100 LAKES OF NORTH AMEKICA. 



charged in some instances with large boulders of crystalline rock, — and as 

 sheets of yellow sand, known as "delta sands," which rest on the clay, and 

 are especially abundant where the mouths of ancient streams were located. 

 Al)0ut the shores of Lake Superior and frequently extending many miles 

 inland, there are ancient clay deposits of a })ink color, that were accumu- 

 lated when the basin contained a much laro-er sheet of water than at 

 present. 



The beaches about the borders of the Laurentian lakes were originally 

 horizontal, but as has been shown especially by Gilbert and Spencer, they 

 are in many cases no longer in their original position. Changes in the 

 elevation of the land have occurred and the beaches have been carried up 

 or down with it. 



The amount of change in level shoAvn by the warping of the beaches 

 about Lake Ontario is considerable, and illustrates the character of the 

 slow upheavings and subsidences known to be in progress over wide areas 

 of the earth's surface. It is stated by Gilbert^ that " the old gravel spit 

 near Toronto, belonging to what is known as the Davenport ridge, is forty 

 feet higher than the contemporaneous gravel spit on which Lewiston is 

 built ; at Belleville, Ontario, the old shore is 200 feet higher than at 

 Rochester ; at Watertown, N. Y., 300 feet higher than at Syracuse ; and 

 the lowest point in Hamilton, Ontario, at the head of the lake, is 325 feet 

 lower than the highest point near Watertown. From these and other 

 measurements shown on Plate 18, we learn that the Ontario basin with 

 its new attitude inclines more to the south and west than with the old 

 attitudes." This general tilting has thrown the waters of Lake Ontario 

 westward and flooded small tributary valleys so as to drown them and 

 make miniature fiords. 



Movements in the earth's crust were also in progress during the long 

 period in which the ancient lakes of the Laurentian basin Avere making 

 their various records, as is shown by the fact that the abandoned beaches 

 do not all lie in planes parallel with each other. 



The hio"hest of the ancient beach lines about the north shore of Lake 

 Superior, has an elevation of about 600 feet above the present lake, as 

 has been determined by A. C. Lawson.^ The beaches at lower levels are 



1 "The history of Niagara river," in Sixth Annual Eeport of the Commissioners of the 

 State Eeservation at Niagara, Albany, N. Y., 1890, p. 69. Reprinted in Ann. Rep. Smith- 

 sonian Institution, 1890, pp. 231-257. 



- "Sketch of the Coastal Topography of the North Side of Lake Superior," in 20th Ann. 

 Rep., Minnesota, Geol. and Nat. Hist. Surv., pp. 181-289. 



