44 F. W. SARDESON SAINT ANTHONY FALLS 



transverse to the right wall of the gorge. Its crest is 30 paces long, meas- 

 ured from the bank above it to the cliff by which it is now cut off. Up- 

 stream from this remnant of the falls formerly extended a sloping trian- 

 gular area of the upper rapids. It rose over 15 feet in the 120 paces from 

 the top of the falls back to the point where it was cut off by the con- 

 vergence of the bank above and the cliff below it. Formerly many small 

 river shells were found under the limestone shingle, there being a foot of 

 such debris between the soil and the limestone floor, so that these as well 

 as the slope and position of the terrace proved it to have once been the 

 river bed above the falls. The descent of the rapids, 15 feet in 120 

 paces, extended from the top of the i^pper limestone to its base. 



The crest of the fall rested on the top of the lower limestone. The 

 scarp of the fall is now covered in part by the quarry dump, but it was 

 formerly regular, presenting a low cliff bordered by a talus slope, in all 

 20 feet high — that is, reaching from the top to the bottom of the lower 

 limestone. Originally this appears to have been a vertical fall of 20 feet. 

 From the foot of that scarp a steep slope, covered by limestone blocks 

 and debris on Saint Peter sandstone, runs with a gradient of 1 in 5 for 

 100 feet. It changes then to a gradient of 1 in 10, decreasing gradually 

 to 1 in 100 ; so that the bed of the river at 100 paces from the fall was 75 

 feet below the top of the upper limestone — that is, upper rapids — and 60 

 feet below the crest of the falls. The heights here are: upper rapids, 15 

 feet ; fall and cataract, 40 feet ; lower rapids, 20 feet. 



The terrace below the fallscarp consists of limestone blocks 1 foot to 10 

 feet in diameter and boulders, filling over the very unevenly eroded sur- 

 face of Saint Peter sandstone from 5 to 15 feet deep. The terrace is 50 

 to 75 feet wide now and 40 to 20 feet above the river. At 350 feet from 

 the fallscarp the terrace has been disturbed by the building of Lake Street 

 bridge, but remains intact close beyond that obstacle. There it is 20 feet 

 above the present river, has nearly as little gradient as the river, and ex- 

 tends 60 paces wide for 400 paces. Another part of the same is seen a 

 little farther along, beyond a 10-foot lower terrace which suddenly widens 

 back to the foot of the bluff here, after it has paralleled the main terrace 

 in a narrow strip for a long distance. 



The falls at this stage cut the gorge here originally 30 or more feet 

 deeper than it did at and below Minnehaha. ( Compare figures 2 and 3, 

 plate 2.) 



Other Terraces 



In the last 3 miles up to the present Saint Anthony falls each turn in 

 the river's gorge preserves some record in the form of terraces and scarps 



