PROGRESSION OF GLACIERS. 
279 
3t ils produisent ensuite de l’eau a zdro qui tombe 
dans le glacier refroidi et fendille. Cette eau s’y 
congele a 1 instant, en laissant degager de la clia- 
leur qui tend a ramener le glacier a zdro; et 
le phdnomene se continue jusqu’a ce que la 
masse entiere du glacier refroidi soit ramend a la 
temperature de zdro.”* 
But where direct observations are still so scan- 
ty, and the interpretations of the facts so con- 
flicting, it is the part of wisdom to be circum- 
spect in forming opinions. This much, how- 
ever, I believe to be already settled: that any 
theory which ascribes the very complicated phe- 
nomena of the glacier to one cause must be de- 
fective and one-sided. It seems to me most 
*“ During' the winter, the temperature at the surface of 
the glacier sinks a great many degrees below 32° Fahrenheit, 
and this low temperature penetrates, though at a gradually de- 
creasing rate, into the interior of the mass. The glacier be- 
comes fissured in consequence of the contraction resulting from 
this cooling process. The cracks remain open at first, and con- 
tribute to lower the temperature of the glacier by favoring 
the introduction of the cold air from without ; but in the spring, 
when the rays of the sun raise the temperature of the snow cov- 
ering the glacier, they first bring it back to 32° Fahrenheit, and 
presently produce water at 32°, which falls into the chilled 
and fissured mass of the glacier. There this water is instantly 
frozen, releasing heat which tends to bring back the glacier 
to the temperature of 32°; and this process continues till the 
entire mass of the cooled glacier returns to the temperaturo 
of 32° .” 
