298 Dr. C. Davison— Brit i-^/, Earthquakes. 



300 square miles in area, its centre being 9 miles west of Dunoon. 

 The latter is 36 miles long, 21 miles wide, and 564 square miles in 

 area, the direction of its longer axis being E. 40^ N. The distance 

 between the two curves is 2*1 miles towards the south-east and 

 3'7 miles towards the north-west. 



The shock consisted of a continuous series of tremors, lasting on an 

 average of 2^ seconds, and gaining in strength towards the close. 



The sound was heaixl by all of the observers, and was compared in 

 38 per cent, of the records to passing waggons, etc., in 31 per cent, to 

 thunder, in 6 to wind, in 5 to the fall of loads of stone, in 2 to the fall 

 of a heavy body, in 17 to explosions, and in 2 per cent, to miscellaneous 

 sounds. The beginning of the sound preceded that of the shock in 

 71 per cent, of the records, coincided with it in 23, and followed it in 

 6 per cent. ; while the end of the sound preceded that of the shock 

 in 21 per cent, of the records, coincided with it in 28, and followed it 

 in 52 per cent. The duration of the sound was greater than that of 

 the shock in 89 per cent, of the records, and equal to it in 11 j^er cent. 



So far as we can judge from the seismic evidence, the mean direction 

 of the originating fault is about E. 40° N., and its hade towards the 

 north-west. Several of the faults laid down on the Survey map have 

 approximately this direction, but I do not feel that the elements are 

 determined with sufficient accuracy to justify its connection with any 

 particular fault. 



2. BcddgeJert Earthquahe : October 2lst, 1904. — Time of occurrence, 

 about 6.5 a.m. ; intensity, 4 ; number of records 5, from 4 places. 



I am indebted to Mr. E. Greenly and Mr. J. 11. Dakyns for all the 

 records of this earthquake, which seems to have been chiefly perceptible 

 in the district lying to the south of Snowdon. The shock was felt at 

 Blaenau Ffestiniog, Plas Gwynant, and Croesor, the last two places being 

 respectively 3 miles north-east and 4 miles south-east of Beddgelert. 

 The shock was accompanied by a noise somewhat like thunder at these 

 places and also at Eeddgelert. Thus the earthquake was perceptible 

 over a district measuring at least 7 miles from east to west and 

 3 J miles from north to south. 



3. St. Agnes Harth quake : Jan. 20tli, 1905. — Time of occurrence, 

 1.50 a.m. ; intensity, 5 ; centre of isoseismal 4, in about lat. 50° 22' N., 

 long. 5° 18' W. ; number of records 44, from 24 places, and negative 

 records from 9 places. (Fig. 1.) 



Most British earthquakes are connected with foci, which lie beneath 

 the land-area of the country. A few, however, are due to displace- 

 ments that are partly or entirely submarine. The epicentres of the 

 Pembroke earthquake of August 18th, 1892, and the Carnarvon 

 earthquake of June 19th, 1903, appear to have been in part beneath 

 the sea. On March 3rd, 1904, a submarine earthquake occurred in 

 the neighbourhood of Penzance, and this was followed within less 

 than a year by another, with its epicentre on the opposite side of the 

 Cornish peninsula, and distant not more than 22 miles from that of 

 the Penzance earthquake. 



As will be seen from the accompanying map (Fig. 1), only portions 

 of the isoseismals 5 and 4 can be drawn, and from their form it 

 is evident that the epicentre is situated several miles from land. 



