MORAINES OF RECESSION 443 
Again, discussing glacial motion more broadly, Professor 
Chamberlin says, referring to Greenland: 
No average measurements, nor anything approaching to average meas- 
urements, have been made. The high rates of movement of the Jacobshaven 
glacier, as given by Helland, and of the Great Karajak glacier, as given by 
Drygalski, and other similar measurements, are not at all questioned, but 
these are quite exceptional, and almost as far as possible from being repre- 
sentative. They exhibit extraordinary movements through deep constricted 
straits, where the ice is forced by the vast accumulations of great areas in 
the rear, and where the warm season appears to exert its earliest and great- 
est effects. The amount of ice discharged in the form of bergs from these 
two glaciers is very much greater than from any other known points on the 
ice-front of Greenland. It is perfectly obvious that the average border of 
the Greenland ice-sheet does not move at a rate even distantly approximat- 
ing that of these two straits. If it did so, the whole coast of Greenland must 
be overwhelmed almost immediately, because the competency of the summer 
heat of that region to hold back the edge of the ice by melting is very 
slight. Drygalski estimated the annual surface melting at seven feet. Even 
this is much greater than the annual surface melting of the Inglefield Gulf 
region, judged by that of 1894. While estimates are few, and even these 
may need much qualification, it is nevertheless certain that the average 
movement of that portion of the border of the Greenland ice-cap which lies 
upon the land is extremely small. Of that portion which ends in the sea 
only a small fraction has a high rate of motion, as is shown by the lack of 
activity in the discharge of icebergs. When it is considered that the land 
border is very much greater than the sea border, and that of the sea border 
a portion has a relatively slow movement, it will be evident that the average 
rate of movement for the border of the great ice-sheet of Greenland cannot 
be high; and the average rate of this border is the nearest available 
analogue to the border movement of the still more extended periphery of 
the ancient American or Laurentide glacier.* 
There can hardly be a doubt of the great value of the Green- 
land observations in their bearing on the conditions attending 
the Laurentide glacier that invaded the United States. It will 
be observed that most of the measured rates of motion reported 
by Peary, Chamberlin, and Salisbury are of ice tongues flowing 
out a few miles from the main cap down valleys generally 
*The Glacial Lake Agassiz, by WARREN UPHAM. Monograph XXV, U. S. 
Geol. Survey, 1896. Topic entitled ‘Alternative Interpretations,’ by T. C. CHAM- 
BERLIN, pp. 248-249. 
