152 Association of American Geologists and Naturalists. 



Mr. Redjield had from his Hmited observations been led to 

 infer that the drift of the region near New Yorli was the joint 

 result of glacial and aqueous action, and was mainly deposited 

 during a period of increasing submergence. Mr. Redfield also 

 alluded to the agreement of the striae of the polished rocks, and 

 of the transported bowlders and drift, with the known course of 

 the existing polar currents of the ocean, in the northern hemis- 

 phere ; and suggested that this system of currents, being essen- 

 tially the same in both hemispheres and having its cause in the 

 dynamics of the solar system, must have operated through all 

 time, and over extensive regions, but varying in locality and di- 

 rection with the changes of outline and relative levels of seas 

 and continents, during successive geological periods. 



Some discussion then ensued on the question whether the 

 mounds of the western United States were the result of natural 

 diluvial causes or the work of the Indians. 



Mr. Lyell cited an instance where the inhabitants of Scandi- 

 navia, had taken advantage of a long and very high natural ridge, 

 to form, three separate mounds, which they afterwards considered 

 as the burial places of their fabulous deities. 



Prof. Silliman remarked with respect to the genuineness of 

 mounds, as works of man, in contradistinction from those natural 

 piles, that have been cut out of the strata of clay, sand, gravel, 

 loam, &c.. and rounded and shaped by water so as to resemble 

 works of art — that artificial mounds (found in many and distant 

 countries, both on the eastern and western continent) appear to 

 have been characteristic of a particular state of society advanced 

 beyond barbarism, but not yet sufficiently civihzed for the con- 

 struction of massy sepulchres of solid stone, sarcophagi, pyramids 

 and temples. He appealed to those numerous mounds which 

 form a most impressive feature of the scenery on Salisbury plain 

 in Wiltshire, in the southwest of England. Prof. S. had counted 

 seventy of these mounds in one view, while sitting upon his horse 

 upon the top of a low one, and from the same place Dr. Stukeley 

 says that he enumerated one hundred and twenty eight. These 

 mounds are rarely less than thirty feet in diameter ; they are gen- 

 erally surrounded by a broad ditch, enclosed by a circular or ob- 

 long parapet or embankment. Near Overton in the west of Eng- 

 land, Prof. S. ascended one which was one hundred and seventy 

 feet high and whose base covered about an acre of ground, its 

 form being that of the lower segment of a cone. 



