e 
152 Association of American Geologisis and Naturalists. 
Mr. Redfield had from his limited observations been led to 
infer that the drift of the region near New York 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 striz 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. 
ome 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 fe: 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 civilized 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 
ds 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. 
