central MASSIVES. 
75 
regards as metamorphosed sedimentary rocks, and 
he refers to places where the one passes imper- 
ceptibly into the other. But on these points there 
are still great differences of opinion. 
On a larger scale the sections show repeated suc- 
cessions of similar rocks, and the more they are ex- 
amined the more complicated do they appear. 
In the Aar section we find Granite repeated at 
least nine times, Gneiss-Granite ten times. Eyed- 
gneiss. Mica Gneiss, and Grey Gneiss several times. 
In the Reuss Valley the Granite and Crystalline 
schists alternate some twenty times in a distance of 
4 km. The Urseren fold is itself double, or perhaps 
even more complicated. These changes may in some 
cases be due to faults and overthrusts, but in general 
appear to indicate folds. Baltzer considers that the 
Aar massif comprises at least six.* 
The following figure (Fig. 93) representing the 
section of the St. Gotthard Tunnel, shows this com- 
plexity very clearly. 
The existence of “bosses,” such as the great 
“massives,” would naturally follow from the general 
view of the Swiss Alps, which has been given above. 
It would be most improbable in any case, that we 
* Baltzer, Beitr. z, Geol. K. d. Schw.f L. xxiv. 
