192 On EartJiqiiaJccs* 



Rioliamba in 1797, which Hnmboklt describes as "one of the most fearful 

 recorded in the physical history of our planet," was not accompanied by any 

 iioise whatever. In other instances, the explosion is heard after the shock, 

 and often the sounds are heard without the shaking: of the earth. " The 

 nature of the noise, " says Humboldt, varies also very much, being either 

 rolling or rustling, or clanking like chains when moved, or like near thunder ; 

 or lastly, clear and ringing as if obsidian or some other vitrified masses were 

 Gtruck in subterranean cavities. As solid bodies are excellent conductors of 

 sound, which is propagated in burnt clay, for instance, ten or twelve times 

 quicker than in air, the subterranean noise may be heard at a great distance 

 from the place where it originated."- Thus in 18112 a tremendously loud 

 noise resembling thunder, was heard over a space of 9,200 square miles in 

 South America, unaccompanied by an earthquake, whilst at the distance of 

 632 miles to the northeast the volcano of vSt. Yincent in the lesser Antilles, 

 poured forth a stream of lava. In 1742, on the great eruption of Cotopaxi, 

 subterranean sounds resembling the discharges of cannon were heard at 

 Hcnda, 436 miles distant. Although the precise natm-e of those causes which 

 occasion earthquakes remains unknown, yet, by careful observation, many 

 particulars concerning the direction, rate of travelling, and variations in the 

 force of the vibrations appear to have been ascertained. If a stone be thrown 

 into a pond of still water, the small waves produced will roll away in all direc- 

 tions in gradually increasing circles — becoming more feeble as they recede from 

 the centre. The vibrations of an earthquake seem to originate from a shock 

 given at one point and to travel away in the manner of the weaves of water 

 put in motion by the stone, but with much greater velocity. Dm-ing the 

 great earthquake at Lisbon, its waves spread across the earth's surface at 

 the rate of twenty miles in a minute between the time the first shock was 

 felt at Lisbon and its occurrence at other places. This velocity is greater 

 than that of a cannon ball, and we may well imagine that the efiects when 

 passing under stoiie buildings would be of a violent character. Should the 

 undulation be vertical, then the houses would be shaken upwards, but if 

 horizontal, then their foundations would be jerked from beneath them. Were 

 a number of light objects to be placed upon a table, and a smart blow with 

 a hammer given to one end of the leaf, the vibrations would be lateral ; but 

 if the blow were given to the under side of the table, vertical. The articles 

 upon the table Vi'ould be shaken horizontally or vertically, according to the 

 direction of the blow. All the shocks of earthquakes appear to be this 

 experiment performed upon a large scale, the crust of the earth being the 

 leaf of the table, and the cities representing the small objects upon it. The 

 great and unanswered question is, whence does the original concussion which 

 produces the tremblings proceed. Upon this point there are many theories. 

 The one in which we believe is that all the effects of earthquakes are conse- 

 quences of the sudden rending of the earth's interior crust. Beneath all 

 Canada, and all the world beside, the crust of the earth, as all Geologists are 

 aware, consists of a floor of solid rock. There is a little loose soil, a 

 quantity small indeed, when compared to the bulk of the globe, strewn over 



