arrival of the erratic deposit now under consideration.

"It is difficult to determine the direction whence the materials of the erratic deposit came. The presumption is, judging from the nature of the erratic blocks-the analogues of which are found in higher latitudes-that they were brought from the north to the south.

"On the borders of the great lakes, on the flanks of valleys, and where traces of recent floods are apparent, the erratic blocks are in great abundance. Their size varies from a few inches to a few cubic feet; yet this seems to bear no relation to the distance whence they are supposed to have come. On

the

contrary, it appears that the largest are often found in the highest spots, and at a greater distance from their origin. I did not find them more abundant on the northern slopes of hills than on the southern. Their oryctognostic distinctions are-granitic sienite, resembling the Egyptian red granite; a true sienite, with white feldspar; a granite, with a large proportion of feldspar; gneiss, amphibolite, red jasper, quartz pebbles, and a great variety of agates and cornelians. These last are carried off by the streams, and scattered in great numbers over the shores of the Missisippi and Missouri; but they have no value, and are collected by travellers merely as reminiscences. The sand and gravel are composed of the small fragments of all these rocks; the sand, though varying according to places, being principally siliceous. It is this sand which constitutes the predominant ingredient in the soils of the whole region embraced in the map, modified according