Glacier Work.— Scott. 227 
Since it is reasonable to presume that motion is by no 
means confined to the upper or surface layers of a glacier, 
but has to do with the whole thickness, it is here proposed to 
consider the mass as divided primarily into two parts. 
1. An upper zone of fracture, or crevasses. 
2. A lower zone of constant plasticity. * 
The portion of a glacier above zvhich the ice is under less 
zveight than its yielding resistance is in the zone of fracture 
or crevasses. 
The first point to be considered in connection with this zone 
rests upon some interesting experiments upon ice blocks by 
Col. William Ludlow (1880-81) t, A. Fruhling (1885) $, 
C. W. Beach, A. M. Mann, and H. E. Reeves (1895) §. 
The results of these experiments as far a? recorded show 
that the maximum yielding resistance of pure ice a few 
degrees below the freezing point, to compressive stress, is 
under 300 pounds per square inch. It thus appears that 
crevasses or cracks of any sort cannot exist below a limited 
depth. To determine this depth, it simply remains to cal- 
culate the height of a column of ice one square inch in 
cross section which shall have a weight of three hundred 
pounds and the result shows this to be not over 750 feet. It 
should be said here that all these experiments show a wide 
range of results, largely due, doubtless, to variable qual- 
ity of ice and temperature and rate of deformation ; so that 
an average rather than a maximum value, as above cited, 
would reduce the depth limit to about one-half the value 
given, or 300 feet, approximately. Another point to be con- 
sidered, is the question as to whether the 'ce blocks tested 
were of the proper dimensions to give the correct results for 
larger masses of this material. The specimens used by all 
of the experimenters, so far as is apparent to the writer, were 
cubes of various sizes. 
*This idea, and others also, embodied in this paper, have originated 
primarily from a study of "Principles of N. A. Pre-Camtarian Geology," 
and "Metamorphism and .Rock Flowage," by Prof. C. R. Van Hise, 
Rep. U. S. Geol. Survey, 1894-95; Bull. Geol. Soc. of America. Vol. 9, pp. 
2G9-32S. 
t "Observations on the Crushing Strength of Ice." Proceedings of 
the Engineers' Club of Phil. 18S4, Vol. IV, p. 93. 
JZeitschrift des Vereines deutschen Ingenieure. May 9, 1SS5, p. 357. 
§Digest of Physical Tests, 189(5-97. 
