892 N. H. WINCHELL ON THE EECESSION 



only extending through an interval of forty years, requires a 

 period of time between eleven and twelve thousand years *. 



III. The Recession of the Falls of St. Anthony. 



Fortunately the recession of the Falls of St. Anthony must have 

 been very uniform. The rocks are horizontal and of unvarying 

 composition. A white friable sandstone, over one hundred feet 

 thick, called the St.-Peter sandstone, underlies a more enduring 

 limestone, known as the Lower Trenton limestone. It is this con- 

 junction of formations of different durability, the harder overlying 

 the softer, that gives origin to the Falls. The Lower Trenton is 

 about thirty feet thick, and includes some layers of green shale. 



It is not possible to calculate the time required for the recession 

 of the Falls from Fort Snelling by relying on the known recession 

 since the settlement of the region, though they have gone back 

 about five hundred feet. This extraordinary rate has been caused 

 by artificial means, chiefly by the construction of saw-mills and 

 dams, diverting thereby the current or concentrating it on certain 

 points, and by the passage of logs over the Falls. We must have 

 recourse to historical data. Fortunately we have records of the 

 appearance of the Falls at different times, by which we can fix their 

 position. They were discovered by Father Louis Hennepin, who 

 saw them first in July 1680, in returning from his captivity among 

 the Dakotas. He gives the following brief description, as translated 

 from the French of the Amsterdam edition of his works (1704, 

 chap. 44, p. 319) : — "In ascending this river ten or twelve leagues, 

 navigation is interrupted by a fall, which we named in honour of 

 St. Anthony of Padua, whom we had chosen as patron of our enter- 

 prises. This fall is fifty or sixty feet in height, and has an island 

 of rock in the form of a pyramid in the middle of the chute." The 

 ' Historical Collections of Louisiana,' part iv., contain a translation 

 of Hennepin's narration, in which he gives " 40 or 50 " feet as the 

 height of the Fall. 



Jonathan Carver, a captain of provincial troops in the employ of 

 Great Britain, a native of Connecticut, visited the Falls of St. An- 

 thony during his extensive travels in the North-west in 1766. In 

 the London edition of his Journal, 1778, p. 69, Carver thus describes 

 them : — " This amazing body of waters, which are above 250 yards 

 over, form a most pleasing cataract ; they fall perpendicularly about 

 30 feet, and the rapids below, in the space of 300 yards more, render 



the descent considerably greater In the middle of 



the Falls stands a small island, about 40 feet broad and somewhat 

 longer, on which grew a few ragged hemlock and spruce trees ; and 

 about halfway between this island and the eastern shore is a rock 

 lying at the very edge of the fall in an oblique position, that ap- 

 peared to be about 4 or 6 feet broad, and 30 or 40 long. . . . 



* ' Travels in North America.' Lyell, it is true, does not adopt that datum, 

 but arbitrarily divides it by three, getting 35,000 years for the time needed for 

 the above recession. 



