304: REPORT OF THE AMERICAN COMMITTEE. 
the ice age rather than elevated. 5. The Long Island ridge 
represents the extreme southern margin of the ice sheet. 6. The 
agency of icebergs and shore-ice in producing boulder clay is 
conceded for the lower St. Lawrence valley as high as the Saxi- 
cava sand. 
Lower 3Iississippi Valley. 
The enormous mass of sediment discharged into the Gulf of 
Mexico by the Mississippi river, and the situation of the upper 
part of the hydrographic basin so as to collect the water derived 
from the melting of the ice-sheet, give peculiar and, in one sense, 
typical Plistocene deposits. Prof. T. C. Hilgard has given a 
summary of ten years' study of them. 
At the base, Orange sand or stratified drift, 60 to 100 feet thick, 
supposed to be the equivalent of the northern till. Second, the 
Port Hudson swamp and littoral deposits, from 30 to 630 feet 
thick, supposed to be the equivalent of the Champlain period as 
defined by Dana. Third, Loess or Bluif, and Loam, 50 feet. 
Fourth, Alluvium and mudlumps, 30 to 70 feet. 
The Orange sand has a large development in Mississippi and 
Alabama, being most abundant at the present heads of naviga- 
tion in the rivers, where the highlands begin to rise noticeably. 
It is analogous to a flood-plain deposit, some of the material 
having been carried 60 to 80 miles in Alabama. Tuoraey was 
the first to suggest some affinity of these sands to the northern 
glacial deposits, and conjectured that they might be traced as far 
north as Baltimore. This would seem to be confirmed by the 
observations of McGee in the establishment of the " Appomattox 
formation." 
Quaternary of the Inferior. 
Since the discovery of the two lines of terminal moraines from 
the Atlantic to Dakota, the science of Surface Geology has fairly 
been reconstructed. No organization has accomplished so much 
in this direction as the United States Geological Survey. With- 
out tracing the various stages of discovery, it will be sufficient to 
give the latest conclusions of Prof. T. C. Chamberlin as to the 
events and order of deposits. The table is somewhat abridged. 
The transition epoch from the Pliocene is not yet satisfactorily 
distinguished. 
