Subsurface Maps and Illustrations 



909 



critical geologic analysis. As mentioned earlier, it is a very elementary 

 task to contour a sheet technically correct. The geologist must go further: 

 his map must be technically correct and geologically feasible. 



Peg Models 



The peg model is a device sometimes used to illustrate and study 

 structural and stratigraphic conditions during the development of oil 

 fields. It enables the geologist to view the behavior of the formations in 

 three dimensions and is often a most useful tool in solving knotty struc- 

 tural problems. Peg models are not ordinarily used in broad regional 



3700 



360O_ 



3500 



3400_ 



3300- 



3ZOO_ 



3IOO — 



3O0O 



h 



Surface elev. 



?Z^//////>V///////^ 



r-Dafum = 300o' 



Figure 480. Peg model of a simple dome. 



work, especially where wells are widely separated, but are better adapted 

 to detailed subsurface studies of localized areas where well control is 

 abundant. The principal objection to peg models is that they are bulky, 

 occupy much floor space, and cannot be readily moved. 



Figure 480 shows a peg model of a simple dome. The base into which 

 the pegs are inserted should be made of wood not less than one inch thick. 

 This base is painted, usually white or buff", and section and township lines 

 and other desirable surface-map features are drawn on it to the scale 

 selected for the model. At the location of each well, a one-fourth-inch 

 hole is drilled almost but not entirely through the base. Ordinarily, a one- 



