604 REVIEWS 
The St. Lawrence outlet is a complex of three partly submerged valleys. 
The straits between the islands mark sags in the inter-basin ridges. The 
former drainage of the locality was southwestward across the basin of 
Lake Ontario, in the edge of which many of the pre-glacial channels may 
be detected by sounding. C. W. W. 
Moulin Work Under Glaciers. By G. K. GmLBERT. (Bulletin of the 
Geological Society of America, Vol. XVII, pp. 317-20, plates 
40-42.) 
Describes, figures, and explains the formation of some interesting 
examples of complete and incomplete glacial pot-holes. 
C. W. W. 
Gravitational Assemblage in Granite. By G. K. GILBERT. 1900. 
(Bulletin of the Geological Society of America, Vol. XVII, 
pp: 321-28, Plates 43—46:) 
The author suggests that gravity may have caused some aggregations 
of feldspar, and of hornblende, in certain granitic rocks of the Sierra 
Nevada. The only evidence offered is the observation that these aggre- 
gates of phenocrysts are of materials, lighter in one case, heavier in the 
other, than the rest of the rock; and that there is little granitic material 
between the phenocrysts. 
Some banding observed in the granite is assigned provisionally to depo- 
sition under gravitational control. An “‘unconformity” in this granite is 
described and photographed (p. 324, Fig. 1, and Plate 44). This is thought 
to be due possibly to internal magmatic deposition and erosion. 
C. W. W. 
Post Pleistocene Drainage Modifications in the Black Hills and Big- 
horn Mountains. By GEORGE RoGERS MANSFIELD. Cambridge, 
Mass., 1906. (Bulletin of the Museum of Comparative Zodlogy,, 
Vol. XLIX; Geological Series; Vol. VIII, No. 3; pp: -59-87-) 
Extensive high deposits of Pleistocene river gravels are described in 
both districts. The former general courses of the streams that deposited 
these gravels is determined by an ingenious plot (Plate I) on which each 
gravel locality is connected with the possible sources of its pebbles. The 
modification of the Pleistocene stream courses through adjustment, cap- 
ture, and crustal warping is discussed. The entrenchment of the streams 
in post-Pleistocene time is assigned ‘‘to uplift or broad up-warping, rather 
than to climatic oscillation.” C. W. W. 
