THE OUTER- ALPS. 
59 
figure, tire layers of gravel dip in towards the hill in 
the direction of the Scheidegg. They were in fact 
originally continued so as to form a great arch, the 
summit of which was (Fig. 85) approximately over 
the Bay of KUssnacht, and the north-west side im- 
mediately on the other side of the bay, where the 
strata are nearly horizontal, rising however almost 
immediately into another arch, which forms the 
Rooterberg. We must therefore allow for another 
long period, during which the summit and north-west 
limit of the arch were destroyed and removed. 
6. The actual pebbles themselves have been care- 
fully studied by Dr. FrUh, whose Memoir has been 
referred to in the previous chapter, and I will here 
only refer briefly to three points. 
1. If the central mountain ranges had been as 
they now are, much of the gravel must have been 
derived from the Jurassic and Crystalline rocks, but 
these are comparatively scarce, no doubt because at 
the time the gravel was being carried down the 
central rocks now exposed were covered by thick 
beds of the younger Secondary strata which have 
now disappeared. 
2. Some of the pebbles are fragments of rocks 
as yet only found on the Italian side of the cential 
ridge. They cannot of course have been brought 
