Vol. 60.] DERBY EARTHQUAKES OE 1903. 229 



the former is not an improbable origin. In any case, owing to the 

 proximity of Hognaston to the earthquake-fault, the observation is 

 one of considerable interest. 



After-Shocks. 

 b. March 24th, about 1.45 p.m. 



The only records of this after-shock come from Abbotshulme 

 (near Rocester), Bakewell, and Tissington. There was a slight 

 tremor at all three places, and at Abbotshulme a rumbling sound 

 was heard. 



c. March 24th, about 5 p.m. 



A slight shock was felt at Brailsford, Fenny Bentley, and One- 

 cote (near Leek). There is no record of any accompanying sound. 



d. Mav 3rd, 9.22 p.m. 



Intensity, 5; centre of isoseismal 4, lat. 23° 24' N., long. 1° 399' W. 

 Number of records, 62, from 42 places in Derbyshire, and 11 from 10 places 

 in Staffordshire ; and 35 negative records from 30 places. 



Time of Occurrence. 



As the earthquake was not recorded by any seismograph, we 

 have to rely on local observations of the time of occurrence. The 

 time given above was that determined by two signalmen in different 

 boxes on the railway-line between Derby and Duffield. It agrees 

 closely, moreover, with the mean of all the more careful obser- 

 vations, namely, 9.21J p.m. 



Isoseismal Lines and Disturbed Area. 



On the map of this after-shock (fig. 2, p. 230) are shown six curves, 

 the isoseismals 5 and 4 being indicated by continuous lines, the 

 boundary of the disturbed area by the outer line continuous in part 

 but mostlv broken, the boundarv of the sound-area bv the dotted line, 

 while the two inner isoseismal lines of the principal earthquake are 

 indicated by broken-and-dotted lines. The isoseismal 5 is 10| miles 

 long, 5 \ miles wide, and about 44 square miles in area. The 

 isoseismal 4 (the most accurately drawn of the series) is 19 miles 

 long and 12 miles wide, and contains about 179 square miles. Its 

 centre is about one mile south-west of Hognaston, and the direction 

 of its longer axis is X. 25° E. and S. 25° W. The course of the 

 boundary of the disturbed area is doubtful, except in the neigh- 

 bourhood of Derby, Bipley, and Cbeadle. As drawn, it is 31 miles 

 long, 24 miles wide, and about 585 square miles in area. The 

 distances between the isoseismals 5, 4, and that which forms the 

 boundary of the disturbed area, are respectively 3*7 and 6-4 miles 

 on the north-west side, and 3*0 and 5*0 miles on the south-east 

 side. Taking account of possible error in the tracing of these 

 curves, it follows that the originating fault must, in the neigh- 

 bourhood of the focus, run about N. 25° E. and S. 25° W., hade 



