It is highly probable, however, that when the tree is felled the trunk strikes across a rock or another log, and the impact causes actual failure in the log as in a beam.
_Resin_ or _pitch pockets_ are of common occurrence in the wood of larch, spruce, fir, and especially of longleaf and other hard pines.

They are due to accumulations of resin in openings between adjacent layers of growth.

They are more frequent in trees growing alone than in those of dense stands.

The pockets are usually a few inches in greatest dimension and affect only one or two growth layers.

They are hidden until exposed by the saw, rendering it impossible to cut lumber with reference to their position.