Atal THE JOURNAL OF GEOLOGY. 
apparently justified, and that the age of the series is probably 
Silurian; also that Devonian beds may be found in its upper part, 
but all that he could say then was that they are pre-Carboniferous. 
He called attention to some layers among the higher beds of the 
series which he did not hesitate to pronounce volcanic rocks— 
basalts or diabases. They are coal black and interbedded with 
the Upper Silurian (?) strata, but whether they are intrusive 
sheets or contemporaneous coulées outpoured while the rocks 
were accumulating, he could not say. 
During the winter of 1882-83 I studied in detail the Grand 
Canyon series of Powell, and found that it was, as stated by the 
latter, unconformably beneath the Tonto sandstone. The lava 
beds, however, were found to be interbedded and contemporaneous 
with the deposition of the Grand Canyon terrane and 6000 feet 
below the summit of the series. Ina preliminary note published 
in 1883, the Grand Canyon series of Powell is divided into a 
lower or Grand Canyon group and an upper, the Chuar group. 
As traces of fossils were found in the Chuar terrane, it and 
the Grand Canyon terrane were referred to the Lower Cambrian. 
The subjacent unconformable strata were referred to the Archean, 
and by reason of stratigraphic position they were tentatively 
correlated with the Keweenawan group of Wisconsin.’ 
In 1886 the Grand Canyon and Chuar terranes were referred 
to a pre-Cambrian series of rocks;3 and in 18go, in describing 
the Butte fault, a diagrammatic sectiont and several detailed 
sections that included portions of the Chuar and Unkar terranes 
were published.5 
In his correlation paper on the Archean and Algonkian rocks,° 
* Pre-Carboniferous strata of the Grand Canyon of Colorado: Am. Jour. Sci., Vol. 
XXVI, 1883, p. 440. 
? Loc. ctt., p. 441. 
3 Am. Jour. Sci., Vol. XXXII, 1886, p. 144; Bull. U. S. Geol. Survey No. 30, 1886, 
p. 41. 
4Tenth Ann. Rept. U. S. Geol. Survey, 1890, p. 551. 
5 Bull. Geol. Soc. Am., Vol. I, 1890, pp. 51-56. 
© Bull. U. S. Geol. Survey No. 86, p. 507. 
