The Pleistocene and Glacial Flora. 
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Pleistocene Flora. A) BERTRE: 
as: 1252188 
BI a a: 
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Quercus macrocarpa Michx. . . .» 2... -H 
> acuminata Michx. (= Q. Muhlenbergii 
Engelm.) . ee En — _ 
Robinia pseudacacia L. . nn ee wi 
BIN DA ee + en FR 
Taxus canadensis Marsh. en u Fr 
Thuja occidentalis L.. ee a ve 
Tilia americana L. 4 Er ee 
Typha latifolia L. . hr > Pi 
Ulmus americana L. . . E er u 
» racemosa Thomas + a 
Vaccinium uliginosum L. RE 
Vallisneria spiralis L.. ar eo en 
Zostera marina L.. | + 
Totals . ERBE 12:26 
3. The Glacial Flora. 
The Wisconsin stage, and last one, is the most conspicuous and best 
known of all, and its sheets of till and drift are far thicker than those of the 
other glacial stages. Especially conspicuous is the great terminal moraine, 
which has been traced across the continent. 
The final retreat of the ice, of which in New England there is no clear 
evidence of more than one glacial stage, was by slow steps with many halts. 
In the central West are preserved many lines of moraine, with kettle-holes, 
kames and drumlins which mark successive pauses in the retreat. An inter- 
esting episode of later glacial times was the formation in Minnesota and Ma- 
nitoba of a great body of fresh water, Lake Agassiz, which was 700 miles 
long from north to south. In the Great Basin, the Pleistocene was a time of 
far less arid climate than at present. In the eastern part of the Basin was 
established the great Lake Bonneville, which had an outlet north into Snake 
River. 
If we consider these facts proved, then the only glaciation which could 
materially affect the distribution of our boreal societies is that of the last, or 
Wisconsin epoch. Through the work of Chamberlain, Leverett, Salis- 
bury, Upham and others, the limits of this ice invasion have been definitely 
mapped. According to Chamberlain, the climatic conditions prevailing about 
the margin were intermediate between those of Greenland and Alaska at the 
