THE USE OF MODELS IN THE INTERPRETATION 
OF DATA FOR DETERMINING THE 
STRUCTURE OF BEDDED ROCKS 
MAURICE G. MEHL 
Of the various ways to describe the structure of sedimentary 
beds graphically, that of showing the configuration of the datum 
bed by contours is by far the more common and, for most cases, 
altogether the more satisfactory method. Ordinarily the struc- 
tural contour map is drawn from irregularly scattered observat- 
ions — elevations on a key bed or on other horizons from which 
the elevation of this bed may be calculated. 
At best the determination of the structure of a region is an 
approximation. It is rare indeed that a single bed has unlimited 
exposures over a large area and even with supplementary obser- 
vations from sub- and superadjacent beds, within a compara- 
tively large proportion of almost any region, no data are to be 
had. Usually, then, the observations are closely crowded along 
the limited outcrops and are relatively far apart over most of 
the area. 
Although in general the principles of contouring topography 
and structure are the same, the details are somewhat different. 
Since topographic contours attempt to represent accurately the 
configuration of a surface, every point on that surface is a valid 
observation and the greater the number of observations the 
more accurate the resulting contour map. In contouring the 
structure, although the contours represent a certain condition 
of the bed it is not the configuration of its surface. What is to 
be shown is the structural attitude, the attitude of the general 
plane of the bed as it has been modified by diastrophism alone. 
This is not necessarily the upper or lower surface nor even the 
present attitude of the general plane of the bed as is pointed out 
later. 
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