Review of Recent Geologicdl Literature. 325 
river valley and led northward from it or perhaps continued across it 
eastward to the Red River of the North. 
Following this discussion there is a brief review of the Glacial period 
in North America and discussion of glacial deposits. A map of the 
glaciated area of North America sliows the position of the "Wisconsin" 
boundary as well as the older Glacial boundary and of lakes Bonneville, 
Lahontan and Agassiz. The courses of glacial movement are indicated 
more completely than in any map of North America before published and 
several pages of text are covered with a list of striae in the north part 
of the continent, presented as an appendix to the volume. The shifting 
or change in direction of ice currents in Minnesota and neighboring- 
districts, which was brought to notice some years ago by Mr. Upham, 
is here treated in connection with a description of the several moraines 
of the Wisconsin sei'ies. Very little attention is given the older drift 
sheets of America, and the intervals of deglaciation by which they are 
separated from each other and from the Wisconsin drift. As a conse- 
quence the discussion may give the impression that the production of 
the Wisconsin series of moraines occupied the greater part of the 
Glacial period, a view which the author would certainly notvvish to 
maintain. 
The history of lake Agtissiz which forms the central theme of the 
paper is introduced by a brief reference to the evidence by which the 
former existence of glacial lakes is recognized, five evidences being 
noted as follows: (1) Their channels of outlet over the present water 
parting; (2) cliffs eroded along portions of the shore by the lake waves: 
(3) beach ridges of gravel and sand; (4) delta deposits formed by in- 
flowing streams; and (5) fine sediments spread widely over the lacus- 
trine area. Of these evidences the one most definite in its testimony to 
the influence of the ice sheet is the lake outlet. These outlets in sev- 
eral cases are found leading away from basins which are now drained 
by continuous descent in the opposite direction. The basins present 
no indication that the lakes were formed by any land barrier across 
their lower portions, which has since been removed by erosion or by 
depression. The case is made very strong where shore lines that con- 
nect with the former outlet are found to rise in elevation when traced 
toward the present outlet instead of sinking in that direction, as they 
would do if there had been a removal of the barrier by depression. 
That such is conspicuously the case with the shores of lake Agassiz 
has been brought to notice in earlier papers by Mr. Upham and is well 
shown in the course of this monograph. In view of this clear evidence 
against the occurrence of a land barrier it seems i-emarkabJe that the 
hypothesis of a land barrier, as the cause for lake Agassiz, should have 
been favored by professor Dana in the last edition of his Manual. (See 
pp. 947-948, 985-98G). Lake Agassiz is but one of several glacial lakes 
which existed in the northern United States and Canada and the oc- 
currence of several of these glacial lakes is briefly touched upon by Mr. 
Upham. 
Evidence is produced to show that lake .Agassiz became graduallv 
