SURFACE OBSERVATION.
Underground activity, either offensive or defensive, is first observed from those points in our lines nearest to it. All enemy trenches facing a salient of our lines will be the object of particular attention and closest daily observation. This observation of the first-line trenches should disclose the presence of enemy underground works and their approximate location.
One of the difficult questions in mining is the removal of the earth. Expert miners sometimes remove the earth as far as 100 to 200 meters from the entrance to the gallery. They throw it on old ruined shelters, in shell holes, on the reverse of the trenches. But these precautions are not always rigidly observed. When the noncommissioned officer is absent, or the enemy bombards a little strongly, some one in the working party not wanting to work overtime throws several clods of earth on the parapet.