PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 469 



Would grind up rocks and spread their huge fragments over the 

 continent, and leave a deposit of such depth. One consequence has 

 been that upon the south or southwest of every isolated mountain 

 there is a gravel bed, and there the farmer finds his richest land ; 

 because there is the greatest accumulation of those materials, 

 lime, sand, alumina, with which the drift period has enriched this 

 portion of the American Continent.* 



The Chairman stated that he had been informed by a man who 

 had spent his life in trading in lands that he had formed the rule 

 never to bu}^ land upon the north side of hills or mountains ; 

 that all the best lands lay to the south of them. He had himself 

 observed the same fact; and that the forests are generally left to 

 grow upon the northern sides of the hills. 



Mr. Stevens stated that since the discovery of a mammoth in 

 Siberia clothed with fur four inches long, outside of which was 

 coarse rank hair twelve or fourteen inches in length, geologists 

 were modifying their views with reference to the temperature of 

 the earth in former ages. Animals may be allied to our tropical 

 animals, and yet may have been fitted to endure an Arctic 

 climate. 



The Chairman. — Is there any geological reason why there 

 should be a greater abrasion upon eastern than upon western 

 slopes ? 



Dr. Stevens. — Yes ; the rocks were fractured upon the eastern 

 slopes. 



DREDGING. 



Mr. John Johnson explained his new method of dredging, which 

 he illustrated by numerous experiments. He gave a brief sum- 

 mary of the early machines used in dredging. In 1591, there 

 was a machine used in Italy scooping up the materials which 

 were desired to be removed for the benefit of navigation. In 

 1618, Savery took out a patent in England for the application 

 of steam to dredging. In 1708, Hertel, and in 1734, Morton and 

 Balrae, of Holland, employed a barge, and a windlass to draw up 

 the materials collected by a spoon and bag. In 1750, iron buckets 

 and an endless chain arrangement, were used in France. In 1774 

 to 1780, Redelykhead and Eckhardt applied scoop wheels. John 

 Golburn, of Chester, had already, in 17G8, used a kind of scoop 



* This may be true of an isolated mountain; but is contrary to the great fact that 

 nearly all the richest lands of the United States lie north and west of the Appalachian 

 group. — J. R. 



