Piedmont Plateau of Georgia. — Watson. 225 
it is that the acid eruptives [granites] were among the last 
igneous intrusions to disturb the rocks of the eastern Piedmont 
Plateau." The same author states in a preceding sentence, 
that the granite may have been intruded as late "as the last 
great disturbance of the region preceding the Appalachian 
uplift." 
After a study of the Newark rocks of the "Richmond basin" 
in Virginia, Shaler and Woodworth,* in commenting on the 
age of the underlying rocks or "fundamental plexus", including 
granites and gneisses, say, "they probably date to Laurentian 
or Huronian time." (p. 418). And again on nage 421 of the 
same report, the authors say, "The age of these rocks [granites 
and gneisses] is not locally determinable." The granites and 
gneisses of this area were grouped by Rogers!' as Archsean. 
Field and laboratory study of the granitic masses in the 
Georgia area certainly indicate, that they were not all con- 
temporaneous in origin. Some of them are pre-Cambrian, 
while others may possibly be later in age. The youngest acid 
intrusives could not have been later however, if as late, which 
appears improbable from the existing facts and conditions, as 
the last great Appalachian disturbance or uplift. 
Whatever age or ages be assigned the granites of this reg- 
ion, it is certain that the most massive types of the rocks exhibit 
strong proofs of mechanical strain, which indicates that since 
the intrusion of the last granites the region has suffered pro- 
found metamorphism. 
METAMORPHIC FORMATIONS OF NORTHWEST- 
ERN CALIFORNIA. 
By OscAK H. Hershey, Berkeley, Cal. 
INTRODUCTION. 
That portion of the Klamath mountains lying west of 
Shasta county, California, is not quite a terra incognita to geol- 
ogists, as it was visited by one of Whitney's exploring expedi- 
tions! and has since been partially studied by Diller, ? Fair- 
banks, il Anderson and the writer ; but all that has been written 
* ]9tli Annual Report. i'.S.deoI. Survey, ■IH97-9H (1899) Pt.ii. pp. 385-515. 
t Geology of the Virginias, iss-t. 
t Geological Survey of Cnlifornia, vol. i. 
S Fourteenth Annual Report, U. S. Geol. Sur. pp. 403-44-.T. 
jl Bulletin of the Geological Society n1 America, vol. vi, pp. 71-101. 
