APPENDIX. 329 



vapor condensed upon these summits, and falling in dews, rains, 

 and snows, being arrested by the impervious subsoil of clay, has 

 concentrated itself in innumerable lakes, of all imaginable forms, 

 from half a mile to thirty miles long. These are connected by a 

 network of rivers, which pour their redundancy into the Missis- 

 sippi, and keep up a circulation over the whole vast area. The 

 sand plains often resting around the shores of these lakes create the 

 impression of bodies of water resting on sand, which is a fallacy. 

 Some of these bodies of water are choked up, or not well drained, 

 and overflow their borders, forming sphagnous tracts. Hence the 

 frequent succession of arid sand plains, impassable muskeegs, and 

 arable areas on the same plateaux. Every system of the latter, of 

 the same altitude, constitutes a plateau. The highest of these is 

 the absolute source of the Mississippi waters. The next descend- 

 ing series forms another plateau, and so on, till the river finally 

 plunges over St. Anthony's Falls. 



In this descending series of plateaux, the Cass, Leech Lake, and 

 Little Lake Winnipec form the third and fourth levels. 



In descending the Mississippi below the Pakagama, the first 

 stratum of rock, which rises through the delta of the river, 

 occurs between the mouth of the Nokasippi and Elm Rivers, 

 below the influx of the Great De Corbeau. This rock, which 

 is greenstone trap, rises conspicuously in the bed of the stream, 

 in a rocky isle seated in the rapid called — I know not with 

 what propriety — the Big Falls, or Grande Chute. The pre- 

 cipitous and angular falls of this striking object decide that 

 the bed of the stream is at this point on the igneous grani- 

 tical and greenstone series. This formation is seen at a few 

 points above the water, until we pass some bold and striking 

 eminences of shining and highly crystalline hornblendic sienite,- 

 which rises in the elevation called by us Peace Rock, on the 

 left bank, near the Osaukis Rapids. This rock lies directly 

 opposite to the principal encampment on the 27th of July, which 

 was on an elevated prairie on the west bank. To this point a 

 delegation of Sioux had ascended on an embassy of peace from 

 Fort Suelling to the Chippewas, having affixed on a pole what 

 the exploring party called a bark letter, the ideas being repre- 

 sented symbolically by a species of picture writing, or hiero- 

 glyphics. In allusion to this embassy, this locality was called the 



