MINOR GEOLOGICAL EFFECTS OF THE EARTHQUAKE, 391 
else than revive a series of old landslide facets. This may not be apparent to an observer 
on the beach, but is quite striking when the coast is viewed in its entirety from a vessel 
off-shore. ‘These facets existed before this earthquake, and had been recognized as such. 
They are conspicuously outlined against the dark timbered slopes behind them, rising 
from 1,000 to 2,000 feet above the shore, and affording an important series of land- 
marks for the mariner. In strong contrast with these bold mountain forms is the region 
in which the Cape Fortunas landslide took place. The land here can scarcely be called 
mountainous; and while it breaks off in cliffs at the coast and is traversed by many 
fairly deep draws, it is essentially a region ef subdued relief. Great declivities are 
notably absent, except in the sea-cliffs, and even these are only a few hundred feet high. 
At the same time, evidences of former landslides may be seen on every hand. They 
are not extensive, as a rule, and are as likely to occur on gentle slopes as on steep ones. 
In a few cases only is a marked downslip noticeable, resulting in the uncovering of 
a steep scarp; in nearly every instance the dislocated mass appears not so much to have 
sheared off and dropt from its former position, as to have expanded or slumped, with 
an accompanying subsidence of its surface. The billowy and irregularly pitted appear- 
ance of these areas, together with the rank vegetation that covers them, afford the prin- 
cipal marks of identification. Both from their characteristic form, suggestive of plastic 
flow, and from their mode of occurrence, it seems reasonable to infer that ground-water 
plays an important réle in their genesis. They are apparently masses which have 
changed their shape in obedience to a lessening of cohesion in their interior, through 
saturation with water. Whether the movement be initiated by an earth-tremor or 
not, it is in every case essentially an adjustment to a more stable position, rendered 
necessary by a change in the physical constitution of the mass. 
It is to this categury of landslides that the one at Cape Fortunas belongs. While 
there are scarps in various places at its upper end, these are really insignificant features 
alongside of the extensive tract of the slide itself. What downslipping occurred on 
these scarps was merely an incident in the entire movement. Both in the large ratio 
between its horizontal advance and its vertical drop, and in its general appearance, the 
Cape Fortunas landslide is closely analogous to the numerous lesser slides referred to; 
and there is good reason for the belief that, like them, it consisted essentially of an 
adjustment of equilibrium in a partially water-saturated mass. It probably had long 
been imminent before the earthquake started it. 
San Pablo earth-slump. — At the time of the earthquake a landslide occurred on Mills’ 
ranch, which is about 4 miles east of San Pablo. The slide is interesting from the fact 
that a previous geological mapping of the region indicated that the point where it 
occurred was on the line of a fault extending in a northerly and southerly direction 
through the Sobrante Hills. The slide was examined by Mr. Hi. 8. Larsen, who describes 
it as follows: 
There are many other landslides in this vicinity, showing that the country is subject to 
such slides. In this particular case, one of the Castro boys informed me that the main 
part of this slide began during the winter rains, and had fallen a foot or more during these 
rains. The balance of the fall occurred the morning of the earthquake. The slide is on 
the east slope of a steep hillside and extends from the top of the hill nearly to the bottom, 
about 400 feet on the slope. The width is about 1,500 feet. At the northeast corner the 
scarp is greatest, reaching perhaps 50 feet. It gradually decreases, and is very slight for 
the southwest 700 feet. On this southwest 700 feet the only evidence of a slide is the crack 
near the top of the hill. The north 800 feet of ground shows every evidence of sliding. 
The dry ground is much cracked, and these cracks extend up and down the hill near the 
scarp and along the hill where the ground has been piled up. In some places there is a 
network of cracks. On the south side of the main slide the ground has piled up about 10 
feet. This extends along nearly all of the south side, and this tendency to pile up to the 
south is shown in other places. Moreover, the north side shows that the ground has pulled 
