C Davison — British Earthquakes of 1889. 313 



Miscellaneous phenomena. — As it is somewhat unusual for earth- 

 quakes to be felt strongly, if at all, in pits and excavations, it is 

 worth mentioning that the Lancashire earthquake was noticed in 

 mines in several instances. In one of the collieries in the Ince 

 district, near Wigan, the shock was felt so distinctly by a party of 

 men, that a careful inspection was made by them to see if any 

 accident had happened. In the Pendlebury Colliery, "at about 

 10.30 p.m. the colliers on No. 9, East side, Eams Mine, came out of 

 their working places to the engine-house and reported to the fireman 

 that they had heard a rumbling noise in the roof of the working 

 places." At Agecroft Colliery, "only one man noticed anything. 

 He was in No. 2 pit, and when he heard the sound he went out to 

 the pony road to see if it had been caused by a fall of dirt." ^ 



Stonyhurst Observatory is about 19 miles north of Bolton, out- 

 side the isoseismal of intensity V., but still some miles within the 

 boundary of the disturbed area. As it seemed possible that the 

 magnetic instruments might have been affected by the earthquake, 

 I wrote to the late Father Perry on the subject. The letter arrived 

 during his last absence from England ; and, after his death, Mr. 

 W. C. Cameron was good enough to inform me that no trace of the 

 earthquake was shown by the magnetic curve of February 10. This 

 result is curious, considering that, shortly after several recent earth- 

 quakes, magnetic instruments in distant observatories, far beyond the 

 range of the sensible shock, have been perceptibly affected. The 

 cause of these disturbances is not certainly known, but is probably 

 due to the mechanical action of the shock, the masses of the two arms 

 of the instrument being made unequal, in order that it may rest 

 horizontally.^ If this be the case, the absence of any noticeable 

 disturbance at Stonyhurst may have been due to the fact that the 

 line joining it to the epicentrum of the earthquake is so nearly in 

 the direction of the magnetic meridian. 



Position of the Seismic Focus and Geological Belations. — The 

 faults of the Bolton district are, with a few small exceptions, 

 arranged in two systems, one running N.N.W. and S.S.E., and the 

 other nearly E. and W. Prominent among the former series is 

 the great Irwell Valley fault. This important dislocation, which is 

 shown upon the map of the earthquake, has been traced for a 

 distance of more than twenty miles, from near Poynton in Cheshire 

 to about three miles north-west of Bolton. Throughout its whole 

 course the downthrow is towards the north-east. The amount of its 

 throw is considerable, being 1050 yards at Farnworth, about three 

 miles south-east of Bolton.^ 



Now, as we have seen, both isoseismal lines are approximately 

 circular and almost exactly concentric. The centre of the smaller 

 curve (intensity V.), which is the more accurately drawn, is about 

 two miles N.N.E. of Bolton, or half a mile west of Bradshaw ; and 



^ The last two accounts are quoted from a note read by Mr. J. Knowles before the 

 Manchester Geological Society on March 12, 1889. 



2 Geol. Mag. Dec. III. Vol. II. pp. 210-211. 



3 E. Hull, Geology of the Country round Bolton, Lancashire (Geol. Surv. Mem.). 



