276 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
destroy them; and their rugged remnants are highly significant of 
what a glacier can do. 
Rocky Knobs in Glaciated Areas .— On thus generalizing the 
lesson of the Rhue, it is seen that just before the complete oblitera¬ 
tion of the spurs some of their remnant knobs may be isolated from 
the uplands whence these preglacial spurs descended. It is out of 
the question to regard the ruggedness of such knobs as an indication 
of small change from their preglacial form, as has been done by 
some observers. The ruggedness is really an indication of the 
manner in which a glacier reduces a larger mass to smaller dimen¬ 
sions, by plucking on the down-stream side as well as by scouring 
on the up-stream side. It is possible that knobs in other glaciated 
valleys than that of the Rhue may be of this origin; they should 
then be regarded not as standing almost unchanged and testifying 
to the incapacity of glacial erosion, but as surviving remnants of 
much larger masses, standing, like monadnocks above a peneplain, 
as monuments to the departed greater forms. The two knobs at 
Sion (Sitten) and the Maladeires, all detached from Mont d’Orge 
in the upper valley of the Rhone, the hills of Bellinzona in 
the valley of the Ticino, the rocks of Salzburg where the Sal- 
zacli emerges from the Alps, and even the Borromeo islands in 
Lake Maggiore, may perhaps be thus interpreted. Rugged as these 
knobs may be on the down-stream side, it would be an unreasonable 
contradiction of the conclusions based on observations of many 
kinds to maintain that their ruggedness was of preglacial origin. 
The ice stream from the Cantal at one time expanded sufficiently 
to flood the uplands bordering the valley of the Rhue, 1 where it 
produced changes of a most significant kind. The neighboring 
unglaciated uplands are of systematic form ; broad, smoothly arched 
masses rise, round-shouldered, between the narrow Valleys that are 
incised beneath them; the uplands are as a rule deeply soil-covered, 
and bare ledges prevail only on the stronger slopes of the young 
valleys that have been eroded since the peneplain was raised to its 
present upland estate. But within the glaciated area near the 
Rhue, the broadly rounded forms of the uplands are replaced by a 
succession of most irregular rocky knobs, from which the preglacial 
soils have been well scoured away, as in Fig. 2. This seems to be 
a form most appropriate to glacial action on a surface that had been 
1 According to Boule (’96), the glaciation of the uplands and of the valleys was sepa¬ 
rated by an interglacial epoch, but I did not have occasion to inquire particularly into 
this aspect of the problem. 
