mote possibility, therefore, that both maize and teosinte 
were growing at the time the deeper sediments were 
deposited. 
Although definite palynological and geologic conclu- 
sions have not yet been drawn as to the antiquity of the 
lowest portions of the Mexico City cores, the available 
evidence indicates that the sediments extend well back 
in Wisconsin time, most probably to the early stages of 
the Iowan advance of the Wisconsin Ice sheet.’ If this 
is the case, the fossil maize pollen with which we are 
concerned almost certainly antedates the practice of agri- 
culture in North America, and probably precedes the 
advent of man on this continent. 
1 Personal communication from Professor Paul B. Sears. 
[ 2389 | 
