316 THE JOURNAL OF GEOLOGY. 
NOMENCLATURE. 
The name “Grand Canyon Group” was given by Major J. W. 
Powell to the series of strata beneath the Tonto sandstone and 
above the “Grand Canyon Schists.’’ The latter were referred 
tentatively to the Eozoic,? and the 10,000 feet of the ‘‘Grand 
Canyon Group” to the Silurian. Captain Dutton regarded the 
series as of pre-Carboniferous age, and probably Silurian.’ 
In 1883 I referred the Grand Canyon series of Powell to the 
Lower Cambrian, and divided it into a lower and an upper group 
—the “Grand Canyon” and ‘“Chuar,” respectively,3 the name 
“Chuar” being proposed by Major Powell In 1886 the 
reference to the Lower Cambrian was changed to a pre-Cambrian 
series of rocks,5 and correlations were made with the Keweenawan 
series of the Lake Superior region. Ina section of the strata 
of the Grand Canyon District published in 18g0, the pre-Tonto 
strata were referred to the Algonkian group, under the names 
Chuar, Grand Canyon, and Vishnu, the latter including the strata 
unconformably beneath the Grand Canyon group.7 
At the present time it appears to be necessary to return to 
Major Powell’s name, Grand Canyon,’ as applied to the entire 
series of strata between the Tonto and the ‘‘Grand Canyon 
Schists,’’ and to give to the lower series the name Unkar, from 
the valley in which its finest exposures occur. The name Vishnu 
is retained for the unconformably pre-Unkar strata. The classi- 
fication, from the Tonto down, will then be: 
*Geology of the Eastern Portion of the Uinta Mountains, 1876, p. 70. 
? Tertiary History of the Grand Canyon District, 1882, p. 180. 
3Am. Jour. Sci., Vol. XXVI., 1883, p. 439. 
4 Loc. cit., p. 440. 
5 Bull. U. S. Geol. Survey No. 30, 1886, p. 41. 
Am. Jour. Sci., Vol. XXXIL., 1886. pp. 144, 153-157. 
7Bull. Geol. Soc. Am., Vol. I., 1890, p. 50. 
° Changing the spelling of “‘Cafion” to Canyon, in conformity with the decision 
of the Board on Geographic Names. 
