72 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. — 
The phenomena of vertical displacement are in general so irregular as to indicate that 
they were determined chiefly by surface conditions. Where the ground sloped toward 
the northwest the horizontal throw caused an 


Granary 

Cow Barn 
apparent vertical downthrow to the northeast. 
(Plate 48a.) Where the ground sloped toward 
the southeast an apparent vertical throw to the 
southwest was produced. Where the fault- 
trace followed a narrow sag interrupting the 
side slope of a ridge, the apparent vertical throw 
was on the side toward the ridge, as indicated 
in the diagram, fig. 6. 
48p.) The only unqualified record of vertical 
displacement is on Pepper Island in Bolinas La- 
goon, where the mean of seven measurements 
shows a downthrow of 12 inches on the north- 
east side. The question whether the faulting 
along the plane of rupture was accompanied by 
the elevation or depression of large areas will 
(See also plates 108 and 
Fence , be discust in another place. 
Fic. 22.— Plan of Skinner premises, showing char- Movement normal to the Jault-plane. — Where 

acter of displacements measured. The broken 
lines show positions of bushes, path, and 
the fault-trace is a trench, imperfectly filled by 
fence before earthquake in relation to objects fragments of soil and rock, it is clear that the 
west of fault; also position before earthquake 
of corner of barn with reference to ground east 
walls of the fault stand farther apart than before 
of fault. the earthquake. Where the fault-trace has the 
echelon phase and consists of a system of cracks, 
not accompanied by visible elevation of the surface, it is also evident that the walls 
stand farther apart. Where the fault-trace is a ridge, composed of fragments of soil, 
with more or less interstitial void, it may be assumed that the voids are at least equiva- 
lent to the ridge in volume. As the fault-trace is made up 
almost wholly of these three phases, it follows that in the visi- 
ble part of the fault its walls did not approach as a result of 
the faulting but receded a little. 
In this connection mention may be made of the fact that 
at the Shafter ranch a fault crevice was momentarily so wide 
as to admit a cow, which fell in head first and was thus 
entombed. The closure which immediately followed left 
only the tail visible. At this point the fault-trace was a 
trench 6 or 8 feet wide, and the general level of the soil blocks 
within it was 1 or 2 feet below that of the adjacent undis- 
turbed ground. 
One suggestion in connection with the recession of the 
fault walls near the surface of the ground is that temporary 
stresses incidental to the faulting caused permanent com- 
pression of the adjacent terranes. It is a fact familiar to 
engineers that most superficial formations, while in their 
natural, undisturbed condition, have a structure involving 
voids, and that they may be comprest by overpowering this 
structure. But, if I understand the matter, such formations 
Fig. 23. — Dislocated road shown 
in plate47B. Parallel lines rep- 
resent wheel tracks. Ramify- 
ing lines indicate cracks of 
fault-zone. 
are not compressible (except elastically) when their voids are full of water, so that 
accommodation for dilatation of the fault-zone could have been made in this way only so 
far as the ground was dry. As the ground was full of water in many places — including, 
