GENERAL METHODS 143 



They can be held in place at top and bottom by 

 ropes running completely around the tree, and at 

 intervals between by ropes around the back of the 

 tree. Separate the poles from the tree by a num- 

 ber of inch blocks. Have ready a piece of oil- 

 cloth or oiled canvas at least as wide as the widest 

 part of the opening and as long as it is; also a 

 large number of strips of canvas five or six inches 

 wide. 



Brush the shiny surface of the oil-cloth with 

 light oil. Mix a batch of concrete, preferably 

 near the tree, making it so wet that a man stepping 

 on a pile of it will sink to his ankles. You are 

 now ready to continue filling up the cavity. First 

 hold the oil-cloth, shiny side in, against the open- 

 ing of the cavity, the top edge of it reaching a 

 few inches above the highest part of the opening 

 and tack it there with a couple of brads. Fit the 

 cloth, where it touches the ground, across the 

 opening and hold it in place with a few 

 shovelfuls of gravel. Tie a strip of canvas to 

 the bottom of one of the poles and carry it across 

 to the other pole in such a way as to hold the oil- 

 cloth in place. Carry the canvas back and forth 

 across the opening up to a point say eighteen 

 inches above the surface of the soil. Loosen the 

 oil-cloth from the brads holding it above, thus 

 exposing the opening of the cavity. The lower 

 part of the oil-cloth will of course be held against 



