No. 5.] SPENCER — SURFACE GEOLOGY. 269 



sufl&ciently long at the level of the upper part of Seneca valley, 

 to produce beaches at the same level along various portions of 

 the margin of the basin. 



Unless there was a great relative change of continental level, 

 the route just described could not have been the Preglacial outlet 

 of the basin of Lake Ontario, as a considerable portion of the 

 canon of the Susquehanna for several miles below Towanda (738 

 feet above the sea) " has a rocky bottom." Cayuga valley would 

 not afford any better outlet, as its summit is 200 feet higher 

 than that of the valley of Seneca lake, and connects with the 

 Susquehanna by diminished valleys. 



A pot-hole at the inouth of Chesapeake Bay indicates an 

 ancient depth of the Susquehanna River to at least 1170 feet 

 below sea-level. Many of the streams in northern Pennsylvania, 

 now tributaries of the Susquehanna, indicate an original north- 

 ward flow to Seneca lake, 



OsciUations of the Continent In the Lake region. — Until re- 

 cently my investigations bearing on the origin of the great lakes 

 have been mainly based on the hypothesis that the closing of the 

 basins was not occasioned by the elevation of the lake margins, 

 by means of the local elevation of the earth's crust. This hypo- 

 thesis then necessitates the existence of buried channels being- 

 outlets of the lake basins, which, if iheir contained drift were ex- 

 cavated, would restore the Preglacial drainage. My recent ob- 

 servations in New York and elsewhere have failed to obtain any 

 proofs of the existence of such channels. 



Outside of the region of the lakes, in the Red river valley, 

 there are known, at least, two deep bore-holes far apart where the 

 drift extends to a level below that of Lake Winnipeg, and indi- 

 cates that if the drift were removed from the Red-Minnesota 

 valley the drainage of some of the great lakes and rivers of the 

 Canadian North West territories would flow to the Mexican 

 Gulf (as first pointed out by General Warren) without the neces- 

 sity of a local change of level. This fact extended to the lake 

 regions strengthened my opinions as to the correctness of the 

 above hypothesis. 



Whilst the fluviatile origin of Lake Ontario is apparent, yet 

 the failure of demonstrating a drift-filled outlet for the basin 

 (which is 500 feet below the level of the sea) has forced me pro- 

 visionally to accept the hypothesis that the basin was partly closed 

 by oscillations of the region, as strongly set forth in an able letter 

 from Mr. G. K. Gilbert. 



