114 The American Geologist. February, 1894 
portion of eastern North America, the Arctic archipelago, and 
Greenland, showing the limits of the ice-sheet and glacial 
drift and the derivation of the Ohio boulders from Canada, 
Divisions of the Pleistocene Period. 
Excellent suites of specimens of the rock formations and 
fossils of the United States, exhibited in the Government 
building by the U. S. Geological Survey, comprised samples 
of glaciated stones, of the boulder-clay or till, of loam from 
the Columbia formation in Washington, 1). ('., and of the 
Mississippi valley loess. On an accompanying placard it was 
stated that the Pleistocene period included the following di- 
visions: "I. Transition epoch. II. Earlier Glacial epoch. 
III. Chief interglacial epoch. [V. Later Glacial epoch. Y. 
Champlain epoch. VI. Terrace epoch." 
Concerning this subdivision, it may be remarked that the 
first or Transition epoch was probably characterized by a gen- 
eral epeirogenic uplift of the region which became ice-envel- 
oped. The slow r uplifting to such altitude as to give a cold 
climate and snowfall during nearly all the year, leading to the 
lee accumulation, may have comprised a longer time than 
the ensuing epochs of glaciation and departure of the ice. 
with the deposition of its drift and the stream channelling 
and terracing of the glacial flood plains. Whether the stages 
of glacial retreat and readvance during the Ice age should be 
regarded as marking epochs or subordinate episodes of the 
Pleistocene period seems at present to be undetermined. 
Some of the most recent studies of our drift are found to sup- 
port the view that the glaciation was continuous, moderate 
fluctuations of the ice-front being thought to be sufficient to 
account for the forest beds between deposits of till and for 
eroded drift valleys covered by subsequent advances of the 
ice-sheet. 
[Models and Relief Macs illustrating Pleistocene History. 
About twenty models of districts and localities in the 
United States, possessing features of special geological inter- 
est, were exhibited by the IT. S. Geological Survey. Among 
these we noted, as illustrative of Pleistocene geology, the series 
of models of northeastern Iowa prepared under the direction 
