20, 3 Schenck: Physiography and Geology of Samar 258 
EARTHQUAKES OF SAMAR, MAY 21 TO 26, 1921 
On the afternoon of the said date at 12.45:5 a foreshock of intensity 
IV-V was felt throughout Samar, and as far as Catanduanes, Sorsogon, 
and Albay. At 16.43:21 occurred the principal earthquake, which at 
Batag affected the lighthouse apparatus, so that afterwards it refused 
to turn: no other damage was reported; yet the intensity of the shock 
must have reached degree VII at least. The observer at Batag reports 
that the jerks, both of the principal shock and of the preceding one, were 
in a nearly east-southeast and west-northwest direction. This earthquake 
shook Samar, Leyte, Masbate, and Catanduanes Islands and the south- 
east provinces of Luzon, Sorsogon, Albay, Camarines Sur, and Camarines 
Norte. 
The quake was followed by a series of aftershocks, which did not cease 
until the 26th. Our seismographs at Manila recorded seven on the 21st, 
seven on the 22d, eight on the 23d, but two on the 24th, three on the 
25th, and two on the 26th. The seismograph at Tigaon, Camarines Sur, 
recorded some few more; the seismograph of Butuan did the same. Of 
these twenty-nine aftershocks recorded at Manila, only fourteen were felt 
at Catbalogan (Batag did not send detailed list, the report says that light 
aftershocks occurred at intervals); Legaspi and Calbayog felt eight. 
In the whole series, three only reached degree IV. 
The origin of the disturbance lay certainly outside of Samar under 
the sea. Our records give an average distance of 550 kilometers from 
Manila; such a distance places the center at about 50 kilometers from the 
Northeast portion of Samar, fully in the Philippine Deep. 
October 19, 1897, there occurred in the same region a much-stronger 
earthquake, which caused considerable damage in the towns of Laoang, Pa- 
lapag, Oras, Sulat, Gandara, and Catubig: the aftershocks were frequent at 
Laoang until March, 1898. The epicenter was presumably likewise in the 
Deep. 
The anomaly of Calbayog, with only eight aftershocks, while Catbalogan 
felt fourteen, is in accordance with what happened in other instances. 
Calbayog seems reluctant to be shaken; perhaps the geological conditions 
might give some explanation. 
An explanation of this anomaly might be the distribution of 
rainfall connected with the nature of the formations near Cat- 
balogan; that is to say, the loosely consolidated sediments near 
Catbalogan when they are water-soaked would make the earth- 
quake shocks more apparent than the less-saturated beds at 
Calbayog. 
Jipapad to Laoang.—The trail from Jipapad to San Vicente 
extends across several ridges of sandstone and shale, and no 
other formation was seen during the entire journey from the 
latter barrio down Catubig River to the town of Catubig. At 
this town, there is a concrete pavement containing igneous peb- 
bles, and inquiry showed that these were obtained from a branch 
of the river that flows from the southwest. Clay and alluvium, 
only, are exposed by the river between Catubig and Laoang, on 
