Q2 NEW YORK STATE MUSEUM 
erosion in the Black river valley, and figure 35 is a structure sec- 
tion across the valley showing the rock terraces and the relations 
of the various rock formations. The high, steep, terrace fronts 
are certainly young topographic features which could not have been: 
present at the close of the long preglacial erosion period, nor could 
they have been formed since the Ice age because glacial deposits, 
even near the valley bottom, have not yet been removed. There is 
still the possibility that glacial waters may have done the work, 
but there is no evidence for such vigorous water action especially 
on the higher part of the Trenton limestone terrace where records 
would surely be left. On the contrary, there are glaciated rock 
surfaces and also glacial deposits (kames) on the great limestone 
terrace and near the base of the steep front of the shale terrace, 
so that the work could not have been done by glacial waters before 
the ice retreat. Evidently, we have here a fine example of ice 
erosion, and before the Ice age the limestones and shales extended 
somewhat farther eastward than they now do. The conditions for 
ice erosion were here unusually favorable because the ice, in its 
great sweep around the Adirondacks, was shod with many frag- 
ments of very hard rocks and entered the deep Black river valley 
striking with greatest force against the soft sedimentary rocks of 
the west side of the valley. As the figure clearly shows, the very 
soft shales were worn back more than the harder limestones, while 
the very hard Precambric rocks were very little affected. This is 
perhaps the best example of ice erosion in northern New York, and 
even here we must admit that only soft rocks were much eroded 
and that the great preglacial Black river valley was comparatively 
little modified. If soft shales had made up the valley bottom, ice 
erosion would have caused considerable deepening as was, no doubt, 
the case in the valleys of the Finger lakes region. 
Most of the Adirondack mountain peaks, especially the more 
isolated ones, were thoroughly scraped off and rounded down to 
the very live or fresh rock (see upper. view, plate 17), while the 
favorably situated valleys were vigorously glaciated by the removal 
of all the rotten and at least some of the fresh rock, especially 
when this latter was the comparatively soft Grenville limestone. 
Such phenomena are particularly well exhibited in Warren county 
(see figure 13) where the landscape is characterized by many great, 
glaciated rock domes which rise above the valleys of weak Gren- 
ville. In a few cases where the ice moved directly across deep 
valleys, like that between Lake George village and Warrensburg, 
the rotten rock to great depth may still be seen in its original place. 
