World-life; or, Comparative geology . a period of 64,842 years. Mr. ThomasBelt,* after a careful examination, assumed the rate ofrecession at .01 foot per annum. But he announced theimportant discovery, if a fact, that the ancient gorge,from the whirlpool to St. Davids, on the Canadian side,now filled with gravel, was excavated in pre-glacial times;and the old gorge apparently extended, also, up nearly tothe present falls. In this view, the only post-glacial workis included between Queenston and the whirlpool, withthe addition of an unknown, but probably small, portionof the gorge above thewhi
World-life; or, Comparative geology . a period of 64,842 years. Mr. ThomasBelt,* after a careful examination, assumed the rate ofrecession at .01 foot per annum. But he announced theimportant discovery, if a fact, that the ancient gorge,from the whirlpool to St. Davids, on the Canadian side,now filled with gravel, was excavated in pre-glacial times;and the old gorge apparently extended, also, up nearly tothe present falls. In this view, the only post-glacial workis included between Queenston and the whirlpool, withthe addition of an unknown, but probably small, portionof the gorge above thewhirlpool. Mr. Belt as-sumes, however, in roundnumbers, that 20,000years express the maxi-mum limit of time sincethe commencement of thenew gorge at own assumption of therate of recession wouldgive for the three miles be-low the whirlpool, 158,000years, which, as Mr. Beltrecognizes, is more thanthe time at our disposalfor the incrusted historyof the earth will accompanying dia-gram will illustrate Fig. 53. Mr. James T. Gardner, Niagara Gorge-New. •Old and ?Thomas Belt, (^uar. Jour, of Science, April, 1875. THE EARTH. 371 Director of the New York State Survey, has given atten-tion to the rate of recession of Niagara Falls, reproducingHennepins narrative and illustration, and the map of thetriangulation of 3 8-42, by Mr. Blackwell.* On the lat-ter he has laid down also the line of the falls as deter-mined by the United States Lake Survey in 1875. f Fromthis comparison is shown the unexpected fact that the HorseShoe Falls have receded, in places, 160 feet during thirty-three years, and that a large island has disappeared whichformerly existed in the midst of the Canadian Rapids. Inspite of some slight inaccuracy resulting from the indepen-dent datum points of the surveys of 1842 and 1875, the errorscannot be so great, as Director Gardner informs me, thatthe assumption of a recession of 100 feet in thirty-threeyears would involve any degree o
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