RECESSION OF THE PALLS OF ST. ANTHONY. 



309 



bluffs. This stained condition also pervades the rock at the mouth of 

 Bassetts creek and at the quarries in the ancient river bluffs near the 

 month of Shingle creek, OD both sides of the river. (Both of these 

 places are above the Falls.) Another notable difference between the 

 bluffs above Fort Snelling and those below consists in the absence of 

 caves and subterranean streams entering the river above Fort Snelling. 

 Although the Trenton limestone exists in fall force about St. Paul, in 

 the bluffs cast and north of the city, yet it has been cut through by 

 some means prior to the drift so as to allow the entrance and exit of 

 streams of water, at levels below its horizon, through the sandstone. 

 None such are found above Fort Snelling, the surface drainage being 

 shed by the limestone and precipitated over the brink of the gorge in 

 Several beautiful cascades. When such streams enter the river below 

 Fort Snelling they either enter some subterranean passage and appear 

 at the mouths of caverns in the sandstone, or as springs in the drift 

 along the talus, or they find an ancient ravine down which they plunge 

 by a series of rapids over bonldcrs to the river level, rarely striking 

 either the limestone or the underlying sandstone. Again, the rock 



zr T X r , - i - ■ I T I T r 



i i i i T 1 V*f to ^ , ~r i i i ' ! -t 



Fig. 18.— Section aorosa the Mississippi River below Fori Snelling. 



bluffs at St. Paul and everywhere below Fort Snelling are buried under 

 the drift sheet. Their angles are sometimes seen jutting out from some 

 wind beaten corner, but nearly everywhere they are smoothed over by 

 a mantle of diil't and 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 1 to 10 

 feet long, is mixed with coarse bonldcrs. gravel and drift at the height 

 of 50 to To feet (15 to 23 m.) above the water level, the heterogeneous 

 mass lying OL the water- worn surface of the St. Peter sandstone.* But 

 above Fort Snelling the upper edge of the limestone 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 as a direct continuation of the bluff 

 formed by the underlying rock. The individual strata of the drift show 



' A g • example of this is Been along the Chicago, Milwaukee and St. Paul Rail- 

 road tracks just wee! of the Union station at St. Paul. 



