THE EARTH MOVEMENT ON THE FAULT OF APRIL 18, 1906. 89 
REPORT ON A BIOLOGICAL RECONNAISSANCE OF TOMALES BAY REGION. 
By CuHarues A. Kororp. 
On October 26-28, 1906, in company with Profs. H. B. Torrey and R.S. Holway, I made 
an examination of the shore of Tomales Bay to obtain evidence of faunal modification 
resulting from the earthquake of April 18, 1906. The places specially examined were as 
follows: the northeast shore from Millerton to Preston Point; Hog Island near the mouth 
of the bay; the southwest shore from near Tomales Point to the region opposite Marshall, 
and from Inverness to the head of the bay. The outer face of Tomales Point was also 
explored for a short distance near “Shell Beach.” 
Search was made for evidence of a change in level in the two sides of the bay and arene 
for evidence of depression of the northeast shore and elevation of the southwest shore. 
For this purpose critical examination was made of barnacles in situ on rock in place along 
the shores between tide levels. The fauna of the bay includes no generally distributed 
organisms attached to rock within tide levels except the barnacles (Balanus sp.). Mussels 
are rare and there are very few attached seaweeds far from the mouth of the bay. 
The barnacles are, however, sufficiently abundant and widely distributed to afford an 
excellent index to any recent change in levels. If the northwest shore line, about 0.5 to 
1.5 miles from the main earthquake trace, had been deprest even a few inches we might 
expect to find young barnacles, the young of the year which are easily distinguished by 
their brownish-gray color, softer texture of the shell, and certain structural features, in- 
vading the new territory above the old to an extent equivalent to the depression. If the 
southwest shore had been elevated, we should expect to find a number of dead barnacles in 
the region above the old barnacle limit and a relative absence of young in the upper levels. 
The upper limit of the growth of barnacles lies below the level of highest tides, and is more 
or less distinctly marked, according to the exposure to prevalent currents and wind and to 
exposure to the sun; and it is also modified by the slope and texture of the substratum. 
The two shores present strong contrasts in the matter of exposure to prevalent winds, 
to the sunshine and in the texture of the substratum, the rocks of the northeast shore be- 
longing to the Franciscan, more or less metamorphosed, and those of the southwest shore 
being of a granitic nature. These contrasts produce considerable modifications in the dis- 
tribution of the barnacles. 
A critical examination of the data reveals no conclusive evidence of any recent change in 
the distribution of barnacles that can be attributed to a change in the levels of rocks in place. 
There is no sharp and uniform contrast between the two sides of the bay in the matter of 
the distribution of these organisms. ‘There is no uniform or extensive invasion of higher 
levels by young barnacles on the northeastern shore and no marked destruction of old 
barnacles and absence of the young at high levels on the southwestern shore. The conclu- 
sion is reasonably certain that there has been no appreciable change in levels of either shore 
as a whole. 
Especial care was taken with the examination of the rocky shores of Preston Point 
which is crost by the main fault, but even here there is no biological evidence of a change in 
levels on the two sides. In many regions barnacles have been killed in great numbers, 
apparently by silt in the waters. In other cases barnacle-coated substrata have been shifted 
with the mud, sand or gravel in or on which they lie, but such changes are of a local or super- 
ficial character. Hog Island, which lies very near the line of the fault but is not crost by it, 
shows no uniform change in its barnacle fauna. The outer sea-cliff of Tomales Point, tho 
very much shattered and with considerable talus from rock falls resulting from the earth- 
quake, shows no disturbances in its fauna traceable to seismic movement. Local testi- 
mony of dealers in fish, of fishermen and of clam diggers indicates a great falling off in ship- 
ment of clams since the earthquake, traceable to departure of clam diggers, destruction of 
clams in places, by shifting of clam beds or their burial with detritus from cliffs. No change 
of levels which might not be traceable to shifting of loose deposits was noted. 
There was local testimony of increased wash along the railroad embankment skirting 
the northeastern shore, or sinking or rising of known shoals in the bay, and of a depression 
of the gravel spit on which the fishing village stands. Probably all of these phenomena 
are explicable as the results of local loosening up of the railroad embankment and shifting 
of loose deposits, rather than as a result of a general movement of the earth’s crust. 
