162 
MAURICE G. MEHL 
THE CONSTRUCTION OF STRUCTURE MODELS 
As a first step in the construction of the model a base sheet is 
prepared from the plane table sheets. The observation points are 
properly located and the elevation of the datum plane indicated 
at each observation. The sheet is attached to a soft board and 
at each observation point a peg is driven so that its length rep- 
resents the elevation of the bed at that point. Obviously the 
Fig. 5. “Peg” model of the data utilized in the construction of the structure 
map in Plate XX. 
board represents a horizontal reference plane the elevation of 
which is anything the worker may choose, usually slightly less 
than the lowest observation point. 
After all the pegs are fixed it is a comparatively simple matter 
to model the surface which they represent by filling in to their 
tops with fine moist sand or modeling clay. The resulting sur- 
face is full of crudities for it is composed of a series of fiat tri- 
angular surfaces extending between each set of three adjacent 
points. By slight additions of material in places and the re- 
