go The American Geologist. Vebruary, 190%; 
I was able to gain some familiarity with the subject by per- 
sonal observation, but I can add nothing of importance to the 
work of others. I will briefly review the later Tertiary and 
Pleistocene history of the region and endeavor to fix as closely 
as possible the time of opening of the Sierran period. 
Topographically, the Sierra Nevada region is mainly di- 
vided among degraded fault-scarps, monadnock peaks, flat- 
topped divides, rolling uplands and cafions. Toward the 
north the latter two are quite distinct, but south of the Tuo- 
lume river, the surface is more deeply and broadly eroded, 
owing to greater tilting of the country and the topography is 
that of the “gulch and ridge” type. The dominating feature 
of all is the dissected peneplain, which is, over a large part of 
the area, so perfectly preserved and the evidence upon which 
its recognition has been based is so strong as to make it com- 
pare favorably in these respects with the best established pene- 
plains of the eastern states. 
It appears that late in the Tertiary era, erosion had re- 
duced the surface to an undulating plain across which the 
streams flowed in broad shallow valleys. Some disturbance, 
probably a slight depression, or possibly a slight elevation 
about their heads, caused these valleys to be filled up to the 
depth of fifty to two hundred feet and over, with alluvial 
gravel and sand, the well known Auriferous gravels proper 
or “high-level channels’” of that region. Then followed a 
period of vulcanism which may be divided into three epochs, 
known respectively from the most characteristic product of 
each, the rhyolyte, andesyte and basalt epochs. The tufts of 
the first are interstratified with the upper portion of the 
Auriferous gravels proper, but the andesyte tuffs unconform- 
ably overlie them. 
The Age of the Auriferous Gravels of the Sierra ‘Nevada. Jour. of 
Geol. vol. iv., Nov.-Dec., 1896. 
The Topography of California. Jour. of Geol., vol. v., Sept.-Oct., 
1807. 
The Ozarkian and Its Significance in Theoretical Geology. Jour. of 
Geol. Vol. vii., Sept.-Oct., 18900. 
The Drainage Features of Caliiornia. Jour. of Geo/. Vol. ix., Jan.- 
Feb., rgor. 
The Physiography of California. Bull. Am. Bur. of Geog., Sept. 
and Dec., 1901. 
Geologic Atlas of the United States. Text accompanying the Placer- 
ville, Sacramento, Jackson, Lassen Peak, . Marysville, Smarts- 
ville, Nevada City, Pyramid Peak, Dowineville, Truckee, Sonora, 
Bidwell Bar, Big Trees, Colfax and Mother Lode District sheets. , 
