1890.] On the British Earthquakes of 1889. 277 



a direction about N. 30 E. to S. 30 W. ; it is about 25 miles long 

 and 18 miles broad, and about 350 square miles in area. The sound- 

 area appears to be coextensive with the disturbed area, but the 

 observations are too few in number to prove this. The epicentrum 

 is about 3 miles south-east of Clachan. Dr. Lapworth, in a note to 

 the author, describes briefly the geological structure of the disturbed 

 area, and remarks that its longer axis coincides in direction with the 

 theoretical position of the southern zone of contrary movement in 

 that district. 



5. East Cornwall Earthquake, October 7. About 13 h. 45 m. 

 Intensity IV. The disturbed area is elliptical in form, 25 miles long 

 and 20 miles broad, the longer axis running east and west, and about 

 400 square miles in area. The nature of the shock varied somewhat 

 throughout the disturbed area, but its intensity was very nearly 

 constant. Near the centre of the area the earthquake-sounds were 

 the most prominent feature, but towards the boundary these died out. 

 The sound-area may, however, have been coextensive with the 

 disturbed area, and it is probable that the sound-focus is nearer the 

 surface than the seismic focus. The epiceutrum is at a point about 

 2| miles south-west of Altarnon, which is not far from the centre of 

 the great granite boss of eastern Cornwall. The longer axis of the 

 disturbed area is also parallel to the axis of folding of the district. 



Doubtful Earthquakes. Two shocks, supposed to be those of earth- 

 quakes, are briefly described, but the evidence is insufficient to prove 

 their seismic origin: (1) Little Rhondda Valley (S. Wales), 

 June 22, about 22 h. 30 m. ; (2) Lyme Regis, July 5, between 

 23 h. and 23 h. 15 m. The former of these may possibly have been 

 caused by subsidences of the rock over worked-out portions of the 

 coal mines. 



In conclusion, the differences between British and Swiss earth- 

 quakes are pointed out. The former are rare, and their disturbed 

 areas more or less circular, indicating short fault-slips ; the latter 

 are frequent, and their disturbed areas elongated, their axes being 

 parallel to those of the neighbouring mountain ranges, and the fault- 

 slips correspondingly long. They are witnesses respectively of com- 

 paratively late and early stages in the process of mountain evolution. 



