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A, Homogeneous central mass of molten matter—probably meteoric iron. 
B. Region of Basaltic Lavas. 
C. Porphyries, Trachytes, ete. 
a. Return Trade Wind from S. W. to N. E. conveying frozen vapors. 
e. Polar current from N. E. to §. W., deflected sonth by mountain ranges. 
Upper curved line shows volcanic belt where the waters were vaporized at the close of the Tertiary Age. 
IDEAL SECTION OF NORTH AMERICA ON LINE OF FORTIETH PARALiLEL. (AFTER PROF. HITCHCOCK.) 
(SEE PAGE 123.) 
