60 C Davison — British Earthquahes. 



intersection of the focus with the earth's surface than would he 

 indicated by the above method. Nevertheless, for the majority of 

 British shocks, the assumption seems to me admissible, for the 

 isoseismal lines in all the cases here considered are of small dimen- 

 sions, and there is no evidence tending to prove any marked irregu- 

 larity in their form, I believe that the true positions of the epicentra 

 cannot differ by more than a mile (if by so much) from the positions 

 indicated for the four principal earthquakes considered in this paper. 



In two cases 1 have attempted to assign the origin of the earth- 

 quake to the impulsive friction along well-known and prominent 

 faults. In each case, the evidence, being cumulative and far from 

 abundant, is by itself certainly not conclusive; and the deductions 

 made from it can only be regarded as at best but highly probable. 

 Taken as a whole, however, the reasons for connecting the majority 

 of non-volcanic earthquakes with such a cause are so weighty, and 

 the theory is so comprehensive of apparently disconnected phenomena, 

 that the inferences referred to are invested with a higher degree of 

 probability than that with which they would otherwise and separately 

 be endowed.^ 



The slow dying-out vibrations of very distant shocks are frequently 

 propagated to this country, and are registered by magnetic and other 

 recoi'ding instruments. More rarely are felt the perceptible vibrations 

 of earthquakes that are less distant, but still extra-British, in their 

 origin, e.g., the earthquake of May 30, 1889, which disturbed the 

 Channel Islands, the South of England, and the North of France. 

 To include either kind of shock would unduly extend the limits of 

 this paper, and I have therefore confined myself to the consideration 

 of earthquakes whose epicentra are situated within the area of the 

 British Islands. 



Of these, there were at least five during the year 1889 ; namely, 

 on Jan. 18 in the neighbourhood of Edinburgh ; on Feb. 10 in 

 Lancashire and parts of the adjoining counties ; on May 22 on Ben 

 Nevis ; on July 15 in Kintyre, Gigha Island, and Arran ; and on 

 October 7 in the east of Cornwall. In addition to these, there were 

 three others, the seismic origin of which is at present doubtful, or 

 which rest on the evidence of one observer only. 



1. Edinburgh Eakthquakes : Jan. 18, 1889. 



At least two shocks were felt at, and in the neighbourhood of, 

 Edinburgh on this day, the first at about 4h. 10m., and the second 

 at 6h. 53m. The time of occurrence of the former is variously given, 

 but, as a rule so approximately, that it is very doubtful whether the 

 existence of several separate shocks can be inferred. This may have 

 been the case, but I do not think that the evidence is sufficient to 

 prove that there was more than one shock preceding that which took 

 place at 6h. 53m. 



1 It may be well to remark here, that, excepting the sections on the geological 

 relations of the earthquakes, the following accounts were almost entirely written, 

 the isoseismal lines were drawn upon the maps, and the positions of the epicentra 

 determined, before any reference whatever was made to the geological maps of the 

 disturbed areas. 



