L6 Tne American Geologist. January, 1896 
L893. On New England and the Upper Mississippi basin in the Glacial 
period. Amer. .lour. Sci., (3), vol. 16, pp. 327-330. 
1894. Observations on the derivation and homologies of some articu- 
lates. Ibid., vol. 17. pp. 325 329. 
is!):.. Manual of geology, 4thedition, L057 pp., 8vo, New Fork. 
PHYSICAL CONDITIONS OF THE FLOW OF 
GLACIERS. 
By Waeken Upham, St. Paul, Minn. 
I Plate n.i 
Historical Introduction. 
Chiefly to Louis Agassiz, during the years L838 to 1847, 
following lines of study begun by Venetz, Charpentier, 
Guyot. and others, we owe the geological application of the 
observations of the work of existing glaciers in the Alps to 
explain, first, the extension of the Alpine Pleistocene glacial 
drift across the great valley of Switzerland to the Jura 
mountain range, and. second, the origin and methods of for- 
mation of the Pleistocene drift deposits in the British Isles, 
northern Europe, and the north half of North America. 
On the other hand, we are chiefly indebted for the most 
important early discoveries and descriptions of the physical 
structure of glaciers to .lames David Forbes, during the 
years 1 S4 1 to 1X59. working partly in association with 
Agassiz, but mostly separate and independent, on account of 
their conflicting claims to certain discoveries, and their 
different interpretations of the veined structure and methods 
of flow of glaciers. Guyot and Agassiz considered the laini 
nation of the glacier ice in blue and white bands to be due to 
the stratification of the high snowfields by the deposition of 
successive snow storms and by the alternations of winter and 
summer; but Forbes in 1842, and Tyndall in L859, showed by 
definite and crucial observations and reasoning that this 
veined or ribboned structure results from the movement of 
the ice in its unequal onward flow, where it is subjected to 
great pressure, with shearing of the interlaminated blue and 
white ice. 
English and American glacialists and physicists, in their 
studies and discussions of the motion of glaciers, have de- 
voted most of their attention to the veined structure, to the 
crevasses, and to the regelation of the ice from a crevassed to 
