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214 



EARTHQUAKE PHENOMENA. 



[Sect. VII 



has 



observer should remark if its direction of motion 

 appeared to change as it passed along, and obtain decisive 

 evidence of its actual transit, for sometimes the 



leave 



imultaneously 



of country, where the origin is deep-seated, and nearly 

 veiiically below. Changes in the rate of transit hori- 

 zontally, or in the force of the wave, should be noted by 

 its effects on similar objects at distant spots. These 

 changes m.ay be expected at the lines of junction of dif- 

 ferent rocks or other formations. Evidence should also, 

 if possible, be got of any breaking up of the primary 



felt 



wave into 



where only one has occurred further back. 



All evidence should, as far as possible, be circumstantial 

 Nature rightly questioned never lies ; but men ai-e prone 

 to exaggerate, at the very least, where novel and startling 

 events are in question. 



Various local conditions must be recorded : — the nature 

 of the geological formations at the spot, not merely the 

 underlying rock, with the directions of its bedding, lami- 

 nation, joints, &c. ; but the character of surface, the depth 



and description, of its loose materials, their variations and 

 extent, tlie geological formations of the surrounding dis- 

 tricts from whence and towards which the earth-wave 

 travels especially. The deeper a knowledge can be got 

 by exposed sections, &c. of the rocks of the shaken district 

 the better, the proximity or otherwise to volcanic vents, 

 active or paa?ive, the character of surface of the country 

 shaken, mountain or plain, even or liroken, solid or fis- 

 sured ; if the latter, their general directions, dip, &c., 

 whether dry or flooded, and the effects on the elements of 



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