C. Davison — British Earthquakes. 



59 



on observations of the direction, intensity, and time of occurrence of 

 the shock in different parts of the disturbed area ; but the second 

 method alone is applicable to the earthquakes here discussed. It 

 will be seen, on reference to the maps which accompany this paper, 

 that the isoseismal lines are approximately circles or ellipses of 

 small eccentricity ; and I have assumed that the epicentra coincide 

 nearly with the centres of these areas. The correctness of the 



Edml-urgK Eartkqua^e : January IS. 1559. 



position so assigned to an epicentrum depends not only on the 

 accuracy with which the isoseismal lines are traced, but also on a 

 further assumption that their form is not greatly altered by variations 

 in the nature of the rocks within the disturbed area. Also, if the 

 seismic focus, as in the case of a fault, be inclined to the horizon, 

 the intensity must, catteris paribus, be greater on the side towards 

 which the fault slopes ; so that the epicentrum is probably nearer the 



