554 THE ICE AGE IN NORTH. AMERICA. 



loam. Even the immediate river-bank, where the lime-rock 

 should be intact, shows that it has been extensively disrupted 

 and its debris, often coarse and water- worn, in pieces from four 

 to ten feet long, is mixed with the coarse bowlders, gravel and 

 the drift, at the height of fifty to seventy-five feet above the 

 water-level, the heterogeneous mass lying on the worn upper 

 surface of the St. Peter sandstone. But above Fort Snelling 

 the upper edge of the lime-rock is* intact all the way to the 

 falls, and shows a fresh-cut section. It is surmounted by a 

 continuous sheet of drift, which rises from the water-level in 

 one bluff coincident with the rock-cut. Its individual strata 

 show that they were cut by the recession of the falls in the 

 same manner as the strata of the rock. They do not conform 

 in their undulations to the outline of the rock, as if the gorge 

 were present when they were formed, as at St. Paul. There 

 is no spreading of loam over these cut edges, except such as 

 has fallen down from above at the time of their removal or 

 subsequent to it. At Fort Snelling, the direction of the Mis- 

 sissippi changes abruptly at a right angle. The change is 

 caused by entering the wide gorge which runs in that direc- 

 tion. This gorge is that in which the Minnesota runs, and is 

 out of proportion with the amount of water which it carries. 

 This valley continues in the same direction, and with the same 

 width, beyond the confluence of the Mississippi, but takes the 

 name of the latter stream. At one mile below the mouth of 

 the Minnesota it is a mile and a half wide. 



These features of greater age, pertaining to the bluffs of 

 the Mississippi below Fort Snelling, are seen in the old rock- 

 bluffs of the river above the mouth of Bassett's Creek as far as 

 to Shingle Creek. The rock there is deeply changed in color, 

 and is hid by the drift, and the bluffs, as left by the more an- 

 cient river, are far apart, the old gorge being three or four 

 times as wide as that between the falls and Fort Snelling. 

 These rock-bluffs, consisting of the same limestone as that 

 which at the falls is below the water, here rise from thirty to 

 forty feet above the river, and are buried under loam, or under 

 drift and loam. This part of the old valley continues south- 

 wardly, by way of Bassett's Creek (below its last turn), across 

 the western suburbs of Minneapolis, through the valleys occu- 



