254 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
points lies in the fault plane in all straight faults. It is occasionally possi- 
ble 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 ordinarily 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 distance being measured along 
the fault plane. The lateral separation may be measured in a vertical, 
horizontal, or oblique line, according to the attitude of the bodies between 
which it is measured, and in any fault it may vary from zero to the total 
displacement. In the case of dikes cutting sedimentary beds, of marked 
unconformity, of abrupt folds, and so on, it may be possible to measure 
two or more lateral separations in a single fault. In this case, and ina 
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 crite- 
- rion (such as a sedimentary bed), when this body has been separated by a 
fault, the planes on each side of the fault bemg projected for the purpose 
of measuring, if necessary. The perpendicular separation thus has a cer- 
tain relation to the lateral separation; for it constitutes the side of a right 
triangle, the hypotenuse of which is the lateral separation, except in the 
possible case where the perpendicular and lateral separations coimeide. 
This mathematical relation makes it often*possible to estimate the 
lateral separation from the perpendicular separation, and from the latter 
the total displacement. Of these three functions, the perpendicular separa- 
tion is most easy of measurement, and its value may vary from zero to the 
full amount of lateral separation. The lateral separation is easier to ascer- 
tain than.the total displacement, and its value may vary from zero to the 
total displacement. 
The measurements which have been defined have no constant direc- 
tion, since they refer to fault movements which are capable of infinite 
variation. In general geological work, however, it is often only possible 
