The Parallel Drift-Hills of WeMern Netv York. 259 



the southern, southwestern and western slopes of the Canadian 

 highhmds. To quote his own words : " The effect of this glacier 

 ujoon Lake Erie and Lake Ontario, would be to broaden their 

 basins by impinging against and grinding away, with incon- 

 ceivable power, their southern margins. To the action of this 

 agent we must ascribe the peculiar outline of the profile sections 

 drawn from the Laurentian hills across the basin of Lake On- 

 tario to the Alleghanies, and across Lake Erie to the highlands 

 of Ohio, viz., a long, gradual slope from the north to the bottom 

 of the depression, and then an abrupt ascent over the massive 

 and immovable obstacle against which the ice was banked, until 

 by a vis a tergo, it overtopped the barrier. In New York, that 

 barrier Avas a shoulder of the Alleghanies, too high and too 

 rugged to be buried under a continuous ice-sheet; but its whole 

 front was worn away for a hundred miles or more, and it was 

 deeply creased where we now see the peculiarly elongated lakes 

 of New York, and cut through, in certain gaps, to the valley of 

 the Delaware. In Ohio,' the erosion was easier, and carried fur- 

 ther south. The barrier was also lower, and was finally over- 

 topped by one great lobe of ice, which flowed on to the south 

 and west until its edge reached the Ohio River. * * * 

 AVith the amelioration of the climate, the wide-spread ice- 

 sheets of the pei'iod of intense cold became again Jocal glaciers, 

 whicli completed the already begun work of cutting out the 

 lake basins. At first, the glacier which had before flowed over 

 the water-shed in Ohio, was so far reduced as to be unable to 

 overtop its summit, but deflected by it, it flowed along its base, 

 spending its energies in cutting the shalloAv basin in which Lake 

 Erie 2iow lies. 



"A further elevation of temperature curtailed the glacier still 

 more, and Lake Erie became a water-basin, while local glaciers, 

 left from the ice-sheet, excavated the basins of Lake Michigan, 

 Lake Huron and Lake Ontaiio. The latter lake was apparently 

 formed by the same glacier that made the Erie basin, but when 

 much abbreviated. It flowed from the Laurentian hills and the 

 north slope of the Adirondacks, and was deflected by the high- 

 lands south of the lake-basin, so that its motion was nearly 

 westward." * 



* Geological Survey of Ohio, Vol H, p. 78. 



