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novelty in the appearance of the topography, that they employed new 

 names to designate it. Hence, we have the expressions: Coteau des 

 Prairies, Coteau des Bois, Hauteurs des Terres, and roUing, flat, or 

 marshy prairies. 



Of course these names are appUcable only to certain sections of the 

 country, for neither of them would express its general character; and, in 

 fact, the vast region comprised by my map has no prominent feature by 

 which it could be described as a whole, unless it be some geological traits 

 that cannot be made apparent to every one. And I would particularly in- 

 sist that the map, as it appears in its published form, ought not to leave 

 an impression upon whoever consulted it, that the country which it is in- 

 tended to delineate is nothing more than a succession of lakes, marshes, 

 and f-avannahs. There is still sufficient variety in the irregularities of its 

 surface, and the distribution of the watercourses, woodlands, and pai- 

 ries, to bestow interest and value upon its several subdivisions, each of 

 which would require a separate description. But this would be rather 

 long, and made tedious by frequent repetitions. Fortunately, however, 

 the task can be simplified, the repetitions avoided, and much time gained, 

 if, previous to entering directly into the subject, I am allowed to say a 

 few words on that geological feature of the country to which 1 have before 

 alluded. 



The region comprised within my map is covered by a species of de- 

 Erratic de- posite of the kind for a long time known by the name of dilu- 

 po^iies, vlum ; but as this word implies a theoretic idea as regards the 

 accumulation of such deposites, the cause of which is still open to con- 

 troversy, it is now very generally abandoned, and the designation of er- 

 ratic deposites, among others, adopted in its stead. 1 have, therefore, used 

 the latter expression, as comprehending a vast dcposite of sand, gravel, 

 pebbles, and clays, (arranged in zones, and occupying almost always the 

 bottoms.) and masses of rocks transported to a distance from their origi- 

 nal position, usually called erratic blocks. This deposite always occurs 

 between the vegetable soil and the rocky strata of all ages thai 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 Mississippi, 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 deposite 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 contrib- 

 uted 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 

 abou its characteristic features. 



The erratic blocks of this deposite are not generally rounded, but they 

 Erraiic are Still boulders. Those which have the rounded appearance, 

 blocks. niost usual to boulders, among a great many that 1 had an op- 

 portunity 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 arc buried in the soil, and in this way pro- 



