112 
on the ground, but a one-sided, telling at a glance 
ind th 
the direction of the . On the wind-swept sides of the 
mountains the timber he not reach oe far as high and in many 
places there is no timber at all. In the Abajo Mountains of 
southwestern Utah, for instance, ce is no timber above the 
semi-arid cedar-pifion belt of the foot-hills 
5. Deep snow. As the desiccating ane lower the altitude 
on the wind-swept regions, so does the snow in the heads of the 
valleys, not only by shortening the growing season, but also 
by smothering the tree vegetation. Herbs and low shrubs can 
stand to be covered over by snow much better than trees, for 
their growing season does not begin before the snow is practically 
the ground. While the tops of the trees may be above the 
snow and exposed to the summer heat much before the snow- 
covered roots and lower branches have been melted, the lower 
portion of the tree is cut off from the air while the upper portion 
is already in vital activity. It is easier to distinguish trees 
stunted ae the action of wind than those stunted by the smother- 
gs n the former the lower branches are enormously 
peeeen cae with the upper, while in the latter the lower 
branches are dead or covered by fungi or their mycelium. The 
usual condition in the Rockies is that wherever there is a large 
valley head where the snow has chance to lodge, this is always 
devoid of trees, except in places of higher ground where the 
snow drifts have not been so 
6. Form of precipitation. In high altitudes it is too rare to 
hold much moisture and the rain falls at the least lowering of the 
temperature. The rain falls, therefore, in the form of mists or in 
light and fine showers which only wet the surface. Nowhere in 
the Rockies is the moisture very great. In the foot-hill region 
and on the surrounding plains, the temperature in the summer is 
too high to allow any precipitation. These zones are also arid. 
It is at middle elevation that the precipitation is the greatest. 
e air here is dense enough to hold more moisture and the 
temperature low enough to aes precipitatio: 
7. Large mountain masses. In the Swiss ie observations 
have also been made that in regions of large mountain masses 
