MOUNTAINS AND THEIR ORIGIN. 107 
:iglH through a transverse crack, flowing north- 
ward between walls fourteen thousand feet high, 
till it enters the Lake of Geneva, through which 
it passes, issuing at the other end, where it takes 
a southern direction. For a long time moun- 
tains were supposed to be the limitations of rh. 
ers, and old maps represent them always as flow- 
ing along the valleys without ever passing througt 
the mountain-chains that divide them ; but geol- 
ogy is fast correcting the errors of geography, 
and a map which represents merely the external 
features of a country, without reference to their 
structural relations, is no longer of any scientific 
value. 
It is not, however, by rents in mountain-chains 
alone, or by depressions between them, that val- 
leys are produced ; they are often due to the un- 
equal hardness of the beds raised, and to their 
greater or less liability to he worn away and dis- 
integrated by the action of the rains. This ine- 
quality in the hardness of the rocks forming a 
mountain-range, not only adds very much to the 
picturesqueness of outline, but also renders the 
landscape more varied through the greater or less 
fertility of the soil. On the hard rocks, where 
little soil can gather, there are only pines, or a 
low, dwarfed growth ; but on the rocks of softer 
materials, more easily acted upon by the rain, a 
richer soil gathers, and there, in the midst of 
