ocT., 1899. ] SLOPE EXPOSURE. 47 
the sun, which became deep red like the fall moon and then disappeared. 
At 5 o'clock the smoke began to settle back, as it always did when the 
chill of the evening came on, and the sun reappeared, to set as usual 
behind the dark outlines of the distant mountains. 
Fires on the south, in the valley of the McCloud, cut off the view in 
that direction, and it was only at rare intervals, and usually at sun- 
set, that we were able to see the snowy crown of Lassen Butte 60 
milesaway. Even Castle Crags, almost at our feet, were rarely visible. 
This experience is frequent in the west; and of the hundreds of persons 
who visit the Pacitic slope every summer to see the mountains, few see 
more than the immediate foreground and a haze of smoke which even 
the strongest glass is unable to penetrate. 
Along the railroad between the head of Sacramento Canyon and 
Shasta Valley one traverses desolate tracts which a few years ago were 
covered by a noble forest of ponderosa and sugar pines. 
EFFECTS OF BURNS IN CHANGING ZONE POSITIONS. 
A burn in the lower part of the Shasta fir forest a little above 
Wagon Camp affords an excellent illustration of the way fires some- 
times change the zone relations of particular areas. The area in ques- 
tion was well within the Canadian zone before the fire, which occurred 
only a few years ago. Since the fire, Transition zone species have crept 
up the ridge, and now Ceanothus relutinus, Arctostaphylos patula, Hor- 
kelia pseudocapitata, Apocynum pumilin, Gayophytiom ramosissimum, and 
others are common. The manzanita and buck-brush are young and 
small but are spreading, so that in a few years the ridge, which has a 
warm southerly slope, will be mainly 'lransition. But in the mean- 
time a new growth of Shasta firs has started, and in ten or twenty 
years is likely to overtop and drown out the Transition zone species, 
enabling the Canadian zone to reclaim the burn. 
Such cases of alternation of zones resulting from the clearing of 
forest land are not uncommon, particularly when deforestation is 
caused or accompanied by fire. But on steeper slopes, especially rock 
slopes, if the vegetable layer is burned off, the (lower) zone which 
creeps up to replace the (higher) one destroyed becomes permanent or 
nearly so. 
It may be laid down asa general rule that the destruction of forests, 
by adinitting the sun and wind, lessens the moisture in the soil and 
increases the temperature, thus inviting animals and plants to come in 
from adjacent warmer areas. Deforestation of an area therefore tends 
to lower its zone position. 
SLOPE EXPOSURE. 
By slope exposure is meant the inclination of the earth’s surface at 
a particular point with reference to the angle at which it receives the 
su’s rays. The amount of heat, were it not for the retarding effect of 
