THE MEASUREMENT OF FAULTS 729 
tionship to the lateral separation, as the lateral separation does 
to the total displacement. 
The terms which have been adopted above have purposely 
been made as few as is consistent with the plan of furnishing a 
scheme for complete fault-analysis. The number might be 
increased indefinitely ; yet ordinarily this is undesirable, for most 
other fault measurements are simple mathematical functions of 
the terms above adopted, and can be easily reduced to one of 
these; and the great multiplication of terms leads to confusion 
in a study which is at best not too simple. In specific instances, 
however, it may be desirable to increase the number of terms, and 
to give separate names to other fault measurements. 
J. EDWARD SPuURR. 
