258 EARTHQUAKES IN NORTH CAROLINA. 



sounds. A person, therefore, standing ii thousand yards from a quarry 

 feels the trembling of the earth some time before he hears the sound of 

 the blast. But in all these convulsions of the mountain the concurrent 

 testimony is that the sounds and shocks arc either simultaneous or 

 nearly so. The blasting of rock, therefore, cannot account for this im- 

 j)ortant fact. 



Another hypothesis is, that these effects may be the result of elec- 

 tricity escaping from the mountain to the cloud, or descending from the 

 cloud to the mountain. There is nothing in the known operations of 

 electricity to produce effects of this kind. Furthermore, these sounds 

 and shocks occur as often in fair as foul weather; and the sounds are 

 altogether different, as we had an opportunity of comparing them during 

 our lirst night's stay ujjou the mountain. Electricity never explodes 

 unless it meets with a bad conductor, and as the mountain affords it 

 an easy transit, the explosion must take place somewhere between the 

 summit and the cloud, or along the line of its pathway. The explo- 

 sion, therefore, being in the air, must be subject to the same laws of 

 sound as the blast of the quarry, and the same method of reasoning 

 will apply in this case as in the other. 



The simultaneousness of the shocks and explosions proves that the 

 sound has not far to travel through the air to reach the observer; and 

 while the primary cause of the explosions may be deeply seated in the 

 earth, yet the immediate cause of the sounds may be at or near the sur- 

 face. It is known that the loudness and intensity of sounds depend 

 upon tlie amplitude of the sound-wave. Suppose, then, that the cause 

 of these explosions be deeply seated in the crust of the earth, the force 

 acting and reacting upon the superincumbent strata will impart its 

 vibrations to them and transmit through them its impulsions to the 

 atmosphere above.* I am inclined, therefore, to the opinion that most 

 of the noises accompanying earthquakes are the results of vibratory 

 movements in the earth's crust, or are the secondary effects of a force 

 acting at great depths beneath. This opinion seems to be sustained by 

 the evidence of the witnesses upon the summit as well as five miles 

 from the base of Stone Mountain, all of whom concur as to the simul- 

 taneousness of the shocks and explosions. To this it may be objected 

 that earthquake-shocks are often unaccompanied with noises, or that 

 the former may precede the latter by several minutes. In reply, I will 

 state that the crust of the earth is composed of different strata, some 

 capable of transmitting vibrations that are audible and others that are 

 not, as a string may be made to vibrate and yet produce no audible 

 sound. iSTow, suppose our observer to be standing upon a section of the 

 earth's crust which is incapable of receiving or imparting sound-vibra- 



* This explanation is undoubtedly correct ; the velocity of the sound-wave in the earth is 

 the same as that of the wave of percussion ; or, in other words, the two are identical. An 

 car, therefore, placed at the surface of the ground would at any point hear a sound simul- 

 taneously with the shock. J. H. 



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