390 Geological Society : — 



of the impulse within the same or an overlapping focus. They must 

 therefore be due to impulses in two detached, or practically detached, 

 foci ; and it is shown that all the known phenomena of twin- 

 earthquakes can be thus accounted for. 



In British twin- earthquakes, the distance between the epicentres 

 varies from 4 to 23 miles, the average for seven recent earthquakes 

 being between 10 and 11 miles. As a rule, the foci are elongated 

 approximately in the direction of the line joining them, showing 

 that they are portions of the same fault. The foci appear to be 

 situated at different depths, and, in two cases, the fault probably 

 changes hade in the region between them. 



The existence of the synkinetic band and the brevity of the 

 interval between the two parts of the shock, show that, when the 

 impulses are not absolutely simultaneous, the second takes place as 

 a rule before the vibrations from the first focus have time to reach 

 the other. Thus, twin-earthquakes are due to a single generative 

 effort ; and they are caused, it is urged, by the growth of a crust- 

 fold cut transversely by a fault. If the movement is such that the 

 anticline of the fold is made more anticlinal and the syncline more 

 synclinal, the middle limb will remain practically undisturbed ; so 

 that, by a single effort, there will be two impulses in detached foci 

 situated at different depths. The average distance between suc- 

 cessive anticlines and synclines in France along several lines lies 

 between 9 and 12 miles, which agrees closely with the average 

 distance between the epicentres of twin-earthquakes. 



January 4th, 1905.— J. E. Marr, Sc.D., F.R.S., President, 

 in the Chair. 



The following communications were read : — 



1. 'The Marine Beds in the Coal-Measures of North Stafford- 

 shire.' By John T. Stobbs, Esq., E.G.S. 



2. ' The Geology of Cyprus.' By Charles Yincent Bellamy, 

 M.Inst.C.E., E.G.S. With Contributions by Alfred John Jukes- 

 Browne, B.A., F.G.S. 



The following are the chief formations described : — 



Pleistocene. { ® an( * y ^eatones. lupto 50 feet. 



[ Sands and conglomerates. J I 



Pliocene. j She11 ^ ^stones with calcareous j m tQ UQ feet 

 a. ui^ y sands and sandstones. J 



Break. Intrusion of igneous rocks. 



('"White chalky limestones and marly 1 



T I chalks, with layers and nodules of \ About 1000 feet. 



1DALIAN ^ flint> J 



(Uligocenej. j Gre ^ an(] yellowish mar i S) with beds 1 40Q ftet 



L °f gypsum. J 



KytiirjEAN f Grey felspathic sandstones and } ,, -^qq ^^ 

 (Upper Eocene), l sandy shales. J 



Break, 

 m , I Grey limestones and dolomites ; ] 



Irypanian I white and - k n)arbl both L Possibly 6000 feet, 

 (? Crktaceous). . j f - , j 



v '- . ' I massive and laminated. J 



