Ixvi PROCEEDINGS OF THE GEOLOGICAL SOCIETY- [YoI. Ixxviii^ 



from thd great earthquakes which have been studied in detail. 

 Reference has akeady been made to the Californian earthquake 

 of 1906, and the conckision drawn in that case is more fully 

 exemphfied by the Indian earthquake of 1S97. Here thei-e was no 

 single leading fault and zone of maximum intensity of shock, but a 

 complicated network of lines of extreme desti-uetiveness, ramifying 

 over an area not much different fi-om that of England, and ex- 

 tending light across a series of great tectonic features, across the 

 great monocline of the southern face of the Assam range, across 

 that range itself, across the aUuvial plain of the Bralunaputra 

 Talley, the great boundary -faults of the Himalayas, and probably 

 even across the main axis of elevation of the range. 



A still more instructive instance is the Charleston earthquake 

 of 1SS6. Here, in a region as devoid of any great structural 

 feature; either of folding or faulting, and as lirtle subject to earth- 

 quakes, as could be found in our own country, there suddenly 

 occurred a great earthquake, of destmctive violence in the central 

 area and felt over an area measuring about 1500 miles across. It 

 was an earthquake of first-class magnitude, whether we regard the 

 maximum violence of shock or the extent of area affected, yet 

 there is nothins: in the structure of the surface-rocks to su^^est 

 that its origin was due to any tectonic process, and equally 

 nothing which could lead to its classification as volcanic ; and. 

 if we accept the conclusions of Col. Harboe, regarding the 

 character and extent of earthquake origins, the absence of any 

 connexion, between the origin of the earthquake and the tectonics 

 of the surface-iiDcks, becomes absolute, for, according to this 

 interpretation, the origin becomes almost co-extensive with the 

 seismic area, and the diminution of violence in the outer portions 

 is not solely due to enfeeblement, resulting from the elasrie propa- 

 gation of the earthquake wave, but very largely to a diminurion 

 in magnitude of the originating impulse. 



Whether this explanation be accepted or not, it must be conceded 

 that, as regards the two earthquakes pai-ticularly refeiTcd to, of 

 Charleston in 1SS6 and India in 1^97, Col. Harboe's conclusions 

 are not only supported by the particular facts on which they were 

 based, but are in berter accord with a number of peculiarities in 

 the local variation of violence of the shock, and of other phenomena 

 recorded, than is the current notion of a central focus of compai-a- 

 tively restricted dimensions. It accords also with those great 

 earthquakes which, like the Calabrian earthquakes of the present 

 century, had more than one centre of maximum intensity', con- 

 nected by resrions of less violence of shock. 



