Vol. 58.] INVERNESS EARTHQUAKE OF SEPTEMBER 1901, 399 
by the numerous tremors and earth-sounds recorded by single 
observers’; for, in such slight disturbances, the epicentres must 
have been close to the places of observation. The numbers recorded 
in different districts near the boundary-fault are as follows :— 
Inverness and Bunchrew ......... 8 
Dochgarroch and Holm ......... 16 
Dores, Aldourie, ete. ..........4. 3 
Drumnadrochit, ete. .............6+ 6 
Thus, 8 probably originated on the north-east side of the principal 
centre, and 25 on the south-west side. 
To sum up. The great slip, which caused the principal shock, 
reached nearly from Loch Ness to Inverness, and was greatest at a 
point about halfway between. The three chief after-slips resulted 
in an extension of this area of principal displacement in both 
directions along the fault-surface, the extension towards the north- 
east being small (probably less than half a mile), while that towards 
the south-west amounted to 6 miles or more. The smaller after- 
slips (some of them mere creeps) were most numerous in three 
regions—one lying about a mile south-west of the principal centre, 
the others near Inverness and Drumnadrochit, which lie near the 
extremities of the displaced area of the fault, while in the inter- 
mediate regions they were apparently less frequent. 
In addition to the migration of the focus in the direction of the 
fault, there was also, in the six principal after-shocks, a continuous 
decrease in the depth of the focus, for the distances of the epi- 
centres of these shocks from the fault-line are respectively 1:5, 
ewe -0 0:6, 0-5, and 0-1 mile.’ 
Sympathetic earthquakes.—In the list of after-shocks, 
there are records of six shocks or earth-sounds observed only in 
the valley of the Findhorn, which lies 13 or 14 miles to the south- 
east of the boundary-fault. The times at which they occurred are: 
September 18th, about 2a.m.; October Ist, about 4.85 a.m. and 
3p.M.; October 9th, 7.40?.m.; October 13th, 12.30P.m.; and 
November 5th, 12.12 a.m.: the first two shocks being recorded by 
more than one observer. As one of these shocks was of intensity 5, 
* It should be remembered that some of these may not have been of seismic 
origin. 
Tn this case (g) the distance refers to the centre of the isoseismal 5, which 
would be somewhat farther to the south-east than the true epicentre. 
> It is interesting to notice that similar laws governed the distribution of the 
after-snocks of the great Japanese earthquake of 1891. In that. case, the area 
of displacement was 70 miles or more in length, and the after-slips affected for 
the most part a nearly central region (in which they were exceedingly numerous), 
and two more or less isolated districts near or surrounding the extremities of 
the fault. After the lapse of some months, the latter districts became prac- 
tically inactive, and there was a gradual but oscillating withdrawal of the 
after-slips to a more or less central district ; while, at the same time, the depth 
at which the slips occurred continually diminished. See Quart. Journ. Geol. 
Soe. vol. liii (1897) pp. 1-15 & Geogr. Journ. vol. xvii (1901) pp. 635-55. 
