GEOLOGY. 225 



which we hare authentic records, when the bodies of many of the 

 inhabitants were thrown upon a hillside several hundred feet at the 

 other side of the river, the greatest velocity of the shock on that oc- 

 casion did not exceed eighty feet per second. This Mr. Mallet considers 

 to be the maximum force at present possible upon our earth ; it is near- 

 ly as" great as that with which the body of a man falling from the top 

 of the Duke of York's Column would strike the pavement. 



The latter portion of Mr. Mallet's work is occupied by discussing the 

 curious and mysterious phenomenon attaching to earthquakes, called 

 their secular motion. Humboldt pointed out long ago that the mighty 

 seismic force which periodically desolates vast districts in South Amer- 

 ica is continually changing position ; and it is equally certain that the 

 centre of seismic intensity is not constant in the Italian peninsula. 

 Since the last century it has continued to move steadily northward of 

 Calabria, and in Sicily it is moving westward : 



" These facts distinctly point toward some great conclusions. They 

 indicate that the same forces, whatever they may be, that develop 

 themselves as volcanic Agents and as earthquakes, are operative every- 

 where along the lines of the seismic bands, that is to say, along the 

 axial lines of nearly all the great mountain-ranges upon our globe, 

 but that the intensity of these forces is greater by much at some points 

 along these axial lines than at others ; that the intensity remains con- 

 stant nowhere, but shows itself paramount at certain points for immense 

 periods of historic time ; that it wanes and again waxes powerful at the 

 same point (Vesuvius in volcanoes, Antioch in earthquakes, for exam- 

 ple, both long in repose, again long in intense action) ; and that the 

 points of greatest intensity at any given time have been found to shift 

 along the axial lines, now most active here, then further on, but slowly 

 moving, and in the same direction (or expanding in both directions, as 

 Humboldt says of the New Madrid band), in the same cycle of time. 

 Can we possibly, with these facts before us, rest in the commonly-re- 

 ceived vague notion that volcanic and seismic action have their com- 

 mon origin in an all-pervading and perfectly uniformly-distributed 

 planetary temperature, increasing everywhere alike by a uniform hy- 

 pogeal increment '? Can we remain satisfied with the pompous but al- 

 most empty phrase, although sanctioned by a Humboldt, , that 'they 

 are due to the reaction of the interior of our planet upon its exterior,' 

 if the only meaning that we are to attach to the phrase is that the re- 

 action is that of a universal ocean of heated or of molten matter, every- 



/ 



where to be reached within some certain limit of depth ? Do not the 

 facts rather all point toward some cause that has been long present, 

 and is so now, and still in action wherever mountain-ranges have been 

 elevated, as well as wherever volcanic vents are thrown or are throw- 

 ing up their lines of cones, but whose nature must be such as is called 

 locally and spasmodically into action, now most energetically at one 

 point, now at another of the same line, but yet is never exhausted at 

 any ? The discovery of the real nature of this cause will be the key to 

 all true knowledge, both of volcanic action, which is only its symptom, 

 and of all the forces that have produced and do produce the elevations, 

 or, to speak more correctly, the changes of level of the surface of our 

 own and that of other planets. Earthquakes, then, demand to be re- 

 garded not as themselves agents of permanent elevation of the land, 



