THE ORIGIN OF MOUNTAINS. 
73 
compression with folding. Whenever we find a fold 
we may be sure that, when formed, it was deep 
down, far below the surface. 
In fact folds and fractures are the two means by 
which the interior strains adjust themselves. They 
replace one another, and in the marvellously folded 
districts of the Alps faults are comparatively few, 
though it must not be supposed that they do not 
occur. The nature of the rock has little influence on 
the great primary folds, but the character of the 
minor secondary folds depends much upon it. 
Fig. 15 represents a piece of contorted mica 
schist, and it will be seen that the folds are a minia- 
ture of those to which on a great scale our mountains 
are due. 
Many of the following figures give an idea of 
the remarkable folds and crumpling which the strata 
have undergone, so much so that they have been 
compared to a handful of ribbons thrown on to the 
ground. 
It is obvious that before strata could be thrown 
into contortions such as these, they must have been 
subjected to tremendous pressure. They have conse- 
quently been much altered, and the fossils have been 
compressed, contorted, crushed, ground, and partly, 
or in many cases entirely, obliterated. 
