312 The American Geologist. ^^'^'^ ^'■^^'^■ 
them. Lakes formed in the new valleys and received sediments 
similar to those of the preceding period. 
The age of the second lake- forming period is vaguely re- 
ferred to late Tertiary. From structural and stratigraphic evi- 
dence the beds are younger than the lake sediments of Death 
valley, and they are certainly older than the gravel deposits 
which mark the Pleistocene period in this region ; therefore, 
they are provisionally classed as Miocene and younger. 
EDITORIAL COMMENT. 
HOW LONG AGO WAS AMERICA PEOPLED? 
To glacial geology, as much as to archaeology and ethnol- 
ogy, must we look for the answer of this question. On this 
continent, glacialists find evidences of man's presence only 
during the late and closing stages of the Ice age; but the Old 
World has good proofs that man was there, making and using 
stone implements, contemporaneous with the oncoming of 
that age, when an ice-sheet enveloped the northern half of 
continental Europe and the greater part of the British Isles, 
reaching south to the upper courses of the Don and Dnieper, 
to the lower Rhine, and to the Thames. Any estimate of the 
antiquity of man, therefore, whether in the western or the 
eastern hemisphere, must depend on the measures or estimates 
obtained by geologists for the duration of the Postg'la.cial 
period, and of the much longer Glacial period. 
For the time since the end of the Ice age, apparently nearly 
aHke in America and Europe, approximate determinations 
have been given by N. H. Winchell, G. F. Wright, and many 
other glacialists, as summarized by Hansen, which range from 
5,000 to 12,000 years. Their average, or about 8.000 years, 
may be confidently accepted as near the truth. 
It is more difficult to secure a probable estimate, on which 
glacialists will so well agree, for the length of the Glacial per- 
iod, which is found on both continents to have been very com- 
plex and long, as measured by years, though r>hort in compar- 
ison with preceding geologic periods. On both tliese vast land 
areas it involved nearly the same sequence in the stages of 
