150 
by ancient glaciers, wHcli once extended far beyond tbeir 
actual limits. That they did so extend is in several instances 
well ascertained and proved ; that they did, in the manner 
suggested, plough out the valleys and lakes is a proposition 
which cannot be accepted, until we possess more knowledge 
than has yet been attained, regarding the resistance offered 
by ice to a crushing force, its tensile strength, the measure 
of its resistance to shearing, and other data required for 
a just estimate of the problem. At present it would appear 
that under a column of its own substance 1,000 feet high, 
ice would not retain its solidity; if so, it could not propagate 
a greater pressure in any direction. This question of the 
excavating effect of glaciers is distinctly a mechanical prob- 
lem, requiring a knowledge of certain data, and till these 
are supplied, calculations and conjectures are equally vain." 
In reviewing the points in Professor Phillip's address, 
with the somewhat presumptuous intention of criticising his 
conclusions, I shall offer no apology for beginning at the 
beginning, though, in so doing I shall have to state facts 
perfectly familiar to all my hearers. 
Let me, then, first of all, call your attention to the 
change in volume suffered by water, cooled from the boil- 
ing point to 12° F., passing into ice at 32° F. The 
volume decreases, always at a decreasing rate, till it attains 
its minimum value at 4° C, or 39° F., then slowly, increases. 
By carefully cooling water so as to avoid agitation, 
the temperature may be reduced to 9° C. without its freez- 
ing, and through this range of temperature the anoma- 
lous expansion continues. But if the water be allowed 
to freeze, then at the moment of the change of con- 
dition, an enormous increase of volume takes place. 
There is thus, apparently, a perfectly sudden change from 
the mobility of a liquid, which enables it readily to assume 
the form of the vessel in which it is contained, to the 
