146 JOSEPH B. UMPLEBY 
surface; yet the area of granitic intrusions does not show a signifi- 
cant relation to surrounding sedimentary deposits until the Eocene. 
It is believed, therefore, that the granite intrusions accompanied 
the elevation which initiated that great cycle of erosion which 
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Fic. 3.—The figure shows the distribution of granitic rocks in the plateau 
region. Adapted from the Geologic Map of North America. 
resulted in the Eocene surface. The granite batholiths of the 
plateau region therefore are assigned to the late Cretaceous or 
early Eocene.” 
« Since this article was prepared, Mr. Adolph Knopf has told the writer that during 
recent field work he found the Butte granite to cut andesites which should probably 
be correlated with the Livingston formations. Mr. F. C. Calkins also has found 
the granite intrusions of the Phillipsburg quadrangle, Mont., to be post-Colorado. 
Thus recent geologic studies support conclusions and suggestions herein set forth. 
