298 DESCRIPTION OF THE COUNTRY BETWEEN 



drift banks, from twelve to fifteen feet high, and covered with scrub pine, approach 

 the river on the west side, and continue for nine or ten miles. From this point to 

 the outlet of Sandy Lake, the river bottoms are, in all respects, like those just de- 

 scribed. 



We entered the outlet of Sandy Lake on the morning of the 22d of June, at half- 

 past eight o'clock, and pitched our tents on the island nearest to, and immediately 

 opposite, the Indian village. 



Between Crow Wing and Sandy Lake, there is no rock visible in place on the Mis- 

 sissippi. The sections exposed by the river, throughout the whole distance, present 

 deposits of clays, sands, pebbles, boulders, and loam ; varying in thickness from ten 

 to one hundred and twenty feet. Such deposits are usually described as a part of 

 the drift formation, although it is evident, to my mind, that they were deposited 

 under very different circumstances from those which operated during the great 

 " erratic" period. 



In some places the drift-hills are conical, or, rather, domelike ; but, most gene- 

 rally, the elevations are in the shape of narrow, oblong ridges, with gently undu- 

 lating valleys between them, and, occasionally, wet meadows, bogs, and small ponds. 



The lowest member of this formation exposed on the Mississippi, is a stiff", tena- 

 cious, blue clay, containing numerous small siliceous pebbles and gravel-stones, 

 derived principally from calcareous rocks. It effervesces strongly with acids. The 

 upper part of this clay is, in many places, red, and the numerous small springs 

 which discharge at its junction with the sand-beds above, are highly charged with 

 iron. The thickness of the clay varies from four to thirteen feet, though its total 

 thickness could not be determined with accuracy, as the beds are only elevated 

 above the water for short distances, and at long intervals, sufficiently high to show 

 the base upon which they rest, which is a boulder deposit, embedded in sand and 

 gravel. At the points where these boulders are elevated, they form slight rapids, 

 varying from fifty yards to half a mile in length. The clay-beds are often thinly 

 laminated, and, at some exposures, the laminte are wrinkled. They conform in 

 their dip to the general undulations of the country. In some places, the upper part 

 of the clay-beds have thin seams of sand running through them. 



The clays are overlaid by a deposit of coarse sand, distinctly bedded, and con- 

 sisting principally of quartz grains, mostly rounded, but many of them angular. 

 Quite a large percentage of the sand appears to have been derived from trappous 

 rocks, and is in the form of irregularly-rounded greenish grains, generally smaller 

 than the siliceous particles. 



The lower sand-beds are generally yellow, sometimes of a dark reddish-brown 

 colour, and frequently contain crusts cemented by oxide of iron. The upper ones 

 are lighter-coloured, and, near the surface, present a pale yellow appearance. Not 

 unfrequently, the upper beds contain stripes of dark yellow and red sand, and occa- 

 sionally exhibit lines of oblique lamination. 



Above the beds just described is a bed of sand, from three to six feet thick, filled 

 with rounded pebbles and small boulders, derived from granitic and metamorphic 

 rocks ; and overlying the whole is a deposit, of variable thickness, of sand and loam, 

 and soil. 



