Trans. N. Y. Ac. Sez. "30 Nov: 14, 
agent of erosion known. The eroding power of the ancient glaciers, 
which once reached southward to Trenton and Cincinnati, was attested 
not only by the planed down rocks, but by the immense sheet of 
transported debris left by the glacier in its retreat. 
The glaciated, planed, and polished rocks in the Western States are 
generally covered by a thick layer of clay, abounding in glaciated 
boulders. There are also other water-worn materials which have been 
transported, perhaps thousands of miles, representing the gravel bars 
sand beds, etc., produced by sub-glacial rivers. Although the mate- 
rials are entirely of glacial origin, all the stones are here usually 
rounded. We find in these deposits, called kames or eskers, the evi- 
dences of the action of running water produced by the melting of ice: 
their accumulation in heaps, ridges, etc., having been effected by local 
causes, waterfalls, streams upon or under the.ice, etc. 
The finer material produced by the same grinding action has been 
deposited along our coast in the vast masses of the Champlain clays. 
It is well known that the drainage of ali glaciers results in milky 
streams; é. g., those which descend from the Alps impart an opales- 
cence to the Lake of Geneva, and the streams from the Cascade 
Mountains are clouded with silt derived from the small glaciers at their 
heads. So, during the Glacial period all the fine material was sometimes 
washed out of the glacial drift, leaving banks and ridges, kames, hogs- 
backs, ete., of gravel and boulders, and carried by streams to the coast 
and there deposited along shore in the Champlain clays. The fine flour 
and bran ground by the glaciers have been sometimes referred to dif- 
ferent epochs, but they are produced simultaneously. The Glacial or 
Champlain clays are of great economical importance to the city, as they 
are the brick clays of Croton Point, Haverstraw Bay, and other points 
along the Hudson. Their thickness reaches 100 feet along the lower 
portion of the Hudson river, 400 feet on Lake Champlain, 500 feet at 
Montreal, 800 feet at Labrador, tooo feet at Davis’ Strait, and 1800 
feet at Polaris Bay. This indicates that the continent was depressed 
to this extent at each of these points, that the waters of the ocean 
extended through these valleys, and that here was dead water into which 
the glacier drainage flowed and was deposited. 
In the vicinity of New York City it is evident that the glaciers every- 
where over-rode and disregarded the underlying topography. All the 
surface of the island is strewn with materials derived from the N. N. 
W., and the rock has been planished and striated with grooves running 
in that direction. The hills back of Yonkers are covered by trap bould- 
ers, which have been conveyed across the river from the Palisade range 
on its western side; and it is plain that the glacier completely disre- 
garded the depression of the Hudson valley, filled it up to a greater or 
