78 
SCENERY OF SWITZERLAND. 
first explained by Lory. Fig. 25 gives a section 
across the Mont Blanc range. 
A similar fan-shaped structure occurs in the 
St. Gotthard (Fig. 26), the Grimsel, the Silvretta, etc., 
and may indeed be said to occur in all the northern 
Crystalline Massives of the Alps, but not in the Ticino, 
Adula, etc. It has also been found in the Pyrenees, 
in Pennsylvania, and some other mountain ranges.* 
Figs. 94 and 95, showing the folds assumed by 
layers of clay, sand, etc., in two of Mr. Cadell’s ex- 
periments, compared with the section of the Mont Blanc 
Massif given in Fig. 25 (vol. i. p. 94), or that of the St. 
Gotthard in Fig. 26 (vol. 1. p. 95), show how the struc- 
ture of these mountain ranges may have originated. 
In attempting to understand the structure of the 
Central Massives, the first problem which confronts 
us IS the true nature of the Crystalline rocks. They 
were long regarded as intrusive plutonic rocks, which 
* Favre, Rich. Geol., in. 
