GLACIAL LAKES 



327 



It is interesting to follow this ancient waterway and to discover 

 that, like our normal, present-day streams, it was held up in narrows 

 wherever outcroppings of harder rock had constricted its channel 

 (Fig. 355). The upper end of the Warren River valley is now 



FIG. 355. Narrows of the Warren River below Big Stone Lake, where it passed 

 between jaws of hard granite and gneiss (after Upham). 



occupied by the long and relatively narrow Lakes Traverse and 

 Big Stone, each the result of blocking by delta deposits where a 

 tributary stream has emerged into the valley, but this gigantic 

 channel continues down to and beyond Minneapolis, occupied as 

 far as Fort Snelling by the 

 Minnesota River a mere 

 pygmy compared to its prede- 

 cessor. To the earnest student 

 of glacial geology there can be 

 few sights more impressive than 

 are obtained by standing at 

 Fort Snelling, just above the 

 confluence of the Minnesota 

 and the Mississippi rivers, and 

 surveying first the steep and 

 narrow' valley of the Missis- 

 sippi above the" junction, a 



Stream fitted to its valley for FIG. 356. Map of the valley of the Warren 

 the Simple reason that it has River in the vicinity of Minneapolis, with 



carved it, and then gazing 

 up and down that broad valley 

 in which the great Warren River once flowed majestically to the 

 sea, now the bed of the Minnesota above the Fort and of the Mis- 

 sissippi below it (Fig. 356). 



