Subsurface Maps and Illustrations 911 



fourth-inch iron rod is used for the pegs, which, in turn, are to represent 

 the wells. 



The plane of the board is the elevation datum for the model. This 

 assumed elevation should be somewhat below that of the lowest bottom- 

 hole elevation in the field. Thus, if the lowest bottom-hole elevation is 

 2,300 feet above sea level, then the model might be constructed with the 

 base elevation at 2,000 feet. 



The rods are cut to lengths equal to the surface elevations of the 

 wells on the vertical scale selected, plus an amount equal to the depths 

 of the holes into which they will be mounted. The formations penetrated 

 by the wells are represented on the rods by bands painted in different 

 colors. 



After the rods are cut, painted, and set in their respective locations, 

 the formation tops from well to well are shown by strings colored the 

 same as the formations which they represent, as indicated in figure 480. 

 When all the rods are connected with the colored strings, the planes of 

 the formations can be seen in their approximate relationships to one 

 another. Of course, this illustrative method does not permit showing the 

 curved surfaces of the structures, but it does suggest them in the sloping 

 planes of which the strings are elements. 



Solid Models 



The solid relief model of a structure can be made in much the same 

 way as a topographic relief model, if there is a good structural contour 

 map of the area. 



The contour map is used as a pattern. Since the map will be cut dur- 

 ing the construction of the model, several copies should be on hand. 

 Sheets of pressed-fiber wallboard such as Celotex are cut with a coping 

 saw along each contour line, as shown in B of figure 481. When the first 

 sheet is mounted on the base, the next-higher contour is transferred to it, 

 as shown by the dashed line in the figure cited. This may be done with one 

 of the uncut maps and carbon paper. The transferred line serves to fix 

 the position of the next fiber-board sheet, as in C of figure 481. When all 

 the contours have been cut and the sheets are firmly nailed down, the skele- 

 ton of the model will look like D of figure 481. This skeleton should be- 

 partly waterproofed with several coats of shellac, after which it may be 

 covered "yvith plaster of paris, papier-mache, or a similar material. Care 

 must be taken to use only a sufi&cient thickness of the covering material 

 barely to cover the edges of the fiber-board contours, or the accuracy of 

 the model may be impaired. 



If it is desired to show the structure contours on the finished model, 

 pins may be stuck in the edges of the blocks before the covering material is 

 applied. The pins will later serve as guides for sketching the contours and 

 can easily be pulled out when they have served this purpose. 



The solid model is used principally as an aid in teaching. Unlike 



