CENTRAL MASSIVES. 
77 
should have a simple succession of ridges extending 
the whole length of the mountains, and especially so 
in a curved chain, such as the Alps. Moreover, we 
find as a matter of fact, that folds rarely extend the 
whole length of a range. In the Jura, for instance, 
which extends over 300 km., the folds have lengths 
of 12, 27, 28, 31, 45, 14, 51. 92, 48, and in one 
case 162 km. respectively. The length, I may add, 
has no relation to the height. Thurmann calculated 
that for the whole Jura there are no less than 
160 folds, though there are never more than 12 in 
any one cross section. 
As a rule the strata on the northern line of the 
Central Massives are inclined at a high angle, and 
indeed are in places perpendicular. This may be 
said to be the rule in the centre, while they are less 
steeply inclined at the sides. The inclination, how- 
ever, instead of being, as might at first sight have 
been expected, away from the centre, trend towards 
it. Indeed, so extreme has been the pressure that 
the central ranges have been squeezed into a fan- 
shaped structure, long ago noticed by Saussure, who 
described them as throwing themselves against the 
mountain, or like a crowd rising on tiptoes and lean- 
ing over in the effort to see over one another. The 
arrangement was also well described by Studer, but 
