21S DR. CHARLES DAVISON ON THE [May 1904, 



22,000 if through Aysgarth, and 25,000 if it traversed Easby and 

 Richmond. Nothing, either in the time of occurrence or the 

 description given, throws the least doubt on the observations made 

 at these places. But, considering that at such distances they could 

 only have been furnished by exceptionally-keen observers, I think 

 that the disturbed area should be regarded as bounded by the 

 isoseismal 4, and therefore as containing about 12,000 square 

 miles. 



Nature of the Shock. 



The following accounts are given to illustrate the twin-character 

 of the earthquake and its variation throughout the disturbed area. 

 Of the places referred to, Ashbourne and Darley Dale are close to 

 the longer axis of the inner isoseismals, the former being very near 

 the epicentre ; Dnffield lies on the continuation of the shorter axis 

 of the same curves, while Quarndon and Derby are respectively 

 1| and 3 miles from it. 



At Ashbourne, two distinct shocks were felt, the first twice as long 

 as the second and also rather stronger : the impression produced by 

 both shock and sound being that a heavy article of furniture was 

 rapidly rolled in the room upstairs from east to west, and then, 

 after a pause of a second or two, was rolled a short way back again. 

 At Darley Dale there were also two parts, each of which began 

 with a low distant rumbling like the rushing of a strong wind, and 

 culminated in a violent shock as it passed underneath the house. 

 The second and stronger part was accompanied by an undulation 

 crossing the floor from the north-west ; and, immediately after its 

 last vibrations had died away, another slight shock was felt. 



Erom Derby the accounts are very numerous, but in most 

 respects they agree closely. There were again two distinct shocks, 

 each lasting 3 seconds with an interval of half a second between 

 them, and consisting of vibrations having a period of about half a 

 second. At Quarndon, a rumbling sound was first heard ; then 

 came a violent shock, as if a steam-roller had crashed into the 

 foundations of the house on the north-west side ; the rumbling 

 continued for about 2 seconds, and, before it ceased, a second shock 

 was felt, but not so violent as the first, the rumbling gradually 

 dying away on the south-east. At Dufneld only a single shock was 

 observed, a quivering motion during the loudest part of the rumbling 

 sound, which resembled that made by a muffled peal of thunder or 

 by a sudden gust of wind. 



With some exceptions, such as that last mentioned, the double 

 shock was observed in every part of the disturbed area. Towards 

 the north, it was clearly perceptible at Preston, Lytham, Aysgarth, 

 Settle, Richmond, and Doncaster ; towards the east, at Grantham, 

 Eagle, and Boston ; towards the south, at Barnt Green, Mere Hall, 

 and Hagley ; towards the west, at Shrewsbury and Vicar's Cross 

 (near Chester). There is no evidence of the usual tendency of one 

 part to become evanescent at a considerable distance from the 

 epicentre. 



