330 THE JOURNAL OF GEOLOGY. 
nity of comparing the stratigraphic succession of somewhat sim- 
ilar lithologic series of strata, but a definite correlation can nct 
be made until a more reliable factor is obtained than lithologic 
resemblance of the various formations. It is quite probable thet 
the Grand Canyon series and the Keweenawan series of Lake Supe- 
rior represent the same time-interval; also that the strata beneath 
Packsaddle Mountain, in central Texas, are the equivalent of the 
Chuar terrane of the Grand Canyon; but until paleontologic 
evidence is secured it may be said that these correlations are 
little more than possibilities. The Grand Canyon, Llano, and 
Keweenawan series may be referred to the Algonkian, as that 
system of rocks includes the strata of sedimentary origin between 
the Archean complex and the base of the Cambrian; beyond 
that any correlation on trustworthy data is impossible. Mr. 
Iddings’s examinations of the specimens of eruptive rocks in the 
Algonkian of the Grand Canyon series show the basal flows of 
the Unkar terrane to be a true doleritic basalt, and that the dikes 
and the upper flows, as exposed in Chuar Butte, etc., are basalts 
differing but little from the basalts of Tertiary age found in 
Nevada, Utah, and on the plains in the vicinity of the Grand 
Canyon. This fact prevents any correlation of the lavas with 
those of other localities, even though basaltic rocks were found 
to occur in formations referred to the Algonkian. It is evident 
that until characteristic fossils are found in the various terranes 
now referred to the Algonkian it will be impossible to make any 
correlations that will be more than tentative suggestions. 
CHARLES D. WALCOTT. 
