Geology and Mineralogy. 187 
The yellow loam bed is for the most part between ten and twenty- 
five feet in thickness. “It is remarkable for the uniformity with 
which it appears at various levels, proving its deposition since the 
occurrence of a large amount of denudation in the older Bluff 
by a supposed barrier. 
e drift contains pebbles, which are mainly of reddish and 
yellowish chert. Among them there are numerous Silurian 
rachiopods; they must have come from Tennessee and the 
States farther north either side of the Mississippi river ; some of 
em from points 400 miles or more distant. The thickness of the 
drift in Louisiana is stated to average 200 feet. In the northwest- 
‘ 2 rot. 
nee “that the passage of this formation into the modified 
he N 
boulders of large size occurring at this elevation in Licking Co., 
Ohio; and on this point he adds; “ We are 
. Ssissippi valley, and must grant that when the water floated an 
ice raft either up or over a hill 1,159 feet above the present sea- 
el there was a clear sweep for the polar current from the straits 
of Belle Isle (Gulf of Newfoundland) to the Gulf of Mexico.” 
18 iceberg theory appears to be here called in just where it 
fannot serve. If the Gulf of Mexico had then opened up over the 
Continent either to the Arctic or the Gulf of Saint Lawrence, with 
the water 1,159 feet—or say 1,000 to 2,000 feet or more—deep at 
the Gulf, the Gulf stream would be the current, if any, that would 
“2ve occupied the great interior sea of the Mississippi valley ; and 
this would have given icebergs southward-bound a hard up-stream 
current to beat against. ere does not appear to be any good 
foundation for the conclusion that the Labrador current would 
