THE SEQUOIA PITCH MOTH. 9 
Many trees with fire wounds are reinfested on the sound side and 
killed, thus adding to the material which makes a surface fire in the 
area really serious. The heat generated by them in burning, either 
standing or prostrate, injures and kills healthy trees in the immediate 
vicinity. 
During decades fallen timber, primarily caused by insects, accumu- 
lates and provides such an amount of inflammable material among 
the uninjured green trees that finally a fire sweeps such areas clean of 
all tree growth and enters and destroys adjoining areas which contain 
healthy trees only. 
In the infested zone in the vicinity of Rainy Lake the forest looks 
much like a checkerboard. There is an area of 50 acres here with a 
stand of 10-year-old trees on them; adjoining this is a square-cut 
piece of 200 acres with 40-year-old trees as a cover; next to this are 
80 acres on which reforestation started only a few years ago, and so 
on. This thing has been going on for at least 100 years, so far as can 
be traced, and probably existed before time was counted. Everyone 
of these variously aged tree patches is the result of a separate fire. 
The explanation of the occurrence of so many of them within an area 
comparatively so small is found in the peculiar meteorological condi- 
tions prevailing here. 
TOPOGRAPHY OF THE AREA. 
Running from the southeast toward the northwest are the rocky 
walls of the Flathead Range; west and parallel to it lies the Mission 
Range ; and on the divide between Swan River and Clearwater River, 
extending from the Mission Range toward the wagon road which 
passes over the lowest elevation, and running from west to east is a 
high ridge. This ridge forms an effective barrier to storm clouds 
driven up Swan River between the walls of the Flathead and Mission 
Ranges. Their only outlet is between that ridge and the Flathead 
Range over the Rainy Lake territory. 
The clouds driven up Swan River, inconsequent though they might 
be under different conditions, strike the ridge dividing the two water 
courses and are promptly thrown back upon their own mass by the 
resistance of the ridge. On the west are the walls of the Mission 
Range, so there is no escape for them in that direction; thus they 
drift eastward and toward the outlet over Rainy Lake. Part of them 
escape there. But the greater part are thrown upon the wails of the 
Flathead Range, from which they tumble back upon the oncoming 
mass in a turmoil before this also by and by finds its way to the only 
avenue of escape. The great numbers of lightning-struck trees in 
this area abundantly testify to the great r61e played here by lightning. 
