Personal and Scienti^o News. 123 
Davis, and ]Mesprs. T. T. Bouve. Warren Upham, Frank Leverett, and 
others. 
In opening the discussion Mr. Upham outlined the geolofiic proofs of 
the former existence, within the Quaternary era, of ice-sheets on the 
northern half of North America and nn northwestt^rn Europe, as shown 
by transportation of drift and the formation of terminal moraines. The 
maximum thickness of the ice-sheet of the northeast part of this conti- 
nent was about two miles, according to D;ina, and in British Columbia 
Dr. G. M. Dawson's observations show that country to have been cov- 
ered by an ice-sheet whose central portion was a mile thick ; but the 
Rocky mountains had only local glaciers, which probably became 
confluent witli the ice-sheets on each side. Toward the northwest the 
extent of the ice has been defined by the explorations of Russell and 
McConnell, who find that southern Alaska and the wiiole course of the 
MacKenzie bear marks of glaciation, while these are absent along 
the Yukon excepting near its sources. The climate most favi rable for 
the accumulation of ice in such thickness upon the land would be dis- 
tinguished from the present by plentiful snowfall during more of the 
year than now, the surplus aliove thefimount melted in summer being 
slowly gathered during thousands of years to form the ice-sheets. The 
departure of the ice and incoming of the present climatic conditions 
was rapid, as is inferred from the scanty erosion by wave-action and 
accompanying formation of small beach deposits on the shores of the 
glacial lake Aga^^^siz, in comparison with the liiy:h cliffs eroded in till 
and tlie exten.-^ive resultant deposits of dune sand on the I'orders of 
lake Michigan. The latter have been in process of formatirn during 
the whole post-glacial epoch, but its duration, as measured by the re- 
cession of Niagara and St. Anthony's frdls and by the present rate of the 
drifting of sand along the lake shore at Chicago, seems to have been 
not more than 7,000 to 10.000 years. Lake Agas.-iz, caused by the 
barrier of the receding ice-sheet, coidd not have existed so long as this ; 
and therefore tlie glacial retreat along the Red river valley and by 
lake Winnipeg to Hudson bay is known to have been geologically sud- 
den. It was, however, attended by the accumulation of numerous 
morainic belts which denote halts or stages of some re-advance, inter- 
rupting the (.'eneral recession of tlie ice. 
Professor Wright spoke of the Quaternary lava outflows of California , 
Oregon, Washington and Idaho, one of the lava sheets being penetrat- 
ed in the upper part of the section overlying the Nampa image ; and 
he inquired whether the volcanic action may have been one of the 
causes of the amelioration of climate at the end of the ice age. 
Professor Putnam referred to the traces of man's presence at the 
time of both the later and the eailier drift deposits of this country, 
and the contemporaneous existence of the mammoth and mastodon 
during the glacial period in the re;j:ion south of the ice-sheet and their 
return northward when temperate conditions were restored. 
Mr. Leverett stated that the forest bed lietween deiiosits of till in 
Indiana and Illinois i>roves an interglacial epoch between the maxi- 
mum extension of the ice-sheet in the Mississippi b;isin and its incur- 
sion when the moraines of that area were formed, the intervening 
recessions of the ice being to a distance at least two-hundred miles 
north of the outer moraine. The climatic conditions of the period are 
thus known to have swayed from severity to mildness repeatedly. 
Professor Crosby gave some results of his recent investigations as to 
the state of mechanical division of the tine portions of the till and its 
comparatively small ingredient of true clay. His inference is tiint the 
proportion of the drift sup])lied from preglacial rock-decay is much less 
than that derived from the l)ed-rocks by glacial erosion; and that the 
decomposition of the rocks there had been less profound than in the 
