C. Davison — British Earthquakes of 1889. 307 



I suppose that but few previous earthquakes have afforded materials 

 so abundant for the seismologist. 



Accessory SliocTc. — It is probable that at least one slight accessory- 

 shock occurred between ten and twenty minutes after the principal 

 shock. Near Blackburn, where the intensity was V., an observer 

 residing at Wilpshire "noticed a slight recurrence of the phenomenon 

 some time afterwards — about twenty minutes." At Prestwich, the 

 intensity was about, or perhaps more than, IV., and there "another 

 but feebler shock took place — perhaps some ten minutes afterwards." 

 The evidence is clearly incomplete, but it seems most probable that 

 both accounts refer to the same shock, which, owing to its very 

 slight intensity, escaped detection elsewhere. 



Disturhed Area. — As in the previous earthquake, the places where 

 the principal shock was undoubtedly felt are indicated by small 

 discs, and those where there is good reason for believing that it was 

 not felt by small crosses (x). For the former, I have relied almost 

 entirely on the numerous accounts given in the local press ; for the 

 latter, on inquiries made in the district with the view of determining 

 the exact form of the disturbed area. In the immediate neigh- 

 bourhood of the boundary, the evidence is somewhat scanty, and 

 especially is this the case near Glossop and in the Peak country. 

 Having, as will be seen, no positive evidence from the latter district, 

 the outline in this part cannot be regarded as very exact. 



So far as we can judge from the materials collected, the outline of 

 the disturbed area seems to be approximately circular. It will be 

 seen, from the table of intensities given below, that the boundary 

 corresponds to an isoseismal line of intensity less than IV. and 

 greater than III. Outside this area, it is possible that the shock 

 may have been felt, and probable that it would have been detected 

 by any one accustomed to the observation of slight earthquakes. But 

 that it could have been felt as far as Birmingham, as one observer 

 states, is clearly impossible, first, on account of its distance from 

 the rest of the disturbed area, and, secondly, because it was not 

 registered by one of Prof. E wing's delicate seismographs erected 

 there in my cellar. 



The disturbed area, thus defined, is 56 miles from north to south, 

 and 54 miles from east to west ; and includes an area of about 

 2480 square miles. 



Time of Occurrence. — The records of the time of occurrence can, 

 unfortunately, lay claim to no great accuracy. So far as I know, 

 the earthquake was registered by no instrument of precision. Ex- 

 cluding, however, all estimates that are admittedly approximate, we 

 have the following definite records. In the immediate neighbour- 

 hood of the epicentrum, where the intensity was not less than VI., 

 it was noticed at Bolton at 22 h. 35 m. ; at Turton, at 22 h. 36|^m. 

 by one account, and 22 h. 37m. by another. Outside this range 

 and within the isoseismal of intensity V., we have the records of 

 22h. 35m. at Farnworth, of 22 h. 37m. at Accrington, of 22h. 38m. 

 at Eochdale, Hey wood, Bury, and Prestwich; of 22 h. 40 m. at 

 Tyldesley and Wigan ; and, lastly, of 22 h. 2o-|m., clearly wrong if 



