THE GRAND CANYON OF THE COLORADO. 329 
formity by erosion, this was changed in 1886, and all the pre- 
Tonto strata were referred to a pre-Cambrian series." 
In the scheme of nomenclature adopted by the Geological 
Survey in 1888, the clastic rocks beneath the Cambrian and super- 
jacent to the Archean were grouped under the term Algonkian — 
of equivalent rank to Cambrian, Silurian, etc.2 In this classifi- 
cation the system name — equivalent to Paleozoic, etc. — was not 
decided upon; but I am strongly in favor of adopting the name 
‘“« Proterozoic,” proposed by Dr. Irving and accepted by Professor 
C. R. Van Hise.3 Under this nomenclature the Grand Canyon 
series will be referred to the Algonkian system of the Proterozoic 
group. 
There may be a difference of opinion among geologists as to 
the adequacy of the evidence that the Grand Canyon series is 
pre-Cambrian. This can hardly be the case with those who have 
studied the questions of orographic movement and subsequent 
erosion. The long section on the map shows most clearly that 
the sediments of the Grand Canyon series were elevated, faulted, 
and more or less flexed prior to the period of erosion that cut 
away a section of the entire series and not only reduced to a 
baselevel the land area formed by the latter, but reduced to the 
same plane the more resistant subjacent rocks of the Vishnu ter- 
rane of the Algonkian, and probably the Archean, to the west. 
The time required for the orographic movement resulting in eleva- 
tion and for the subsequent erosion would exceed, in my opinion, 
the period of Lower Cambrian sedimentation. It is not at all 
improbable that the sediments of Lower Cambrian time in the 
Great Basin region of Nevada, Utah, etc., were derived from the 
Algonkian continent to the east, of which the Grand Canyon 
series of rocks then formed a part. 
CORRELATION. 
The Grand Canyon series, the Llano series of Texas, and the 
Algonkian series of the Lake Superior region afford an opportu- 
*Bull. U. S. Geol. Survey No. 30, 1886, p. 41. 
2 Tenth Ann. Rept. U.S. Geol. Survey (for 1888-89), 1890, p. 66. 
3 Bull. U. S. Geol. Survey No. 86, 1892, p. 493. 
