1915-16.] The Ochil Earthquakes of the Years 1900-1914. 287 
Of the earthquakes of the first class, that of 1905 originated in the 
east-central region, that of 1908 in the eastern region, and that of 1912 in 
the west-central region, the isoseismal centres of the two last being 
respectively 1 mile east and 24 miles west of the centre of the first. One 
effect of the principal slip of 1905 was evidently to cause a sudden increase 
of stress within and just beyond the lateral margins of the focus, the stress 
near the eastern margin being relieved by the principal slip of 1908, and 
that near the western margin by the principal slip of 1912. 
The distribution of the epicentres of the earthquakes of the second and 
third classes are shown in Table IY, the figures being percentages of the 
total number for each interval : — 
Table IY. 
W. 
w.c. 
E.C. 
E. 
Before Sept. 21, 1905 
33 
67 
Between Sept. 21, 1905, and Oct. 20, 1908 . 
8 
24 
68 
Between Oct. 20, 1908, and May 3, 1912 
25 
22 
53 
After May 3, 1912 
50 
19 
31 
Thus, during the first twelve and a half years, seismic activity predominated 
in the east-central region, and during the last two and a half years in the 
western region, no minor epicentre throughout the whole fifteen years 
being confined to the eastern region. 
It is perhaps worthy of notice that, in the Inverness earthquakes of 
1901, there was the same oscillation of epicentres in the central region, 
ending with a progression of activity towards the west. In the Inverness 
earthquakes of 1816 and 1890, the concluding after-shocks were marked by 
the same westerly migration beneath the bed of Loch Ness. 
( Issued separately February 6, 1917.) 
