64 



EARTH FEATURES AND THEIR MEANING 



the table, and on the scale of one inch to the foot. Each exposure 

 represented upon the table is " visited " and then located upon the 

 base map in its proper position and attitude. The result is the 

 field map (Fig. 47), which thus represents the facts only, unless 



FIG. 47. Field map prepared from a laboratory table. 



there have been uncertainties in the correlation of exposures or 

 in determining the position of the bedding plane. 



To prepare the areal geological map from the field map, it is 

 first necessary to fix the boundaries which separate formations at 



FIG. 48. Area! geological map constructed from the field map of Fig. 47, with two 

 selected geological sections. 



the surface ; and now perhaps for the first time it is realized how 

 large an element of uncertainty may enter if the exposures were 

 widely separated. It is clear that no two persons will draw these 

 lines in the same positions throughout, though certain portions 



