If the form of a fold is conical, important elements of its geometry are the attitude of its axis and the degree of conicity (i.e. the size of the semi-apical angle of the cone). (If the fold is cylindrical this angle is 0°; but as the semi-apical angle increases to 90° as a limit, the cone approaches a plane.) These elements of a conical fold can be calculated, given the attitudes of a number of planes tangential to the fold surface. Also the standard deviation of the observations from the ideal can be calculated and used to test the structural homogeneity of a given area. Previous solutions to this problem lead to ambiguous answers, as shown by C. S. Venkitasubramanyan (this issue).

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