9 [ 237 ] 



tected ; their angles and corners show but little erosion. On the other 

 hand, wherever there is a deposite of pebbles, its oris^in may be easily traced 

 to local causes that have acted long after the arrival of the erratic deposite 

 now under consideration. 



It is difficult to determine the direction whence the materials of the erratic 

 deposiie 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 tlie great lakes, on the flanks of valleys, and where 

 traces of recent floods are apparent, the erratic blocks are in great abund- 

 ance. 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 oryctoguostic distinctions, are — granitic sienite, resembling the Egyp- 

 tian 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 carnelians. These last are carried off by 

 the streams, and scattered in great numbers over the shores of the Missis- 

 sippi 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 silicious. It is this sand which constitutes the predomi- 

 nant ingiedient in the soils of the whole region embraced in the map, mod- 

 ified, according to localities, by the presence of carbonate of lime, mag- 

 nesia, oxide of iron, &,c. 



I need add nothing more of a general nature as regards the erratic de- 

 posite, having introduced an account of it in this place more with the view 

 of its bearing upon the agricultural condition of the country, than to discuss 

 its importance as a geological phenomenon. It may be concluded, from 

 what 1 have said of it, that there is no region laid down on the map that is 

 to be considered as desert. The country is still unknown ; there are soli- 

 itic/cs — that is, uninhabited, but habitable regions. 



The basin of the Upper Mississippi is separated, in a great part of its ex- 

 Cotean des tent from that of the Missouri, by an elevated plain ; the appear- 

 Prairies. ance of which, seen from the valley of the St. Peter's, or that of 

 the riviere Jacques, loo?ning as it were a distant shore, has suggested for it 

 the name of Coteau des Prairies. Its more appropriate designation would 

 be that of plateau, which means something more than is conveyed to the 

 mind by the expression, a plain. 



Its northern extremity is in latitude 46°, extending to 43°; after which 

 it loses its distinctive elevation above the surrounding plains, and passes 

 into rolling prairies. Its length is about two hundred miles, and its 

 general direction NNW. and SSE. Its northern termination, (called 

 Te'e da Coteau, in consequence of its peculiar configuration) is not more 

 than 15 to 20 miles across ; its elevation above the level of the Big Stone 

 lake is S90 feet, and above the ocean 1,916 feet. Starting from this ex- 

 tremity, (that is, the head of the Coteau,) the surface of the plateau is undu- 

 lating, forming many dividing ridges which separate the waters flowing 

 into the St. Peters and the Mississippi from those of the Missouri. 



