104 The American Naturalist. [February, 
THE INFERIOR BOUNDARY OF THE QUATERNARY 
: ERA. 
By Oscar H. HERSHEY. 
The great diversity of physical conditions of the earth’s 
surface in the Quaternary era of its geological history, has 
been conducive to much legitimate difference of opinion 
among students as to the most natural boundaries of the era. 
A few consider it proper to commence it at the opening of de- 
position of the now well known Lafayette formation. A few 
others, the writer included, would date it from the close of the 
Lafayette epoch of aggradation in the coastal plain and Mis- 
sissippi embayment regions. But the larger number of geolo- 
gists are accustomed to refer its beginning only as far back as 
the first marked extension of land ice in North America and 
Europe, namely, to the opening of the Kansan epoch. It is the 
purpose of this paper to defend, if possible, the intermediate 
proposition. 
The Quaternary era, as limited by many geologists, was 
characterized by a great extension of land ice in the form of 
broad névés passing into and bordered by vast glaciers. As 
known from their effects, these masses of glacial ice were of 
great extent, covering at their maximum expansion millions 
of square miles of the northern temperate zone, and having 
great development on other parts of the earth’s surface, nota- 
bly in the southern portion of South America, and on nearly 
all high mountain ranges even under the equator. But be- 
tween the several maxima of cold, producing and in part pro- 
duced by these glaciers, there seem to have been climatic 
periods of comparative mildness. These are commonly known 
as interglacial epochs because the deposits which belong to 
them are frequently found interbedded with those which are 
due to direct ice action, and also because they separated the 
several epochs whose most characteristic condition was glacia- 
tion. But the interglacial epochs were longer than the alter- 
nate glacial epochs, so that in point of time, the Quaternary 
