THE EARTH MOVEMENT ON THE FAULT OF APRIL 18, 1906. 87 
The comparative observations of water-stages show that the land at the locality of the 
clam patch has not recently undergone the suspected depression, as compared to land at 
the tidal station near San Francisco. If an important change has taken place at one 
locality, it has affected the other also. On the other hand, it is noteworthy that Dr. 
Southworth’s observations at the clam patch (first of its increased accessibility, and 
after of its decreased accessibility) led to two predictions as to the condition of Sali- 
corma in Limantour Bay, both of which were verified. Their success in prediction gives 
assurance that they record an actual change of some sort — a change not restricted to the 
locality of the clam patch. The two lines of evidence taken together — the leveling by 
water-plane from the tide-gage to Bolinas, and the observation of shore conditions at 
Bolinas and Limantour Bay — suggest the possibility of a general change in the relation 
of land to sea, affecting the whole coast from San Francisco to Limantour Bay. So far 
as the observations go, such a change might pertain to either land or sea. In the line 
of this suggestion it is to be noted that November 25, 1906, falls within a period of excep- 
tionally low tides at San Francisco entrance. For 21 low tides, from November 20 to 
November 30, the mean of the observed heights was 1.08 feet below the mean of the 
predicted heights. From October 17 to October 21, 1907, on the other hand, the mean 
of 10 observed tides was only 0.32 foot below the corresponding mean of predicted tides. 
The subject appears to deserve further investigation and discussion than is practicable 
while these pages are in press. . 
The observations which occasioned this postscript, while suggesting lines of enquiry 
which may profitably be followed, do not materially affect the conclusion already sum- 
marized as to local changes in the elevation of the land. A tract, including the east part 
of Pepper Island and much of the area of Bolinas Lagoon, subsided at the time of the 
earthquake, the amount of subsidence at the point of most satisfactory measurement 
being 12 inches. The region west of the fault, including the ocean coast from a point 
near Bolinas to Limantour Bay, may or may not have been uplifted at the same time, 
and may or may not have subsequently subsided. The evidence is incomplete and 
apparently somewhat conflicting. 
Special reports on the biologic evidence follow. 
