BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 20, pp. 171-196 May 5, 1909 



GEOMETEY OF FAULTS 1 



BY HARRY FIELDING REID 



(Presented before the Society December 29, 1908) 



CONTENTS 



Page 



Introduction 171 



Nomenclature 172 



A system of projection 173 



Classification of faults 177 



Parallel displacements 178 



Plane strata 178 



Data required for determination of shift 178 



Strike-faults 170 



Diagonal faults 180 



Folded or contorted strata 186 



Rotatory displacements 187 



Simple rotation without translation. . ■ 187 



Rotation with translation 180 



Special difficulties 193 



Possible displacements 194 



Conclusion 195 



Introduction 



Two years ago Mr F. L. Bansome called attention to the confusion 

 existing in the nomenclature of faults and noted that in the case of 

 diagonal faults it is frequently impossible to say whether we are dealing 

 with a normal or a reversed fault, or to determine whether a line at right 

 angles to the fault-plane has been shortened or lengthened. 2 The dis- 

 cussion which followed confirmed Mr Ransome's statements. Tt also 

 showed that the actual movements which have taken place in the case of 

 faults in which there is a component parallel with the fault-strike have 



1 1 wish to acknowledge my indebtedness to Mr G. K. Gilbert, who kindly read over 

 this paper in manuscript and made a number of important suggestions which have been 

 embodied in the text. 



Manuscript received by the Secretary of the Society January 9, 1909. 

 2 "The directions of movement and the nomenclature of faults." Economic Geology, 

 1906, vol. i, pp. 777-787. 



XIV— Bull. Geol. Soc. Am., Vol. 20, 1908 (171) 



