Dr. C. Davison — Britkh EaHhquakes. 



299 



Continuing tlie isoseismal 4 in what appears to be its probable course, it 

 includes an area 31 miles long, 22 miles wide, and containing about 

 530 square miles ; the centre of the curve being about 6 miles north- 

 west of St. Agnes, while the longer axis runs from north-east to 

 south-west, or roughly parallel to the adjoining coastline. Too small 

 a part of the isoseismal 5 lies on land to allow its dimensions to be 

 even approximately determined. On the south-east side the distance 

 between the two curves is 3 miles. 



Fig. 1. — St. Agnes Earthquake, Cornwall, January 20th, 1905. 



The shock was of the simple character common, to all slight earth- 

 quakes. It consisted of a single prominent vibration, resembling a 

 thud or blow, accompanied by a brief series of rapid tremors. The 

 estimates of the duration range from 2 to 5 seconds, the average of five 

 estimates being 3^ seconds. 



The sound was heard by all the observers. It was compared to 

 passing waggons, etc., in 27 per cent, of the records, to thunder in 

 42 per cent., to wind in 3, to loads of stones falling in 3, to the fall of 

 a heavy body in 9, to explosions in 12, and to miscellaneous sounds in 

 3 per cent. The beginning of the sound preceded that of the shock in 

 69 per cent, of the records, and coincided with it in 31 per cent. ; the 

 end of the sound preceded that of the shock in 54 per cent, of the 

 records, coincided with it in 38, and followed it in 8 per cent. 



It follows, from the incomplete seismic evidence, that the mean 

 direction of the originating fault is about north-east and south-west, its 



