Dr. C. Davison—British Earthquakes. 411 
The earthquakes of the last twenty-one years have been in no 
respect unusual. None has exhibited in its central area so destructive 
an intensity as the Colchester earthquake of 1884. Nor has any 
borne a train of after-shocks so numerous as that of the Comrie 
earthquake of 1839. Three earthquakes (those of Hereford in 1896, 
Inverness in 1901, and Swansea in 1906) were, however, strong 
enough to cause considerable damage to buildings; and, in the low- 
lying country on the south side of the Ochil Hills, there have been 
many slight shocks which in their nature and frequency approximate 
towards those which have made the name of Comrie famous. 
Several of the more important seismic centres in this country have 
lain dormant or nearly so during these years. Rumbling noises, 
apparently underground, are said to have been heard in West Mersea 
Island, off the coast of Essex, and, if seismic, may possibly be 
connected with the centre which gave rise to the Colchester earth- 
quake twenty-six years ago. The Comrie focus is represented by 
three slight shocks, and seems to have relapsed into that state of 
quiescence which may precede another outburst of energy. On the 
other hand, the important focus in the neighbourhood of Inverness has 
been unusually active, and other well-known foci have exhibited those 
signs of flickering vitality which from time to time interrupt the 
monotony of our geological existence. 
Hardly any part of Great Britain has been entirely free from the 
transitory effects of earthquake shocks, the only districts left 
undisturbed being the greater part of Durham and Northumberland 
and some of the southern counties of Scotland. 
FREQUENCY. 
Taking into account only those earthquakes recorded by more than 
one observer, the total number which have occurred in Great Britain 
during the interval considered is 250, the greatest numbers in any 
single year being 25 in 1890, 23 in 1901 and 1906, and 20 in 1892, 
and the least numbers being 1 in 1897 and 1899, and 2 in 1895 and 
1902. Of the total number, 50 (including two with submarine 
origins off the coasts of Cornwall) originated in England, 27 in 
Wales, and 173 in Scotland. Thus, on an average, one earthquake 
occurs in Great Britain every month. Also, out of every 20 earth- 
quakes, 4 occur in England, 2 in Wales, and 14 in Scotland; or, 
taking area into account, 2 occur in England, 7 in Wales, and 11 in 
Scotland. 
IntTEeNsITY AND DisturBED AREA. 
Of the 250 earthquakes, 3 were of intensity 8 of the Rossi- 
Forel scale, 9 of intensity 7, 7 of intensity 6, 29 of intensity 5, 64 
of intensity 4, 127 of intensity 3 or about 3, while 11 were merely 
earth-sounds unaccompanied by any perceptible tremor. In Japan, 
220 of the shocks would be described as weak, 16 as strong, and 3 as 
violent; in Italy, 127 would be considered slight, 64 moderate, 36 
strong, and 12 very strong. 
