1872.] OLDHAM AND MALLET CACHAE EARTHQITAKE. 261 



produced the marvellous tale of the great earthquake at Kingston, 

 Jamaica, of 1692, when, if we helieve the narratives, such fissures, 

 suddenly opening across the streets, swallowed up people and cast 

 them out again, or hit them in two as they closed again. 



It is the foundation too of the hazy yet most exaggerated accounts 

 given by the Eoyal Commissioners in their report upon the great 

 Calahrian earthquake of the last century (1783), in which the 

 voragines, as they call these fissures, and the " mud-erui^tious " 

 coming from them, play a part equally marvellous and unintelligible. 



The writer was himself the first to announce his conviction, based* 

 on the necessary consequences of knowing the true nature of the 

 earthquake wave-movement, that any direct production of earth- 

 rents or fissures by the movement of the wave-particle or by the transit 

 of the wave was physically impossible, and that their occurrence 

 must be otherwise accounted for (first "Report on the Facts of Earth- 

 quakes," Brit. Assoc. Eeports, 1850). It was not, however, until after 

 he had been enabled to examine minutely the circumstances and 

 adjuncts of such fissures, both small and lai-ge, produced in the 

 great Neapolitan earthquake of 1857, that he was able positively to 

 sustain his previsions by comparison with the facts in nature. The 

 conclusions at which he arrived do not appear, however, to have struck 

 geologists universally with sufficient force to put an end to the old 

 and no longer tenable notion which still disfigures unchallenged the 

 pages of some systematic works. 



And as a misconception as to this matter is almost tantamount to 

 having no clear notion at all of the true nature of earthquake- 

 movement. Dr. Oldham's observations are of special importance, the 

 fissures in this case being of first-class magnitude and having con- 

 comitants of a very instructive character, while the modus operandi 

 of their production once grasped can never again be misunderstood. 



Por the more complete statement of the conditions of production 

 of earthquake fissures and of certain of the phenomena which mav 

 attend their production, such as the fire and smoke supposed occa- 

 sionally to ascend from them, the welling up from them of water 

 or mud &c., the writer may refer to his first " Report on the Facts 

 of Earthquakes," §§ 4, 5, and 6, et passim (Brit. Assoc. Reports, 

 1850), and to his ' Report on the Neapolitan Earthquake,' vol. ii., 

 and will here confine himself to calling the recollection of the Fellows 

 present to the leading facts of the case. The production of every 

 earth-fissure by earthquake-shock is only a case of more or less 

 complete landslip, induced by the circumstances of the shock ; and 

 it is the necessary condition of the production of a fissure thus 

 brought about that, of the earth-masses at either side of the fissure 

 when formed, one or other shall have been, relatively to tlie other, free 

 in one direction — and generally that the mass moved which gives 



* It is upon the same radically incorrect conception that the notions 

 of the Messrs. Eogers as to the production of the Appalachian chains of moun- 

 tains are based — when tliey attribute their wave-like form of transverse section 

 to the translation of great earth-billows petrified, as it were, in their course — 

 R. M., July 4, 1872. 



