374 THE OCHIL EARTHQUAKES OE ] 900 TO 1907. [Aug. I907, 



which has not affected perceptibly the structure of the district, must, 

 I am afraid, remain for the present in doubt. 



Assuming them, however, to be connected with a single origi- 

 nating fault, the portion of the fault-surface affected by the recent 

 displacements must extend from near Airthrey to a mile east of 

 Tillicoultry, a distance of about 8 miles. In the two stronger 

 shocks of September 1900, the centres of the foci lie about a mile 

 east of Menstrie. Neglecting the two small creeps in 1903 and 

 April 1905, the next and easternmost slip occurred in July 1905, 

 the centre of the focus being about 2| miles east of Menstrie. 

 This was followed two months later by the greatest displacement 

 of all, the centre of which lies about If- miles east of Menstrie. 

 The succeeding slips were all confined within a comparatively-small 

 region of the fault, the centres of the foci in the four shocks of 

 October 8th (7.24 and 8.16 a.m.), December 28th and 30th (4.15 

 p.m.), 1906, being all within half a mile of Menstrie. The majority 

 of the slight slips which took place between September 1905 and 

 April 1907 affected a very small region of the fault close to Menstrie, 

 but a few — such as those on September 28th, October 3rd and 

 26th, December 30th (2.10 p.m.), 1906, and March 19th, 1907— 

 probably occurred about a mile west of that village. 



EXPLANATION OF PLATE XXVI. 



Map illustrating^the area affected by the principal earthquake of September 21st, 

 1905, on the scale of 6 miles to the inch. 



Discussion [oisr the two foregoing papers]. 



The Chairman (Dr. A. Strahan) said that geologists were greatly 

 indebted to the Author for his painstaking collection of observations 

 upon earthquakes. The symmetry of the isoseismal lines was 

 remarkable. They appeared, moreover, to have been traced with 

 such precision as to have enabled the Author to locate ' an origi- 

 nating fault ' and to have determined its hade. It was to be noted, 

 however, that the region dealt with in the first paper was honey- 

 combed with workings for coal, and that all the faults were well 

 known. No fault was known to exist in the position assigned to 

 the * originating fault.' 



