170 Br. C. Davison — British Earthquakes, 1893-99. 



upper margin of tlie focus. Thus, the fault-line should traverse 

 the district between the centre of the disturbed area and its eastern 

 boundary. 



The faults of the district have been mapped b}^ Professor Judd 

 and described in his well-known memoir.^ The more important 

 ones have a W. by N. and E. by S. direction, with throws in some 

 places of not less than 150 feet towards the north. The two chief 

 faults are the Billesden and Loddington fault (traced for about 



7 miles) and the Tinwell and Walton fault (about 14 miles in 

 length), and between them are several others which have a parallel 

 direction, Eunning transversely to these east and west faults are 

 a number of others of smaller throw and with a general north and 

 south direction, apparently representing cross fractures. A group 

 of these is shown in the south-east corner of the map ; one of which, 

 passing by Ketton and Duddington, can be traced for a distance of 



8 miles. Its throw seems to be greatest in the central part of its 

 course, to the west of Collj^weston ; near Duddington it probably 

 amounts to about 40 or 50 feet. At its north end it bends round 

 to a north-westerly direction, and in tliis part its hade is evidently 

 towards the west. The most easterly fault of the group runs about 

 N.N.W. and S.S.E. 



"That the faults mapped and described include all which traverse 

 the area," Professor Judd remarks, " is by no means probable. 

 Over considerable areas clays of enormous thickness prevail without 

 any well-defined hard beds, and among these it would be impossible 

 to detect dislocations while running the geological lines ; other large 

 areas are hopelessly concealed from our observation by thick masses 

 of Boulder Clay, and of some of the faults actually detected it is not 

 possible to trace more than a small part of their course, owing to the 

 same causes." (p. 259.) 



Possibly this may account for the termination on the map of the 

 Ketton and Duddington fault towards the north, just after it crosses 

 the river Wash and enters a mass of Lincolnshire Oolite. If the 

 fault does not really end at this point, but is continued roughly in 

 a N.N.W. direction, it would satisfy all the conditions implied by the 

 seismic evidence. Whether it be to a slip of this fault, or of another 

 transverse fault not shown on the Survey map, that the earthquake 

 was due, it is clear that the displacement must have been very small 

 to produce so slight a shock. The horizontal length of the focus may 

 have amounted to two or three miles, and the displacement probably 

 died out more slowly towards the south, giving rise to a broader 

 lateral margin, and thus causing the sound-area to overlap the 

 disturbed area in that direction. 



Comrie Earthqualce : Aug. 22, 1898. 



To the seismologist, the recent Comrie earthquakes are of interest 

 as members of a long series of shocks and sounds, now perhaps 

 drawing for the present to a close. To the geologist, they may be of 



1 " The Geology of Eutland" : Geol. Surv. Mem., 1875, pp. 256-259. 



