io6 
SCENERY OF SWITZERLAND. 
The “cap” was in fact formed of Jurassic strata, 
conclusively demonstrating that the Secondary rocks 
once extended continuously over the massif; and, to 
judge from their thickness elsewhere, the amount of 
the Secondary rocks denuded can hardly be less 
than 3000 metres, to which a substantial addition 
must be made, as a considerable thickness of the 
crystalline rocks has also been removed. 
Whether the same can be said of the older Ter- 
tiary strata is not so clear, but as they terminate 
along the north side of the Mont Blanc massif in a 
great escarpment, it is certain that they must at any- 
rate have extended far beyond their present limits. 
South of the Alps the cretaceous and nummulitic 
strata reappear in the neighbourhood of Varese and 
Turin. 
At anyrate, however the Secondary strata formed 
a great arch over the Buet, dipping down into a 
compressed synclinal fold, which was the determin- 
ing cause of the valley of Chamouni, and then 
(Figs. 104, 105) rose up into a great arch over the 
central Mont Blanc range. Mont Blanc therefore 
was once covered by from 10,000 to 15,000 feet of 
strata, which have been entirely removed. 
The lapse of time thus indicated must have been 
enormous. It has been calculated that the general 
