38 
SCENERY OF SWITZERI^AND. 
corals, and m other districts fragments of Belemnites; 
such pebbles cannot belong to the Tertiary period,' 
Belemnites being then already extinct. 
It is remarkable that many of the pebbles of the 
Nagelflue seem to be exotic, that is to say, they do 
not belong to rocks found in the neighbouring 
mountains. We find scarcely any blocks or pebbles 
of the Granite, Gneiss, and Crystalline schists which 
now form the central mountain range of the Alps. 
Amphibolite, Serpentine, Verrucano, and other rocks 
which we should have expected to meet with, seem 
to be entirely absent. At the time of the Nagelflue, 
however, these rocks were covered to a great depth 
by the sedimentary strata. Some of the pebbles do 
not agree with any rock now found in or ncoar the Alps. 
It has, however, been suggested that some of these 
may really have been derived from the Alpine rocks, 
but before the enormous pressure had brought them 
into their present condition. The Nagelflue is 
evidently a gi avel formation — an enormous cone 
deposited at the northern edge of the Oligocene and 
Miocene Alps. 
The sources of certain pebbles can, however, be 
ascertained with great probability, and Friih con- 
cludes that the rivers came from the S. and S.E. 
Hie watershed was then further south than it is at 
