MOUNTAINS AND THEIR ORIGIN. 105 
Jura. But though this is the 
prevailing character of the 
range, there are many instan- 
ces even here where an une- 
qual pressure has caused a 
rent at right angles with the general direction of 
the upheaval ; and one may trace the action of 
this unequal pressure, from the unbroken arch, 
where it has simply lifted the surface into a 
dome, to the granite crest, where the melted rock 
has forced its way out and crystallized between 
the broken beds that rest against its slopes. 
In other instances, the upper beds alone may 
nave been cracked, while the continuity of the 
lower ones remains unbroken. In this case we 
have a longitudinal valley on the top of a moun- 
tain-range, lying between the two sides of the 
broken arch (as in 
Figured). Suppose, 
now, that there are 
also transverse cracks 
across such a longitu- 
dinal split, we have 
then a longitudinal valley with transverse valleys 
opening into it. There are many instances of 
this in the Alleghanies and in the Jura. Some- 
times such transverse valleys are cut straight 
across, so that their openings face each other ; 
but often the cracks have taken place at different 
Fig. 4. 
Fig. 3. 
