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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 22 (1938)

Issue: 9. (September)

First Page: 1261

Last Page: 1271

Title: Problem of Two Tilts and the Stereographic Projection

Author(s): D. Jerome Fisher (2)


Harker's solution of the problem of two tilts is shown to be erroneous for the general case. This problem may be worked rapidly and accurately in terms of the normals to the bedding planes by means of a tracing paper laid over a meridional stereographic net. In an appendix the meridional stereographic net is simply described and the same problem is worked in terms of the bedding planes themselves. It is believed that this discussion will furnish the trained geologist with a sufficient background to work nearly any problem involving lines and planes which can be considered to pass through the point of observation in the field. Such problems may involve bedding, fault, joint, or cleavage surfaces, which in many cases may usefully be regarded as planes for short distances; a so lines or directions within these surfaces--such as slickensides, outcrop of beds or faults, elongation of minerals in cleavage surfaces, flow lines in flow layers--may be rotated from the direction of observation in the field into any desired plane. After a little practice such problems are more easily visualized by students when so handled than when descriptive geometry is used, and the solution is attained much more quickly and simply by these direct graphical methods.

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