﻿•2 DE. CHAELES DAVISON ON THE [Feb. I905, 



wide, and 161 square miles in area. Its longer axis runs from 

 W. 30° N. to E. 30° S., and its centre is situated at a point 2 miles 

 S. 20° W. of Loughborough. The isoseismal 4 is 46 miles long, 

 32 miles wide, aud contains 1170 square miles. Its longer axis is 

 directed from W. 40° N. to E. 40° S., and its distances from the 

 isoseismal 5 are 8 miles on the north-east side and 5 miles on 

 the south-west. The isoseismal 3, which forms the boundary of 

 the disturbed area, is 59 miles long, 47 miles wide, and includes 

 2200 square miles, and its longer axis runs north-west and south- 

 east. While, however, the two latter curves are normal, or nearly 

 so, as regards their relative position, the isoseismal 5 shows a 

 marked displacement towards the north-west, the distance of its 

 centre from that of the isoseismal 4 being 8 J miles. Another 

 feature of some significance is the deviation of about 10° between 

 the directions of the axes of the two inner isoseismals. 



Over a large part of the disturbed area — ranging from Burton- 

 on-Trent to Ketton, and from Nottingham to Burbage — the shock 

 consisted of two distinct parts, separated by an interval, the average 

 duration of which was 2| seconds. The first part was the stronger 

 at Borrowash, Burton-on-Trent, and Uppingham ; while at Ketton 

 the two parts were regarded as approximately equal in intensity. 

 The evidence derived from the nature of the shock is thus incom- 

 plete ; but it is sufficient to show that, corresponding to each part 

 of the shock, a distinct impulse must have taken place within the 

 seismic focus. 



Much more definite is the evidence afforded by the isoseismal 

 lines. Prom the excentric position of the isoseismal 5 with respect 

 to the isoseismals 4 and 3, we may infer that, if a series of inter- 

 mediate isoseismals could be drawn, there would be a second group 

 of curves similarly placed with regard to the south-eastern portion 

 of the two outer isoseismals. It is evident, indeed, that these 

 lines are merely the resultants of two pairs of such curves, approxi 

 mately concentric with the geometric foci of the isoseismals as 

 drawn on the map and coinciding with those curves towards the 

 north-west and south-east ; for there is a marked absence of obser 

 vations of intensities 4 and 3 from the districts near the ends of 

 the minor axes of the curves. The component isoseismals cannot 

 be drawn with sufficient accuracy to justify their reproduction on 

 the map ; but, from their approximate paths, it follows that the 

 centre of the south-eastern isoseismal 4 coincides very nearly with 

 the village of Tugby, which is 17 miles E. 34° S. of the centre of 

 the isoseismal 5 ; and that the intensity of the vibrations from the 

 south-eastern focus died out much more slowly than that of the 

 vibrations from the north-western focus. 



Whether the north-western or the south-eastern focus was first 

 in action is uncertain, but it is clear, from the brevity of the 

 interval between the two parts of the shock and from the great 

 distance between the centres of the two foci, that the interval 

 between the occurrence of the two impulses was less than the time 

 required for the earthquake-waves to traverse the region between 



