Hie GEOLOGlCAE HLS TORY TOke NE We OURS SibAT Ey 83 
It is practically certain that preglacial streams were here north- 
flowing rather than south-flowing, because during long Tertiary 
time such tributaries to the large stream in the Ontario basin must 
have developed across the steep north slopes of the Niagara and 
Helderberg escarpments, and also because the slope of the Genesee 
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Fic. 27 Grabau’s interpretation of late Tertiary drainage in the eastern 
Great Lakes region, the intention being to show the general kind of drainage 
rather than the exact location of the streams. The “Rome” river with 
source at Little Falls is well shown. The three south-flowing streams should, 
in the writer’s opinion, be represented as north-flowing, at least immediately 
prior to the great Ice Age. 
After Grabau, N. Y. State M s. B-1. 45, fig. 6 
Tiver is now, at least, so decidedly downward toward the north. 
If the late Tertiary Genesee flowed southward, the reversal of its 
course must have been caused by a very marked tilting of the land, 
but we have no evidence for such a decided land movement. 
{n our discussion of Mesozoic drainage (see chapter 5) we found 
that, during the early part of that era, nearly all the drainage of 
