56 The American Geolorjisf. January, 1895 
trjiU'd ill llic frontispiece <ind text descriptions, may be due, in some 
places wiiere it is most complex, to changes in the directions of currents 
in ont^ and the same ice-sh(>et on the same urea at different times, such 
as are found to iiave prevailed in eastern and northeastern Minnesota, 
being there comprised wholly within Prof. Chamberlin's latest or East- 
Wisconsin division of the declining part of the Ice age; and the inter- 
glaciai fossil iferous beds of Toronto and Scarboro. Ont., seem referable 
to a stage in the glacial retreat when lake Iroquois, the glacial represen- 
tative of lake Ontario, had begun to outflow by Rome, N. Y., to the Mo- 
hawk and Hudson rivers, after which the (^i)eirogenic uplifting of the 
Rome outlet caused the lake level at Toronto to rise to the high Iroquois 
beacli, the glacial readvance that covered the fossiliferous delta beds 
having been i)robably only a moderate liuctuation of the ice-front, till 
this time lingering on tlie highland between Toronto and (Jeorgian bay. 
Nearly half of North America, or an area of 4,000.000 scpiare miles, 
was ice-covered. It will be very interesting to learn, from Prof. Cham- 
berlin's observations in northwestern Greenland and from future e.xplo- 
rationsof the Arctic archipelago, whether this continental ice-sheet was 
confluent over (irinnell land and Smith sound with the Greenland ice. 
The terminal or retreatal morainesof the Laurentidc portionofthe North 
American ice-sheet, traced across the norlheni I'nited States to the 
northwestern plains of Manitoba and Assiniboia by Chamberlin, Smock,. 
Lewis and Wright, Todd, Leverett, Salisbury, Upham, and others, af- 
ford most imjjressive proof of the land-ice origin of our drift; and these 
twelve to twenty or more moraines, marking p.iuses in the glacial re- 
cession, are accei)led as all belonging to the closing part of the whole 
history of the Ice age. 
The distinction of the successive portions of the North American gla- 
cial drift in the order of their age by geographic names, as the Ka/isan, 
East-Ioimn, and Kaxt- Wisconsin formations, here proposed by Prof. 
Chamberlin, seems to be clearly a step of progress. It would perhaps be 
better, however, for reasons of euphony, to shorten the two latter names 
simi)ly to loirdii and Wuro?mn, whicli, with their definitions, will be 
suHiciently understood. This system of nomenclature is elastic, permit- 
ting interpolation and elimination, and it leaves the question o|)en for 
further investigation and discussion, whether the Glacial period was 
dual, threefold or tnore complex, with one, two or more intergiacial ep- 
ochs, or, on the other haiul, was essentially continuous, with compara- 
tively small oscillations of the ice l)oundarirs during both the growth 
and decline of the ice-sheet. 
Concerning the caii.ses of glaciation, Profs, (ieikie and Chamberlin 
doubt the adeipiacy of Dr. ('roll's astronomic theory, which a few years 
ago obtained more general assent: but they fail thus far to approve the 
alternative epeirogenic theory of Dan.i. I.e Conte. Wright, Cpham. 
•lamieson, Palsan and others, which altributes the ice accumulation to 
great uplifts of the land bringing a snowy climate throughout the year. 
This view. howe\<;i'. will I'.xplain how the Fa'i-oe islands. Iceland and 
(jlreenlan<l. may liaxc received their largely European floras: I'orif the 
