Slialer.] 
166 
[March 16, 
in the position of their termini at varying intervals that may be 
scores of years apart. 
3. While glaciers are very delicate indices of rainfall, this ele- 
ment in their development is so complicated by other actions, 
that any study of this feature must rest upon observations above 
the line of the upper seracs, i. e. above the lower line of perpetual 
snow. 
4. That a careful comparative study of the neve districts may 
afford reliable data for the determination of the average rain- 
fall in various periods in the past, and may give some clue to the 
age of the periods of great or scanty snow-fall that are now pro- 
ducing advances and recessions at the end of the glacier. 
The advance and recession of the great glaciers of the last ice 
epoch have some light thrown upon them by the changes in the 
existing glaciers of our mountain valleys. It is clear that an an- 
nual difference of an inch or two of rainfall would profoundly affect 
the extension of the ice of these sheets. As the principal melting 
was at the front or terminus of the ice, nearly all the ice over a 
large field would have to be transferred to the front to be melted; 
allowing that the melting front was a mile in width and the gath- 
ering ground a hundred miles in width, a gain in thickness of the 
ice of ten feet would mean a gain at the front of one thousand 
feet, which would necessarily bring about a great advance of the 
face of the glacier. Supposing the forward movement to be one 
foot in a day, an increase of an inch a year in the rainfall would 
deepen the ice by the amount of over one thousand feet, and 
bring about a great extension of the ice front. We thus see that 
without any profound changes of climate, very extensive retreats 
and advances of the ice might be brought about. 
Considering the importance of further study upon the region 
oh the neve, the terra incognita of the subject, I feel justified in sug- 
gesting the possible use of a cheap boring machine, of the dia- 
mond drill fashion, which might be advantageously employed 
upon the surface of these fields, to ascertain their depth. Such 
machines, the cutting tools armed with steel points, moved by 
hand power, are now in use for explorations of a preliminary sort 
in mining. It may be necessary to force a small amount of steam 
down the tube to effect the clearance of the ice from the cutting 
