268 Proceedings of the Koyal Society of Edinburgh. [Sess. 
This shock was stronger than all the earlier recorded shocks in the 
Ochil district. The intensity was not less than 7 at Alva and Tillicoultry, 
while that of the earthquake of September 21, 1905, was at no place higher 
than 6. 
The only isoseismal which it is possible to draw is that of intensity 6. 
This is indicated by the continuous line in fig. 5. The curve is 15 miles 
long, 10J miles wide, and contains 123 square miles. Its centre is 3J miles 
E. 48° N. of Menstrie, and the direction of its longer axis is E. 25° N. 
The boundary of the disturbed area, which cannot be drawn with any 
approach to accuracy, differs slightly from that of the earthquake of 1905, 
for the shock was felt one or two miles farther to the south, at Falkirk^ 
Polmont, and Bo’ness, while it was not felt at Comrie, Crieff, and Monzie. 
At several places within the isoseismal 6 (Alloa, Cambus, Greenloaning, 
Menstrie, and Tillicoultry), the shock consisted of two distinct parts, 
separated by an interval of about 3 seconds, the first part being much the 
stronger. At places outside this isoseismal, only one part was observed, 
the effect resembling that caused by the fall of a heavy weight, or the 
passage of a traction engine. The average of fifteen estimates of the 
duration of the shock is 2f seconds. 
The sound which accompanied the shock was heard by 94 per cent, of 
