Modified Drift and the Cha»iplai/i Epoch. — Uphaui. 319 
MODIFIED DRIFT AND THE CHAMPLAIN EPOCH. 
By Warren Upham, St. Paul, Minn. 
Some American glacialists prefer other terms instead of 
these presented in the foregoing title; and one of the latest ex- 
pressions of such preference is by my friend, Mr. J. B. Wood- 
worth, in his paper, "The Ice-contact in the Classification of 
Glacial Deposits" (Am. Geologist, xxiii, 80-86, Feb., 1899). 
That paper, in accordance with general usage, includes all the 
products of glaciation under one comprehensive name, drift, 
whether directly laid down by an ice-sheet or removed from 
the ice and deposited, after being more or less worn and as- 
sorted, by the running water of the glacial melting and of rains 
or by the laving action of adjoining lakes or the sea. 
For the two primary classes of the drift, distinguished thus 
genetically in the conditions of their deposition, I believe that 
the contrasted terms, glacial drift and modified drift, which 
have been long in use, are the most expressive, euphonious, 
and serviceable. To show reasons for the retention and gener- 
al acceptance of these terms is the purpose of the earlier and 
principal part of the present paper. In its later part, attention 
is directed to the value in chronologic classification, and to the 
large significance, of the Champlain epoch, during which (as 
the term has been used by Dana, C. H. Hitchcock, Le Conte. 
and others, including the present writer) the modified drift, 
marginal moraines, and apparently the greater part of the till, 
were deposited upon the glaciated regions of North America 
and Europe, excepting only comparatively small outer areas, 
which were ice-enveloped in the early or middle parts of the 
Glacial period, but not in its closing stages constituting the 
Champlain epoch. 
Glacial Drift. 
The first great class of drift deposits, formed by the ice 
alone, which Woodworth calls the "till group," includes some 
varieties which cannot be regarded as till, the most noteworthy, 
perhaps, being belts and shorter tracts of very abundant bould- 
ers forming parts of moraines or closely associated with mor- 
aines of ordinary till and kames. Hence it seems to me prefer- 
able that this class or group be called glacial drift, noting the 
method of origin and deposition of its several formations, as 
(i) subglacial till, including usually the chief mass of the drift 
