EARTHQUAKES. 



255 



tions of the solid strata. The intitnate connection between earth- 

 quakes and volcanic agency, is too obvious to require much illustra- 

 tion. All volcanic eruptions -are preceded by earthquakes, of great- 

 er or less extent ; but all earthquakes are not attended by volca- 

 nic eruptions. The elastic vapour may sometimes find vent through 

 existing fissures and apertures ; or, the aqueous vapour may meet 

 with subterranean currents of cold water, and suddenly collapse, pro- 

 ducing a second earthquake in a contrary direction. In common 

 language, the agitation of the ground, when the surface is not brok- 

 en, is called the shock of an earthquake. Since the records of his- 

 tory, there have been no earthquakes in Great Britain equal in inten- 

 sity to what have taken place in the southern parts of Europe. In 

 the year 1247, a general earthquake is said to have extended over 

 England ; it threw down the church of St. Michael's, on the Hill at 

 Glastonbury. The greatest earthquake recorded in England, took 

 place November 14, 1318. On April the 6th, 1580, an earthquake, 

 felt in London and Westminster, threw down a part of St. Paul's 

 church, and of the Temple church. Perhaps, in the present time, 

 ten years seldom elapse without the shock of an earthquake being 

 felt in some part of Great Britain ; but these are too feeble to re- 

 quire historic notice. We have evidence, however, of mighty earth- 

 quakes having shaken the surface of this part of the globe. The 

 faults and dislocations of the strata, of which some account has been 

 given in different parts of the present volume, must have been ac- 

 companied, during their formation, with more violent agitation of the 

 ground than any recorded in history ; but it is probable that, at that 

 period, the land which now forms Great Britain had, only partially, 

 emerged from the ocean. 



Soon after the discovery of .":3 Leyden Phial, many natural phe- 

 nomena were ascribed to electric action, and earthquakes were sup- 

 posed to be the result of electric shocks, acting with great intensity 

 in th6 interior of the earth. The electric theory of earthquakes was 

 soon discarded as untenable ; but now, when the identity of mag- 

 netic and electric agency seems in many respects, to be established, 

 it may deserve consideration, whether an interrupdon to the magnet- 

 ic or electric currents, which circulate through the earth, may not, 

 sometimes, occasion earthquakes, acting almost instantaneously over 

 large portions of the globe. 



If, as some philosophers maintain, there is a central fire under 

 every part of the globe, or if certain spaces only are filled with ig- 

 nited matter, we can scarcely doubt that chemical changes are tak- 

 ing place, which will also change the electrical relations between 

 mineral beds. A series of strata may act like the plates of an im- 

 mense voltaic battery, and discharge the electricity from one inter- 

 nal part of the globe to another, exciting vibrations that may agitate 

 a whole hemisphere. I was informed by a gentleman who resided, 

 several years, near the feet of the Himmahlaya mountains, that peals 



