C. Davison— British Earthqua'kes of 1889. 309 



with the position of the place of observation relatively to that of 

 the seismic focus, or with the geological structure of the surrounding 

 country. 



Now, a single vibration was felt at : {a) Blackburn, Bury, 

 Melthara ; (h) Bolton, Hey wood, Eamsbottom, Wigan ; a double 

 vibration at : (a) Longridge, Prestwich, Ehodes ; (&) Burnley, 

 Leigh, Marbury, Nelson ; three or more vibrations at: (a) Chorley, 

 Failsworth, Hollinwood, Middleton, Stretford, VVhitefield; and, lastly, 

 a tremulous or continuous vibration at: (a) Bowdon, Crompton, 

 Darvven, Manchester, Preston ; (&) Leftwich, St. Helens, Tottington. 

 The direction of the Irwell fault in the neighbourhood of the 

 epicentrum is approximately N.W. and S.E., and, if lines be drawn 

 through the epicentrum from north to south and east to west, they 

 will divide the disturbed area into four quarters, so that places on 

 the N.W. and S.E. quarters ai-e more nearly in a line with the 

 Irwell fault than places in the N.E. and S.W. quarters. Places in 

 the former pair of quarters are preceded by the letter (a) in the 

 above list, and places in the latter pair by the letter (6). The results 

 may thus be summarized : — 



a. b. Total. 



Single Tibration 3 ... 4 ... 7 



Double or multiple vibrations 14 ... 7 ... 21 



In the majority of cases, then, double or multiple vibrations were 

 felt at places nearly in a line with the Irwell fault at Bolton ; and 

 a single vibration at places whose directions relatively to the 

 epicentrum are nearly at right angles to this direction. 



On the vertical component of the motion, very few observations 

 "seem to have been made. The movement is described as an up- 

 heaval simply, at Chorley, Eccles, Farnworth, Nelson, Oldham, 

 and Wigan ; but it is not stated whether the upheaval was followed 

 or preceded by a lowering, or even whether it was accompanied 

 by any such movement in a contrary direction at all. These places 

 are not confined to any particular part of the disturbed area. On 

 the other hand, at the following places, there was first a rise, 

 followed by a lowering of the gi'ound. 



Eamsbottom : persons felt as though they had been bodily lifted 

 up and dropped quickly. 



Heywood : the sensation was that of a sudden lifting of the^ 

 dwelling and of as sudden a sinking. 



Bury : persons in bed felt as if their beds were raised for a brief 

 time and then allowed to fall. 



Prestwich : a jerk up and down, followed by a trembling 

 movement. 



These four places, it is important to notice, lie on the north-east 

 side of the Irwell fault, and at only a few miles distance from its 

 intersection with the surface. 



Duration. — If, as I believe, the earthquake was due to a slip of 

 the Irwell fault in the neighbourhood of Bolton, and if that slip 

 was confined, not to a point, but to a definite area, we should expect 

 the duration of the shock, as well as its nature, to vary throughout 

 the disturbed area. The duration should of course be greatest at 



