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,^^r> »♦ Cor 



HERTFORDSHIRE EARTHQUAKES. 



By John Hopkinson, F.L.S., F.G.S., F.Z.S., F. E. Met. Soc, 

 Assoc. Inst. C. E. 



Mead at Watford, 29th Jamianj, 1907. 



I. Introduction. 



Owing to the disastrous earthquakes which have recently 

 taken place in Columbia, California, and Chili, all within the 

 first eight months of last year, and all on the west coast of 

 America, such catastrophes, and the phenomena attendant 

 upon them, have lately excited so much interest that I thoiight 

 this might be an appropriate time to bring before our Society 

 the records which I have been able to find of earthquakes which 

 have occurred in Hertfordshire. Moreover, during the present 

 month not only have two other great earthquakes occurred — one 

 in Jamaica reducing to ruins its capital, Kingston, and the other 

 in Sumatra nearly annihilating the island of Simalu, both being 

 attended by great loss of life — but seismic disturbances are 

 taking place in all parts of the world, including our own 

 country, for earthqiiakes have occurred within the month at 

 Newport in Monmouthshire and at Oban in Argyllshire. 



" Earthquakes have been properly distinguished into natural 

 and supernatural," said an early writer.* This classification 

 would not be accepted in the present day, for we now endeavour 

 to find a physical cause for all phenomena which occur in the 

 universe. The origin of earthquakes has for long engaged the 

 attention of scientific men, and those who have lately given the 

 subject the most careful attention are in fair agreement as to 

 the origin of nearly all being from one of three causes — (1) the 

 faulting of strata or slipping of rock-masses one over the other 

 from the contraction of the earth owing to the loss of its 

 internal heat ; (2) the formation of hollow spaces either from 

 chemical disintegration of rock as by the solvent action of water 

 in limestone districts or from the ejection of ashes and lava by 

 volcanic eruptions, and the subsequent falling-in of the super- 

 incmxibent strata ; and (3) explosion of steam from the 

 admission of water into highly-heated portions of the earth's 

 interior by gradual percolation, or through fissures in the bed of 

 the ocean. All possible causes are not exhausted by these three, 

 for there is one other at least, which, although at one period 

 frequently advanced, appears lately to have been ignored, and 

 that is a discharge of electricity, as in the " return-shock " from 

 the earth to the atmosphere. The question as to whether 



* Rev. A. Bruce : ' Au Historical Account of the most remarkable Earthquakes 

 and Volcanic Eruptions,' p. 4 (1797). 



VOL. XIII. — PART in. 11 



