Glacial History of Western Europe. 467 
be 1,200,000 years, and of the Miocene 1,400,000 years. To 
estimate the total vertical thickness of rock which has been removed 
from the Alps by denudation is far from easy, but I think 14,000 feet 
would be a liberal allowance, of which about one-seventh is assigned 
to the Ice Age. But during that age, according to a curve given by 
Penck and Briickner, the temperature was below its present amount 
for rather less than half (47) the time. Hence it follows that, since 
the sculpture of the Alps must have begun at least as far back as the 
Miocene period, one-seventh of the work has been done by ice in not 
quite one-fifteenth of the time, or its action must be very potent. 
Such data as are at our command make it probable that a Norway 
glacier at the present day lowers its basin by only about 
80 millimetres in 1000 years, a Greenland glacier may remove some 
421 millimetres in the same time, while the Vatnajokul in Iceland 
attains to 647 millimetres. If Alpine glaciers had been as effective 
as the last-named, they would not have removed, during their 
188,000 years of occupation of the Alpine valleys, more than 
121°6 metres, or just over 3897 feet; and as this is not half the 
amount demanded by the more moderate advocates of erosion, we 
must either ascribe an abnormal activity to the vanished Alpine 
glaciers, or admit that water was much more effective as an excavator. 
We must not forget that glaciers cannot have been important agents 
in the sculpture of the Alps during more than part of Pleistocene 
times. That sculpture probably began in the Oligocene period ; for 
rather early in the next one the great masses of conglomerate, called 
Nagelfluh, show that powerful rivers had already carved for themselves 
valleys corresponding generally with and nearly as deep as those still 
in existence. Temperature during much of the Miocene period was 
not less than 12° F. above its present average. This would place 
the snow-line at about 12,000 feet.! In that case, if we assume the 
altitudes unchanged, not a snow-field would be left between the 
Simplon and the Maloja, the glaciers of the Pennines would shrivel 
into insignificance, Monte Rosa would exchange its drapery of ice for 
little more than a tippet of frozen snow. As the temperature fell 
the white robes would steal down the mountain-sides, the glaciers 
grow, the torrents be swollen during all the warmer months, and the 
work of sculpture increase in activity. Yet with a temperature even 
6° higher than it now is, as it might well be at the beginning of the 
Pliocene period, the snow-line would be at 10,000 feet ; numbers of 
glaciers would have disappeared, and those around the J ungfrau and 
the Finster Aarhorn would be hardly more important than™ they now 
are in the Western Oberland. 
But denudation would begin so soon as the ground rose above the 
sea. Water, which cannot run off the sand exposed by the retreating 
tide without carving a miniature system of valleys, would never leave 
the nascent range intact. The Miocene Alps, even before a patch of 
1 T take the fall of temperature for a rise in altitude as 1° F. for 300 feet, or, 
when the differences in the latter are large, 3° per 1000 feet. These estimates will, 
I think, be sufficiently accurate. The ficures given by Hann (see for a discussion of 
the question, Report of Brit. Assoc., 1909, p- 93) work out to 1° F’. for each 318 feet 
of ascent (up to about 10,000 feet). 
