ON MULE-BACK FROM CARICHIC. 219 
times on the slopes of the Sierra Madre 
range. This dense mass of spar and 
mast timber, as I shall call it, is nearly 
always found on the richest soil of the 
mountain, generally in the narrow little 
valleys where the silt from the sides is 
swept down by the rains until the soil is 
many feet deep. 
The great coniferous forest of the 
northern part of the Sierra Madre range 
of Mexico is probably one of the largest 
in the world (it is undoubtedly the larg¬ 
est virgin forest on either continent), and 
when its resources are opened by well- 
constructed wagon roads, or, better still, 
by a railway system, it will undoubtedly 
prove an enormous source of revenue to 
the Mexican States of Chihuahua and 
Sonora, and to no little extent those of 
Sinaloa and Durango—a source nearly as 
