34 



depth of the Eddy basin are almost identical with the 

 average dimensions of the Upper Great gorge between the 

 railroad bridges and the Park bridge. The reef which 

 shuts it off from the whirlpool, coupled with these charac- 

 teristics of depth and width, compel the conclusion that 

 the Eddy basin was made by a vertical cataract, like the 

 present falls and with substantially identical volume. 

 The deep hole of the eddy is behind the reef which separa- 

 tes it from the whirlpool, and there is no way to account 

 for it, except by the vertical plunge of a great cataract 

 which somehow suffered a slight interruption that allowed 

 the reef to remain — either such an interruption or some- 

 thing equivalent to it. 



It seems impossible to explain the depth of the Eddy 

 basin, its separation from the whirlpool by the upper reef 

 and the sudden shallowing and contraction at the mouth 

 of the gorge of the Whirlpool rapids, on the theory that 

 the buried gorge, the Eddy basin and the gorge of the 

 Whirpool rapids were made by a pre-glacial small stream 

 and afterwards weathered out to their present dimensions. 

 The assembled characters in this part of the gorge seem to 

 show clearly that the St. David gorge was made by an 

 inter-glacial Niagara which suddenly ceased at the south 

 side of the Whirlpool basin. But a much smaller stream 

 probably remained and cut a narrow, shallow gorge reaching 

 ioo to 200 yards (90 to 183 m) south from the whirl- 

 pool. When the inter-glacial cataract stopped, the ledge 

 of Lockport limestone which formed the crest of the falls 

 at that time, overhung the south edge of the whirlpool 

 and projected somewhat to the north of the ledges of 

 Whirlpool sandstone which form the present reef. Then 

 after the inter-glacial cataract had ceased, the overhanging 

 ledges fell away and normal cliff recession due to weathering 

 drove the cliff line still farther back, until a relatively 

 stable talus slope was produced. When this condition 

 had been reached a talus slope probably 200 or 300 feet 

 (60 to 90 m.) in width separated the top of the cliff 

 from the reef, that is to say, the top of the cliff, measured 

 on a horizontal plane, was that far south of the reef. 

 Then came the last ice sheet, completely filling the old 

 gorge. When the modern great cataract had gnawed 

 back to the whirlpool and cleared out the filling of drift, 

 it resumed the work of gorge making by a vertical fall at 

 the south side of the whirlpool; not however just where 



