Birth of Lake Ontario. 447 



the crest of the highest ridge, where the beach is broken into 

 a number of ridgelets, having sometimes a vertical range of 

 twenty-five feet or more. 



Thus we see that the Iroquois Beach has been deformed to 

 the extent of 609 feet, between the western end of Lake 

 Ontario and Fine, of which only 78 feet of rise occurs upon 

 the southern side of the present lake, while the great propor- 

 tion of the uplift is found west and northwest of the Adiron- 

 dack Mountains. Upon the northern side of the lake, the 

 eastern equivalent of uplift is more pronounced. At the 

 western end of the lake, the mean maximum uplift is 1/60 feet 

 per mile in a direction of N. 28° E. This rate increases to- 

 wards the northeast. To give a mean rate of rise, at the eastern 

 end of the lake, does not convey a correct idea, for the uplift 

 increases in a progressive ratio. Thus in the region of Oneida 

 Lake, the uplift is 3 5 feet per mile, while in the region of 

 Watertown it amounts to 5 feet per mile ; and farther north- 

 eastward the deformation reaches 6 feet per mile, in the direc- 

 tion of 1ST. 60° E. This seems an extraordinary amount of 

 measurable terrestrial movement, but the records are inscribed 

 in the beach. It is not yet known where this upward move- 

 ment ceases. 



Upon the Erie beaches, outside of the Ontario basin, Mr. 

 Gilbert found a considerable amount of warping recorded at. 

 Crittenden, ]ST. Y., over the horizon at the western end of the 

 same lake. I have traced the Erie beaches around to the 

 southeastern side of Lake Michigan. Combining our results, I 

 find the measured uplift between the two regions amounts 

 to 324 feet. But the beach, where last observed near Lake 

 Michigan, is 45 feet above its surface. Indeed, it is there diffi- 

 cult to trace, owing to the druny character of the sandy country. 

 By the assistance of other beaches found in that region, the 

 conclusion is readily arrived at that the shore-line under con- 

 sideration must pass from 40 to 60 feet beneath the waters of 

 the lake at Chicago. It is then evident that the terrestrial 

 uplift, between Chicago and Crittenden, amounts to not less 

 than 410 feet. Crittenden is nearly on the line of strike of the 

 Iroquois beach (S. 62° E.), at its lowest point, with Hamilton. 

 The Erie beaches, eastward of the ISTiagara River, were de- 

 formed to the extent of 0*4 feet per mile before the Iroquois 

 episode, the remainder of their uplift having been synchronous 

 with that in the Ontario basin. But the pre-Iroquois differ- 

 ential uplift of the beaches farther west is reduced to almost 

 zero, for the beaches south and west of Lake Erie have suffered 

 very little deformation. Consequently a sufficient amount of 

 deformation of the beaches has been measured to allow for inac- 

 curacies when we take the elevation of the Iroquois Beach above 



/ 



