446 FRANK BURSLEY TAYLOR 
There are some writers who make the whole period of gla- 
ciation very short. Mr. Upham believes that Lake Agassiz 
‘‘endured only a thousand years or less,’ and he allows ‘“‘only a 
few (perhaps four or five) thousand years” for the entire glacial 
retreat, including the whole Champlain period of submergence 
and most of the later reélevation of the land.t But it seems to 
me that both fact and theory as they stand today clearly incline 
toward a long rather than a short time.” 
TRANSPORTATION AND DEPOSITION OF ENGLACIAL DRIFT. 
If we turn to the best available evidence bearing on the 
manner and rate of drift transportation by the ice-sheet we meet 
with facts tending to the same general conclusion, viz., that 
the building of the moraines was a very slow process. ‘The rate 
of glacial motion is necessarily a function of the rate of drift 
deposition. If it is sufficiently clear that the ice motion was very 
slow we have that much gained towards a determination of the 
probable rate of moraine building. The other function is the 
drift load, and we have now to consider what evidence can be 
brought to bear upon it and also what theoretical considerations 
indicate as the probable truth. 
Here again the Greenland ice-sheet is the closest available 
analogue and the significance of its indications relating to drift 
load and deposition are well set forth by Professor Chamberlin. 
On these points he writes as follows: 
That considerable débris is borne in the basal portion of the ice is not 
questioned ; indeed, the term, “‘englacial drift’”’ was proposed by the present 
writer in recognition of its importance. Our best evidence of the amount 
™ View of the Ice age as two Epochs, the Glacial and Champlain.” Proc. A. A. 
A.S., Vol. XLIV, 1895, p. 144. Also Am. Geol., XVI, August 1895, p. 107. For 
duration of Lake Agassiz see also “Glacial Lake Agassiz,” by WARREN UPHAM. 
Monograph, pp. 241-242. 
2 Instudying the history of such a glacier as the Muir of Alaska with its relatively 
rapid advances and retreats (“Glacier Bay and its Glaciers,” by H. F. REID, 16th Ann, 
Rept. U. S. Geol. Survey ; map opposite page 454), and like many of those that calve 
icebergs in Greenland, it must be remembered that the conditions of their motion are 
not at all like those of an ice-sheet and that they do not furnish safe criteria for inter- 
preting ice-sheet motion. 
