92 



OLASSIFICATIOW OP THE PUBLIC LANDS. 



established by dividing the difference between the depth limit and 

 500 feet by the normal value at the surface, each 40 acres can be 



DOLLARS PER ACRE 



valued accordingly. The average depth of coal in a forty that is 

 crossed at an angle by the outcrop or the depth-contour lines is the 

 depth at the geometrical center of the area underlain. 



