8 
MODERN GEOLOGY IN AMERICA 
is, up to that date, the boldest stroke at universal correlation of 
geological formations ever attempted by earth-students. It is 
the first definite recognition of the two greatest geological ter- 
ranes found on our continent. It is the first chronologic compari¬ 
son of American Carbonic rocks with those of the typical locali¬ 
ties of the Old World. It furnishes the clue to all subsequent in¬ 
vestigations of the mid-continental region. It initiates a host of 
perplexing problems many of which are still unsolved. Where 
else in all the world have not the echoes of century-long contro¬ 
versy long since died away? 
The first geological map of the United States was published in 
1809. On it William McClure represents the great band of 
“alluvial deposits” in the Mississippi Valley as only reaching to the 
mouth of the Des Moines River. In a subsequent edition of this 
map, issued eight years later, the great tract of Secondary (Pale¬ 
ozoic) rocks touches trans-Mississippian domain. The corrections 
of the second edition of the map and the accompanying explana¬ 
tions, at least insofar as the extreme western parts are concerned, 
were doubtless due largely to the information imparted by travelers 
in the West at that time. It was the irony of Fate that McClure’s 
work, representing the very last of the old regime, should be cov¬ 
ered so closely by that of his colleague’s setting forth the first of 
the new. 
