﻿Vol. 6 1.] TWIN-EARTHQUAKES. 19 



shocks which, during that time, disturbed areas of more than 

 10,000 square miles ; while the four strongest shocks of the last 

 21 years were all twin-earthquakes. Earthquakes of the first 

 magnitude, however, such as the Japanese earthquake of 1891 

 or the Indian earthquake of 1897, are far more complex than twin- 

 earthquakes, both in their nature and origin. 



II. BIBLIOGRAPHY. 



1. Davison, C. ' On the Pembroke Earthquakes of August 1892 & November 1893 ' 



Quart. Journ. Geol. Soc. vol. liii (1897) pp. 157-75. 



2. Davison, C. ' The Hereford Earthquake of December 17th, 1896 ' Birmingham, 



8vo. (1899) ; especially pp. 226-39, 243-45, & 294-95. 



3. Davison, C. ' The Carlisle Earthquakes of July 9th & 11th, 1901 ' Quart. 



Journ. Geol. Soc. vol. lviii (1902) pp. 371-76. 



4. Davison, C. 'The Derby Earthquakes of March 24th & May 3rd, 1903' 



Ibid. vol. lx (1904) pp. 215-32. 



5. Davison, C. ' The Leicester Earthquakes of August 4th, 1893, and June 21st, 



1904' Ibid. vol. lxi (1905) pp. 1-7. 



6. Davison, C. 'The Derby Earthquakes of July 3rd, 1904' Ibid. pp. 8-17. 



7. Dutton, C. E. 'The Charleston Earthquake of August 31st, 1886' U.S. 



Geol. Surv. Ninth Annual Report, for 1887-88 (1889) pp. 209-529, especially 

 pp. 260-64 & 270-320. 



8. Mallet, R. 'The Great Neapolitan Earthquake of 1857, &c.' (1862), espe- 



cially vol. ii, pp. 162-63. 



9. Meldola, R., & White, W. 'Report on the East- Anglian Earthquake of 



April 22nd, 1884 ' (1885), especially pp. 37, 44, & 92-93. [Essex Field-Club 

 Special Mems. vol. i, 1885.] 



10. Mercalli, G. ' II Terremoto Ligure del 23 febbraio 1887 ' Annali dell' 



Uff. Centr. Meteor. & Geodin. ital. ser. 2, vol. viii, pt. iv (1888), especially 

 pp. 567-76. 



11. Mekcalli, G. 'I Terremoti della Calabria meridionale & del Messinese ' 



Memorie di Mat. & di Fis. Soc. ital. Sci. ser. 3, vol. xi (1898), especially 

 pp. 117-21 & 131-39. 



12. Taeamelli, T., & Mercalli, G. ' I Terremoti Andalusi cominciati il 25 di- 



cembre 1884 ' Atti R. Accad. Lincei, Mem. ser. 4, vol. iii (1885-86) pp. 116-222, 

 especially pp. 165-68, 177-80, & 203-10. 



III. Nature of T wiis t -E art h quakes. 

 Wide Area of Observation. 



The wide area over which the twin-shock is felt is perhaps the 

 strongest evidence that the phenomenon is not of local origin. In 

 the Hereford earthquake of 1896, the places where it was felt are 

 distributed almost uniformly over the whole district bounded by 

 the isoseismal 5, or over more than 40,000 square miles. Towards 

 the north-west it was also perceptible in Westmorland, in the 

 Isle of Man, and in Ireland, or very nearly to the boundary of 

 the disturbed area. The twin-shock of the Pembroke earthquake 

 of 1892 was also observed almost to the limits of the disturbed 

 area, from Ehyl to the Scilly Isles, and from Worcester to Tullow 

 in County Carlow. In the Pembroke earthquake of 1893 it 

 was again noticed in nearly all parts of the disturbed area, and at 

 places so near its boundary as Derby, Ashley, and Bournemouth. 

 The twin-shock of the Derby earthquake of 1903 was recorded 



c2 



