«rant] GEOLOGY OF MINNESOTA. 303 



is about tea thousand, and they are scattered over nearly the entire 

 surface of the State, but the larger proportion are confined to the 

 inorainic areas. These lakes are of all sizes, from small ponds to 

 bodies of water 12 miles (1!) km.) or more in diameter. Their shores 

 are mostly of drift, and rarely does the underlying rock appear any- 

 where in their basins. Tin's is not true of those lakes in the district 

 between Lake- Superior and the Canadian boundary, which are for the 

 most part rock bound. 



There are three drainage systems. The most important is that whose 

 waters find their way into the. Gulf of Mexico through the Mississippi, 

 whose largest tributary in the State is the Minnesota river. This basin 

 includes fully two-thirds of the area of the State; the whole of the 

 southern half, the northern-central and the central-eastern part of the 

 State belong to it. The next largest is the Hudson Bay system, includ- 

 ing the Red River of the North, which drains the northwestern portion, 

 and the Rainy river which drains a small strip along the northern edge 

 of the State. The third system is that of the Gulf of St. Lawrence; 

 this is by far the smallest of the three systems and includes only the 

 streams in the immediate neighborhood of Lake Superior. 



Flora.-' — The most important and conspicuous contrast presented 

 by the vegetation covering different parts of Minnesota is its division 

 into forest and prairie. Forest covers the northeastern two-thirds of 

 the State approximately, while about one third, lying at the south and 

 southwest and reaching in the Red River valley to the international 

 boundary, is prairie. The line dividing these areas has an almost 

 wholly timbered region on its northeastern sideand on its southwestern 

 side a region that is chiefly grass land, without trees or shrubs except Lng 

 in narrow belts along the larger streams and occasionally groves beside 

 lakes. Iu the northern half of t he State the timber consists largely of 

 conifers, from which large amounts of lumber are annually taken. The 

 deciduous forest exists for the greater part in the southern half of the 

 State, and is composed chiefly of various species of oak. elm. linden, 

 poplar, maple, and ash. 



The geological oolumn.—ln the State of Minnesota there are. to be 

 seen rocks from the fundamental complex of gneiss and schist (Archean) 

 up to those which are being funned at the present day. There are. 

 however, several wide breaks iu the geological column where formations 

 of great importance are entirely lacking. In the Paleozoic, Carbonif- 

 erous and Permian are without representatives. In the BfeSOZoic, the 

 Friassic and Jurassic are completely wanting, the only Mesozoic rocks 

 that are known being a few isolated areas of Cretaceous strata, very 

 limited in extent, The Tertiary is also entirely lacking. 



