164 REID ET AL. REPORT OX NOMENCLATURE OF FAULTS 



of Faults. This Committee was charged with recommendiiig a proper 

 nomenclature. A preliminary report was made at the Washington meet- 

 ing, December 30, 1911, and was printed as a special brochure by order 

 of the Council, under the title "Proposed Xomenclature of Faults." 

 Copies were sent to all Fellows of the Society and a few other geologists 

 with the request that it be freely criticised. The Committee received a 

 number of letters containing apt criticisms and making useful sugges- 

 tions. As a result of these letters and the discussion at the Xew Haven 

 meeting, December 28, 1912, some important changes have been made in 

 the preliminary report. The Society ordered that the revised report be 

 published in the Bulletin, in order that Fellows might give the nomen- 

 clature a working test before any official action should be taken by the 

 Society. 



In carrying out its instructions the Committee has been guided by the 

 following principles : 



1. To introduce as few technical words as possible; it is unnecessary to 

 have a technical word to denote the component of the displacement in 

 every direction in which it may be measured. 



2. To use words which suggest the technical meanings to be attached 

 to them. 



3. To make no changes in words which have a recognized meaning, 

 and to follow the best usage where a word is used in different senses. We 

 are not dealing with a new subject, but are attempting to standardize the 

 words now in use and . to adapt them to a broader conception of fault 

 movements. "We believe that no system of nomenclature will be accepted 

 which breaks with the best present usage. This makes it impossible to 

 adopt a system which is perfectly logical. 



4. To make the classification geometric and descriptive, not genetic, in 

 order that a fault may be described so far as it may have been observed 

 without any inferences as to the forces which produced it. For instance, 

 a so-called "thrust fault" may sometimes be formed without any com- 

 pression, and a "tension fault" without any tension; the terms "thrust" 

 and "gravity" faults have been frequently used. All these terms are 

 dynamic and not geometric; they should only be used after the forces 

 which produced the fault are understood. 



The discussion of the nomenclature of faults in Economic Geology, 

 which bore especially on the nomenclature of fault movements, showed a 

 wide divergence of view, some writers desiring to use descriptive terms 

 only, and some insisting that no proper classification could be made with- 

 out considering the forces producing the faults. The Committee takes 

 the former view, thinking it important to be able to describe as much as 



