JuLY 16, 1897.] 
fully examined such material for shells, but 
found no traces of them. These shells do 
not then belong toa preglacial fauna. The 
true interpretation of their history seems 
to be that there has been a retreat of the 
ice front some miles beyond its present 
position and a re-advance. 
The remaining problem is, to what was 
the retreat and re-advance due, and when 
did it occur? The retreat was probably 
caused by the general subsidence in the 
north which is indicated by elevated de- 
posits of recent shells in Baffinland, Grin- 
nell Landand Labrador. A depression which 
amounted to 1,000 feet in Grinnell Land, 
and affected all or nearly all of the Arctic 
archipelago and probably Greenland, must 
have greatly increased the water area in 
the north and caused a corresponding rise 
of temperature. This rise of temperature 
would undoubtedly cause a retreat of the 
glaciers, permitting the sea to extend 
much farther up the fjords than at pres- 
ent, and in the shells which the ice cap is 
now carrying from the valleys of the in- 
terior we have proof that such a retreat 
occurred. With the elevation of the land 
in the north again, a lower temperature 
prevailed and the ice recovered some of its 
former territory. 
KE. M. KInpte. 
YALE UNIVERSITY, December 8, 1896. 
CURRENT NOTES ON PHYSIOGRAPHY. 
THE SIERRA NEVADA. 
‘FuRTHER Contributions to the Geology 
of the Sierra Nevada,’ by H. W. Turner 
(17th Ann. Rept. U. S. G. S., 1896, 521- 
1076) contain many geographical items. 
Oroville table mountain is illustrated in an 
excellent plate. The deep, steep-sided can- 
yous that have been cut into the uplifted 
mass of the range often have benches on 
their slopes, caused by landslides; these, 
with the falls in the streams and the inac- 
cessible character of the canyons, may be 
SCIENCE. 93 
taken as features of a youthful stage of 
geographical development. Associated with 
them as indications of recent uplift are 
occasional fault scarps, still steep and bare ; 
one of these being shown ina plate. Of a 
little greater age are the fault-block lake 
basins, now drained by filling with sedi- 
ments and cutting down at the outlet; 
Meadow valley being of this class. Mo- 
hawk valley, first holding a Pliocene lake 
in a fault basin, was afterwards obstructed 
in Pleistocene time by fragmental andesite 
flows. Much of the volcanic material, once 
broadly spread over the Sierra area and 
now greatly dissected since its regional up- 
lift, is shown to be fragmental, coarse and 
fine, less or more stratified ; it is compared 
in origin to the mud flows of modern volca- 
noes. The flows came from the crest of 
the range, and ran for fifty miles on the 
comparatively gentle slope of the then low- 
lying region. The ‘hog-wallow’ mounds 
on the valley plain and margin of the foot- 
hills are described and illustrated, but not 
definitely explained ; they are one or two 
feet high, four to ten feet in diameter, and 
of the same pebbly soil as that on the in- 
tervening spaces. 
NORTH CAROLINA AND ITS RESOURCES. 
‘Norr Carorina and its Resources’ is 
the title of a volume published by the State 
Board of Agriculture (Raleigh, 1896, 413 
p-, many plates), to which the geographer 
may refer with profit. The mountains, 
with their minerals, mines, forests, and at- 
tractive ‘resorts ;’ the piedmont belt, with 
rich fields and great water powers, the 
coastal plain with its growing interests in 
truck farms and orchards, and the sounds 
with their fisheries, are all duly set forth. 
This report forms a fitting companion to a 
volume on ‘South Carolina, resources and 
population, institutions and industries,’ 
published some years ago by the State 
Board of Agriculture (Charleston, 1882). 
