EARTHQUAKE PHENOMENA. 427 



there be somo free from any, and their local conditions, to be par- 

 ticularly noted. 



Referring now to secondary phenomena, or effects resulting from the 

 transit of the earth-wave, (other than merely measures of it,) we 

 should observe falls of rock, or land -slips, to which most of the con- 

 ditions of shattered buildings apply. Land-slips change their initial 

 directions frequently, in consequence of moving over curved or 

 twisted surface of rocks; thus the previously straight furrows of a 

 field may be found twisted after an earthquake. Scratches or furrows 

 engraven on rocky surfaces by such land-slips should be looked for. 



Sometimes great sea- waves are produced by the fall into the sea of 

 rock or land-slips, which need to be carefully distinguished from the 

 true great sea-wave produced by an original impulse of the sea- 

 bottom. Land-slips often dam rivers, fill up lakes; and various 

 changes of surface again produce basins for new lakes, to be filled 

 by the changed river-courses. The circumstances, as far as possible, 

 should be accurately observed, and the causation of the events 

 unwound, and all such phenomena cautiously separated from actual 

 ejections of water, (temperature to be ascertained,) which are said 

 sometimes to have happened on an immense scale. — (Humboldt, Per- 

 sonal Narrative; " Cosmos," vol. iv.) 



Fissures containing water often spout it up at the moment of shock. 

 Wells alter their water-level, and sometimes the nature of their con- 

 tents; springs become altered in the volume of water they deliver. 

 The directions of the fissures, and the relations of such directions to 

 that of the shock, should be ascertained, and any changes in the 

 temperature of wells noted. Ejections from holes or fissures of 

 strange liquid or solid matters, sometimes of dry ashes or dust, are 

 recorded, and occasionally fiery eructations or smoke are said to have 

 occurred, especially near volcanic centres, and blasts of steam vapors 

 or gases, whose chemical characters should be in all the above cases 

 observed as far as possible. The dust of overthrown buildings, or 

 that produced by the. rending of rocky or other masses, must not be 

 confounded with these. Fissures, sometimes of profound depth, open 

 and remain so, or close again; their directions, dimensions, time and 

 order of production, and closing up, and the formations in which they 

 occur, to be noted; bodies engulfed to be detailed as future organic 

 remains. Fissures in solid rock arise either from the effects of inertia 

 or from the range of molecular displacement of the passing wave 

 exceeding the elastic limit of the materials disturbed; but fissures in 

 earth or other discontinuous and very imperfectly elastic masses seem 

 due only to the secondary effects of the shock, producing land-slips, 

 subsidations, &c. — (See "First Report on Facts of Earthquakes," 

 sec. 6, Secondary Effects.) Permanent elevations and depressions of 

 the land usually accompany earthquakes, and are of much importance 

 to science, but, as already remarked, must be viewed as clearly 

 distinct, from the earthquake itself. Such elevations or depressions 

 have a common cause with the earthquake; both are clue to the 

 volcanic efforts beneath, but are not the less absolutely distinct 

 phenomena, to confound which is to lose sight of all true science in 



