Perry.] 90 _ [February 28, 
essary to mention in this place, since a careful study of the matter is 
sure to bring them to mind, may serve to show that the motion of 
the icy mass is almost a matter of necessity. One may also surmise 
from these hasty statements the nature of some of the many condi- 
tions and agencies concerned in glacial motion, which cannot be 
given in detail, though a knowledge of them be requisite to a full 
understanding of the subject. 
Professor Dana, however, appears to look at the matter dalle aie: 
if not in an entirely diverse light. He says, and this seems to be 
his main statement in reference to the point, “the glacier owes its 
power of movement to the facility with which it breaks and mends 
itself’! That ice breaks under certain circumstances, and in break- 
ing, or as broken, may more readily pass over, or move around given 
obstacles, is of course perfectly evident; but what causal relation 
exists between its mending and its motion, or what motive power 
inheres in the process, is not so plain. Applying the same phrase- 
ology to water, of course with due allowance for admitted differences, 
we fail to find in the second term any meaning whatever, so far as 
tendency to motion is concerned. But, waiving the further examina- 
tion of this point, one may reasonably ask, whether there be not far 
too much efficiency ascribed to this supposed agency. Breaking and 
mending, while they should not be overlooked, are, after all that may 
be said, little more than concomitants in glacier-motion. All the 
breaking and mending in the world, by flere alone and if there 
be nothing besides, would not necessarily carry the mass of ice for- 
ward in the least. 
Meanwhile there are various conditions and agencies, in connec- 
tion with which, as we have seen, movement would actually occur. 
Great cold prevailing on the northern limits of the ice-sheet, and 
serving as a barrier to its motion in that direction, there being at the 
same time a partial melting of its southern face, the waters from the 
wasting snows on its surface percolating the icy mass, there also 
being contractions and expansions consequent upon alterations in 
the temperature; all these being connected with the gravitating force 
1 Paper cited, p. 50. 
2 A remark of Professor Agassiz, who is perfectly familiar with the phenomena 
of existing glaciers, suggests the little prominence which should be given to the 
agency in question. “ Breaking and mending,” he lately said to me in conyersa- 
tion, “‘only take place where glaciers form cascades, or rapids as it were, over 
greatly uneven ground.” 
