18 THE INTERPRETATION OE THE [Feb. I909, 



would be tbe anticlinal fault, and not any of the several overtbrusts 

 which run parallel to it, and this was the one which seemed to 

 correspond with the focal line of the Leicester earthquake. 



Prof. Cole asked whether the Author was prepared to locate the 

 origin of large earthquakes at a far greater depth in tbe crust than 

 Mallet would have proposed. It seemed possible that what were called 

 lines of weakness in the earth's crust, along which movements 

 of the surface might take place, represented lines of weakness in those 

 inaccessible regions that Dr. Ampferer had called the untergrund. 

 Our surface-movements might thus, as Ampferer had urged, have 

 no relation to the characters or disposition of the rock-masses 

 visible to us, but might, unhappily for geological reasoning, depend 

 on those of more active masses entirely beyond our reach. 



Mr. J. F. N. Green said that it had been shown that the sug- 

 gested distribution of stresses was competent to produce a displace- 

 ment along the line of fault. Such a displacement must necessarily 

 produce vibration, which accounted in any case for at least part 

 of the earthquake, which part might be said to be caused by the 

 fault. He enquired whether there was any evidence that a part of 

 the earthquake remained which could not thus be accounted for. 



The Rev. E. C. Spicer asked the Author whether he had arrived 

 at any conclusion with regard to the origin of the forces that pro- 

 duced a series of couples acting horizontally in the earth's crust 

 and producing apparently a ' flaw ' rather than a fault. 



M. M. Allorge, referring to a stay which he had made in 

 California two years before the earthquake of 1906, said that, 

 although he was unable to investigate the nature of the unter- 

 grund, he had nevertheless been impressed by some structural 

 features which tallied very well with the Author's ingenious ex- 

 planation of recent events. Already at that time the San Andreas 

 fault, along which considerable displacement was to take place two 

 years later, gave rise to unusual features in the topography. Along 

 that ' earthquake-crack,' cutting the coastal ranges obliquely, there 

 were series of low passes, of elongated basins, some of which had 

 reversed slopes or even no outlets. The recent seism had thrown 

 light on the genesis of all these unsystematic topographical 

 features, which might be accounted for by a truncation and a lateral 

 displacement of the drainage-system. 



The second point that impressed the speaker was the evidence 

 afforded by physiography of the recent and possibly present forma- 

 tion of newer folds off the coast of California. The city of Los 

 Angeles was as much exposed to earthquakes as San Francisco. 

 On a line running south-south-west of Los Angeles was the rocky 

 promontory of San Pedro, formerly an island and now connected 

 with the mainland by a succession of elevated beaches. The island 

 of Santa Catalina, 25 miles off San Pedro, was a maturely dissected 

 sierra, the summit of which alone stood above the waters of the 

 Pacific ; submerged valleys and short rios presupposed a recent sub- 

 sidence. Some 30 miles to the south-south-west lay another island 

 (San Clemente), exhibiting a terraced profile with raised beaches. 



