No. 5.] SPENCER — SURFACE GEOLOGY. 271 



the outlets of the lake by these routes (as also those of the upper 

 lakes). Prof Lesley seems to favor the hypothesis of the former 

 outlet of the Ontario basin by the Mohawk and Hudson rivers, 

 but points out that the valley is underlaid by solid rocks at 

 Little Falls (Herkimer County) at au elevation of 350 feet above 

 tide. Therefore the deepest portion of the lake would be 850 

 feet below this barrier in the great valley. In closing the para- 

 graph, the above named distinguished geologist says that if the 

 above route be correct, then the country about Little Falls must 

 have been elevated (query: by the Mohawk uplifts, as items of a 

 more general Hudson river uplifts) more than 900 feet. And 

 this may possibly give us a rude geological date for the elevation 

 of the Catskill -'mountain plateau, sloping westward into Penn- 

 sylvania." 



It is by no means necessary to assume that the local elevation 

 which cut off any outlet to the .sea, by either the St. Lawrence or 

 Mohawk-Hudson rivers, took place during or at the clo.se of the 

 Ice Age ibr the period of the river-valleys just described dates 

 f\ir back in geological time. If the explanations brought forward 

 be wholly correct, then the date of the commencement of the val- 

 leys should be placed after the close of the Palaeozoic time, as the 

 valley of the Susquehanna, and some of the ancient rivers entering 

 the lake basins are partly excavated out of carboniferous rocks, 

 which had been previously elevated. This would agree with the 

 older portions of the Mississippi river. However, the Great 

 River Age did not culminate until the middle Tertiary times, as 

 shown by the tributaries of the ancient Mississippi. 



In the Ice Age the outlets of the lakes were closed by drifts 

 in addition to the agency of local oscillation. Whether the fill- 

 ings of the valleys were produced by glacier-action, by the agency 

 of icebergs, or by that of floating pan-ice, a rational explanation 

 might be given ; but as this depends upon unsettled glacial 

 geology, I will not here delay by entering into discussion. How- 

 ever, there appears to be every evidence of an Inter-glacial epoch, 

 when the greater portion of the present Dundas valley, the 

 Niagara river, by the old buried channel of St. Davids, and 

 many other valleys, everywhere in the lake region, were either 

 re-excavated in the drift, or originally opened ; and that the 

 second closing or filling of these valleys was not accomplished 

 through any glacier action, but principally tlirough the agency 

 of pan-ice and currents. 



