720 ED VVATTO SO ihe 
adopted the following terms descriptive of the most important 
of these; these terms include nothing very novel in the way of 
nomenclature, but are intended simply to affix definite names to 
definite things. 
Dislocation and displacement are general terms, applicable to 
any part or the whole of a fault movement. Each of the func- 
tions defined below, and to which specific names are given, may 
be called simply a dislocation or displacement. 
Total displacement is the distance which two points originally 
adjacent are separated by the fault movement; the line connect- 
ing these two points lies in the fault plane in all straight faults. 
It is occasionally possible to determine the total displacement 
directly by such criteria as the separation of the parts of an ore 
body, the intersection of a given dike with a given stratum when 
found on both sides of the fault, and in other ways; but ordina- 
rily it can only be calculated or approximately estimated from 
some of its more easily measured functions. 
The lateral separation is the perpendicular or shortest distance 
between the two parts of any continuous zonal body (such as a 
sedimentary bed), which has been separated by a fault, the dis- 
tance being measured along the fault plane. The lateral separa- 
tion may be measured: in a vertical, horizontal, or oblique line, 
according to the attitude of the bodies between which it is meas- 
ured, and in any fault it may vary from zero to the total dis- 
placement. In the case of dikes cutting sedimentary beds, of 
marked unconformity, of abrupt folds, and so on, it may be pos- 
sible to measure two or more lateral separations in a single fault. 
In this case, and in a number of others which are possible, the 
total displacement may often be calculated from the lateral 
separation, since the latter is always the side of a right triangle 
of which the former is the hypotenuse. 
The perpendicular separation is the perpendicular distance 
between corresponding planes in the two parts of any single body 
available as criterion (such as a sedimentary bed), when this 
body has been separated by a fault, the planes on each side of 
the fault being projected for the purpose of measuring, if neces- 
