THE SEQUOIA 313 



actions on the trunk is the boring of those great 

 tunnel-like hollows through which horsemen may 

 gallop. All of these famous hollows are burned 

 out of the solid wood, for no Sequoia is ever 

 hollowed by decay. When the tree falls the brash 

 trunk is often broken straight across into sections 

 as if sawed ; into these joints the fire creeps, 

 and, on account of the great size of the broken 

 ends, burns for weeks or even months without 

 being much influenced by the weather. After 

 the great glowing ends fronting each other have 

 burned so far apart that their rims cease to burn, 

 the fire continues to work on in the centres, and 

 the ends become deeply concave. Then heat be- 

 ing radiated from side to side, the burning goes 

 on in each section of the trunk independent of 

 the other, until the diameter of the bore is so 

 great that the heat radiated across from side to 

 side is not sufficient to keep them burning. It 

 appears, therefore, that only very large trees can 

 receive the fire-auger and have any shell rim left. 

 Fire attacks the large trees only at the ground, 

 consuming the fallen leaves and humus at their 

 feet, doing them but little harm unless consider- 

 able quantities of fallen limbs happen to be piled 

 about them, their thick mail of spongy, unpitchy, 

 almost unburnable bark affording strong protec- 

 tion. Therefore the oldest and most perfect 

 unscarred trees are found on ground that is 

 nearly level, while those growing on hillsides, 



