Tertiary and Quaternary Baseleveling. — Upham. 2W.) 
The duration of the earlier baseleveling apparently coin- 
cided, as to both beginning and end, with the Tertiary or 
Somerville cycle of partial baseleveling which Davis and 
Wood have studied in Pennsylvania and northern New Jersey 
and believe to have affected a large area of the other eastern 
states.* The termination of the denudation forming the 
western plains, and their uplift to undergo the erosion of the 
Red river valley and of the present Assiniboine and Saskatch- 
ewan valleys, were probably also contemporaneous with the 
great epeirogenic movement which in California, according to 
Mr. J. S. Diller, ended a long cycle of baseleveling that had 
extended through the whole of Cretaceous and Tertiary time, 
and raised a part of that baseleveled district at the beginning 
of the Quaternary era to form the lofty Sierra Nevada. t 
Again, the same record of long continued baseleveling, fol- 
lowed by uplift and a new c}*ele of rapid valley-erosion, is 
found by Powell* and Duttonjj in the plateaus and Grand 
canyon of the Colorado. The broad denudation above these 
plateaus, when compared with the studies thus noted in other 
regions, and with the total erosion of the canyon seems to have 
required not only the Eocene and Miocene periods, but also 
most of the Pliocene; for the ratio of the denudation to the 
canyon-cutting must be nearly or quite as great as that between 
the duration of the entire Tertiary era and the comparatively 
short time since its close. Instead of referring the division 
of these parts of the history of the Grand Canyon district to 
the beginning of the Pliocene, as was done provisionally by 
Dutton, it may therefore mark the final stage of the Pliocene 
period and the inauguration of the Quaternary era. In the 
southern and eastern United States, according to McGee, u 
similar great uplift of the land, with very extensive erosion. 
•Proceedings, Boston Society of Natural History, vol. x.xiv. L889, pp. 
::<;:)-}•,':;. National Geographic Magazine, vol. i, 1889, pp. 183-253; vol. 
ii. 1890, pp. 81-110. 
U.S. Geol. Survey, Eighth Annual Report, lor l886-'87, pp. 128-432. 
Journal of Geologj*, vol. ti, pp. 32-54, Jan. -Feb., 1894. Compare also 
articles by Prof. Joseph Le Conte, Am. .lour. Sci., Ill, vol. xix. pp. 176- 
L90, March, 1880; vol. xxxii, pp. 167-181, Sept., 1886; vol. xxxvm. pp. 
257-263, Oct., 1889. 
{Exploration of the Colorado River'of the West, 1875. Geologj of the 
eastern portion of the Uinta Mountains, 1 s ? « ; . 
py. S. Geol. Survey, Monograph n. "Tertiary Historj of the Grand 
Canon District." 1882. 
