Crosby.] 
466 
[Jan. 15, 
great earth movements at these times elevated portions of the 
globe’ to such heights that they had cool climates with most of 
their precipitated moisture as snow instead of rain. Deformation 
of the earth was doubtless the means of its relief from the strains 
due to its continuous contraction during the ages of quietude be- 
tween epochs of mountain-building ; and the extent of the defor- 
mation would be greatest, elevating extensive areas as high pla- 
teaus, just before the plication of sections of the earth’s crust 
and their upthrust as mountain ranges. These culminations of 
the effects of terrestrial contraction Mr. Upham finds, associated 
with the Carboniferous and Permian glaciation, in the folded Ap- 
palachian ranges of eastern North America and the Sinian moun- 
tains system of eastern Asia, both formed in the Permian period 
and constituting parts of the grandest disturbances of the earth’s 
crust between the end of the Archaean era and the beginning of 
the Quaternary. Again, the latest and probably most extraordi- 
nary glacial period that our earth has passed through is known to 
have been attended by uplifts of the Cordilleran ranges in both 
North and South America, and especially by mighty throes of 
mountain-building in the Himalayan chain and considerable dis- 
turbances along its western continuation in the Caucasus, Alps, 
Pyrenees, and Atlas mountains. 
Thus the chief cause of the climatic changes producing ice- 
sheets and local glaciers seems to be found in the elevation of 
broad areas for the former, and of mountain districts for the lat- 
ter, to heights much above their present levels, bringing cooler 
temperatures throughout the year. On the other hand, the return 
of warmth and departure of the ice were coincident, at least in the 
case of the Quaternary ice-sheets, with subsidence of the glaciated 
portions of the earth’s crust, which indeed appears to have been 
due to the weight of the ice and to have become in turn the princi- 
pal influence leading to amelioration of climate and the final gla- 
cial melting. 
Prof. W. O. Crosby referred briefly to some examinations of the 
till or bowlder clay in the vicinity of Boston which he has made 
during the past year with a view to determining the normal pro- 
portions of mechanical detritus (bowlders, pebbles, sand and rock 
flour) and the residual product of chemical decay (clay) in its 
composition. The rock flour, which must be ascribed mainly to the 
