CHAPTER XIII. 
MOUNTAINS AND FJELDS. 
Ir may have been observed that in the details given in 
regard to the geographical distribution of different kinds 
of forest trees in Norway, mention is made chiefly of 
latitude, but the fact: that such distribution is affected by’ 
altitude as well as by latitude must not be ignored. There 
is a co-relation between the two in so far as temperature is 
concerned ; and it is mainly in relation to temperature 
that the relation of altitude in different localities at which 
different trees grow becomes of importance in discussious 
connected with this fact. But the difference observable 
is not related to this exclusively. The soil is generally. 
different in the plain, and even at the base of a moun- 
tain, from what it is on the sides, and on the summit of 
that mountain; and there is also a difference in the 
atmospheric pressure at a high altitude, and at the level 
of the sea, and at ail intermediate altitudes, which differ- 
ence of pressure may not be without effect on the geo- 
graphical distribution of trees. 
To the establishment and acceptance of this as a fact, 
‘it is not necessary that we should know how it is that 
it produces the effect; it is a fact determined by observa- 
ae ; and it may be seen on the ocean as well as on dry 
and. 
‘The ocean, as well as the land,’ writes Balfour, ‘ possesses 
its vegetable forms, which are of a peculiar kind, and- exist 
under different conditions of pressure, of surrounding 
medium, and of light. Some sea-weeds, Harvey remarks, 
are cosmopolitan or pelagic, as species of ulva and enterce 
morpha, which are equally abundant in high northern and 
