116 AREA AND DRAINAGE BASIN OF LAKE SUPERIOR 



point it reaches 900 or 1,000 feet and continues at this elevation 

 to the mountains of northeast Minnesota with so slight fall in 

 either direction that it forms a distinct area of independent lakes, 

 generally small in size, but extremel}' numerous, both in north- 

 ern Wisconsin and northern Minnesota. The separation of the 

 waters of the St I^ouis and the Mississippi where they come 

 closest together is but a few feet. The highest knowai point of 

 the watershed is in the Mesabi mountains in northeastern Min- 

 nesota, where it reaches 1,500 feet above the lake, and isolated 

 points are higher. To the north of the lake the Avatershed is 

 more distant from the lake and not so well known. The topo- 

 graphic features on the south side are low-rolling and well 

 rounded. On the northw^est they are sharper, but still preserve 

 the ordinary mountain form, though sharply serrated. This is 

 especially true of the regular indentations of the " Sawtooth 

 mountains," which follow the northwest shore of the lake and 

 in some places form the watershed. As soon as the Canadian 

 border is passed in the west, the escarpment structure becomes 

 marked^that is, an elevated plateau, relatively flat. Through 

 this the streams have cut down 500 or even 1,000 feet, forming 

 a broad, level valley or narrow ravine, but leaving generally 

 nearly vertical walls. This structure is very characteristic of 

 the Thunder bay region and extends eastward to the Nipigon 

 valley, but farther eastward it appears to run out, until to the 

 east of Lake Superior the basin is similar in topography and 

 vegetation to that about the river St Mary. The drainage area 

 on the south shore is narrow, often not more than 20 miles wide, 

 and seldom more than twice that. The tributaries to the lake 

 are here very numerous but small. There are about fourscore 

 that are 20 miles or more long, but few^ of them exceed 50 

 miles. They usually descend rapidly from their source to the 

 lake. In some cases, as in that of the streams at the Pictured 

 Rocks, they have a considerable fall at or near the shore, and 

 the streams that enter at the same level as the lake are usually 

 barred by the combined action of their sediment and the waves. 

 The longest stream on the south shore is the Ontonagon, w'hich 

 enters at Ontonagon, and has a length of 100 miles, with a basin 

 of 250 square miles. 



At the extreme western angle of the lake enters the St Louis 

 river, considered the mother-stream of the lake and the source 

 of the St Lawrence. It is 200 miles long and has a basin con- 

 taining 4,370 square miles. The basin adjoins the remarkable 



