OCTOBEB 16, 1908] 



SCIENCE 



533 



is truly an astonishing relation for a tribu- 

 tary of a river occupying the Ontario Valley. 

 The differences in elevation between the rock 

 bottom of the Canaseraga Valley (modern 

 Grenesee Valley) at Mount Morris, forty miles 

 south of Lake Ontario, and the surface of 

 Lake Ontario, is 136 feet; the rock bottom at 

 Mount Morris is 712 feet above the valley 

 bottom of Lake Ontario opposite the mouth of 

 the modem Genesee, and 874 feet above the 

 deepest part of Lake Ontario, seventy miles 

 avray. We have seen evidence that the valley 

 at Mount Morris was deepened by ice to the 

 extent of at least 200 feet. This would make 

 a difference of over a thousand feet between 

 the valley bottom at Mount Morris and the 

 bed of Lake Ontario. The advocates of north- 

 ward drainage will find it difficult to make 

 the preglacial Genesee descend this interval 

 in the space of seventy miles. Nor can they 

 appeal to constant deepening of the valley 

 northward, which would enable us to regard 

 the difference as due to tilting; for we have 

 seen that, instead of declining, the valley 

 bottom rises northward, until on the smallest 

 recorded rise it reaches very nearly the general 

 level of the country about Rochester. 



It is thus very evident that the valley of 

 Lake Ontario has been deepened far below 

 that of the Genesee and Canaseraga Valleys. 

 (The rock floor of the Genesee Valley at 

 Portageville, which on the hypothesis of 

 southward drainage is regarded as inde- 

 pendent of the Canaseraga Valley, is 1,500 

 feet above the deepest part of Lake Ontario, 

 the distance between the two points being 

 about ninety miles.) What has produced this 

 excessive deepening? Those who know the 

 region will not consider differential warping 

 as a factor: the dip of the strata scarcely 

 varies over this region. Ice erosion of the 

 Ontario Valley can not be appealed to, since 

 the course of the valley is nearly at right 

 angles to the movement of the ice. (The 

 question of ice erosion of the Ontario Valley 

 has been fully discussed by Gilbert, and more 

 recently by Grabau in the Bulletin on Niagara 

 Falls. Both authors agree that the evidence 

 does not favor the ice erosion theory.) Other 

 explanations, such as deepening by the solu- 



tion of the limestones are not favored by the 

 facts. The only satisfactory explanation 

 seems to be that Lake Ontario Valley was 

 deepened by normal river erosion. If that is 

 the case, and the preglacial streams of west- 

 ern New York flowed northward, and were 

 tributary to the Ontario River, their valleys 

 should have been deepened in conformity. 

 That they were not so deepened is a powerful 

 argument against the northward flow of these 

 streams. 



On the hypothesis of southward drainage 

 first advocated by the present writer, in 1901 

 (Bull. 45 N. Y. State Museum), and subse- 

 quently in this journal, the ancient valleys 

 of central and western New York must be 

 regarded as formed by streams arising in the 

 Canadian region, and flowing across New 

 York. They were gathered in by either the 

 Susquehanna or the Alleghany. This drain- 

 age developed upon an old peneplain which 

 beveled the strata, as shown by abundant evi- 

 dence (this is discussed quite fully by Grabau 

 in Bulletin 92, New York State Museum). 

 The development of this drainage system took 

 place in Tertiary time, when the land in the 

 north stood high, and the Mississippi embay- 

 ment and the Atlantic coast south of New 

 York were depressed. The evidence for this 

 is well known. The main stream of the 

 region was the Dundas, flowing out through 

 the Dundas Valley at the west end of Lake 

 Ontario. This stream was of the consequent 

 type, and one of its subsequents carved out 

 the broad Ontario Valley as an inner lowland 

 on the soft Siluric and Ordovicic strata. 

 This subsequent stream gradually beheaded 

 the streams flowing across New York, captur- 

 ing their headwaters, and carrying the drain- 

 age to the Mississippi embayment. Such a 

 stream would soon deepen its valley on the 

 soft Medina rocks, and thus the great sub- 

 sequent deepening of Lake Ontario would be 

 accounted for. This deepening, then, occurred 

 after the valleys of New York were cut, 

 these valleys remaining behind with beheaded 

 southward-flowing streams which were in- 

 capable of deepening or widening their valleys 

 any further. Meanwhile short northward- 

 flowing or obsequent streams came into exist- 



