Trans. N. V. Ac. Sa'. 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 all glaciers results in milky 

 streams ; e. §■., 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, leaying banks and ridges, kames, hogs- 

 backs, etc., 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, 1000 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 



