74 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
vertical or horizontal throw. In general they were not parallel with one another nor 
were they otherwise systematically arranged, except that some of them were apt to 
oecur along the boundary between alluvium and a firmer formation. They were ram- 
bling rather than straight and were often branched. They ranged in width from a 
fraction of an inch to several inches. They were seen from the train in the bottom- 
land of Papermill Creek within a mile of Point Reyes Station. They were also seen 
in the delta of Papermill Creek, in the bottom-land of Olema Creek near Olema, and 
in the delta of Pine Gulch Creek. They were seen in the bottom-lands and deltas of a 
number of small creeks entering Tomales Bay from the west between Inverness and the 
head of the bay. Other localities were tidal marshes at the head of Bolinas Lagoon 
(plate 49n), at the head of Tomales Bay, and in small estuaries near Inverness. They 
were seen in the marsh of Bear Valley Creek near where the stream joins Papermill 
Creek; and a road embankment crossing that marsh was elaborately cracked and faulted 
thru much of its extent. 
It is noteworthy that the neighboring road crossing a marshy portion of the Paper- 
mill delta was much less cracked, and the difference is probably to be ascribed to the 
difference in height and strength of the two embankments. ‘The thinner one suffered 
the more. 
The localities enumerated are merely those which came under observation. Within 
the zone of high intensity no marshes and no bottom lands were seen which did not 
exhibit cracks, and I regard their cracking as a general phenomenon. ‘The elaborate 
cracking of a roadway across one of the marshes seems specially significant. In the 
adjacent soft marsh close attention was necessary to discover cracks. To a large extent 
they were concealed by the vegetation, and it is probable also that many which were 
opened during the earthquake agitation immediately closed again and were practically 
obliterated by the welding of the mud. But the road embankment, being free from 
vegetation and composed of comparatively rigid and brittle material, retained all the 
cracks made during the agitation, and thus served to record the thoro shattering of an 
unconsolidated formation when subjected to strong vibration. (Plate 50.) 
Another class of superficial cracks affected hillsides, penetrating only the coating of 
loose material — decomposed rock and taius. The conspicuous individuals of this type 
are those that follow contours. Along these there was often a notable width of crack, 
accompanied by a settling on the down-hill side, and many cracks of this type are still 
visible. They are in effect the heads of incipient landslides and might with equal 
propriety be described under another caption. They are numerous thruout the Rift 
belt and fairly abundant on steep hillsides for more than a mile to the west. East of 
the Rift they are inconspicuous and believed to be rare. Some of the best examples 
are on the northeastern slope of Mount Whittenberg, about a mile from the fault-trace, 
the locality being favorable for observation because of the absence of forest. 
Superficial cracks of a third type are connected with side-hill roads. (See plate 51.) 
In such roads there is usually a notch cut in the hillside and the excavated material is 
thrown outward so as to make an embankment. The roadbed thus consists in part of 
the natural formation and in part of an artificial and relatively loose embankment. In 
the loose material, and frequently along the line separating it from the firmer ground, 
cracks were extensively developed, often accompanied by evident settling of the outer 
bank. Their magnitude depended in part on the character of the material, but in large 
part also on the intensity of the earthquake. Where they were of such magnitude as 
to injure the roadway they were soon obliterated by road repairers, and elsewhere they 
tended to disappear in consequence of the traffic; but while they lasted they constituted 
an excellent gage of intensity, and much use was made of them in districts where there 
were few buildings. 
