NIAGARA FALLS AND VICINITY 5 1 



glacial period, but that comparatively little erosion was accom- 

 plished. This is farther borne out by minor relief features, such as 

 the benches shown in sections 4, 5 and 6, in the southern wall of 

 the basin, and which probably consist of harder beds which erosion 

 has left standing out in relief. On the theory of glacial erosion, we 

 might expect these to be absent, or at least much less prominent, 

 since ice would hardly show such selective power as is attributable 

 to running water and atmospheric agents. 



With the failures of the theories that an eastward flowing stream 

 or glacial ice produced the Ontario valley, we are forced, with 

 Upham, Russell and others, to look on a westward flowing stream 

 as the most probable agent in the production of this valley. As has 

 before been shown, such a stream would be the normal result of a 

 gradual development of a drainage system on an ancient coastal 

 plain of the type here considered. 



Ancient St Davids gorge. Since the time of Lyell, the old buried 

 channel from the whirlpool to St Davids has played a prominent 

 part in the discussion of the life history of Niagara. For a long 

 time it was considered to be the preglacial channel of Niagara, or its 

 predecessor, the Tonawanda. More recently it has been considered 

 of interglacial age, eroded by an interglacial Niagara, during a tem- 

 porary recession of the ice sheet from this region, and filled with 

 drift during a readvance of the glacier. The most satisfactory inter- 

 pretation of this channel however makes it independent of the 

 Niagara, and considers it one of many preglacial or interglacial 

 channels which were formed by streams flowing over the edge of 

 the escarpment and which increased in length by headward gnawing 

 of their waters. This type of stream we have learned to call obsc- 

 qucnt, its direction of flow being contrary to that of the master 

 stream to which its waters eventually become tributary. An illustra- 

 tion of channel-cutting by streams flowing over the edge of a cliff, 

 may be seen today in the chasm near the Devil's hole, on the Ameri- 

 can side of the gorge below the whirlpool. This gulch was cut by 

 the little stream known as the Bloody run, which during the sum- 

 mer season dries away entirely. 



The St Davids gorge has a width of nearly 2 miles at the edge 

 of the escarpment. As will be seen by a glance at the map, it nar- 



