EARTHQUAKES. 



623 



the mountain, as in the case of the commencement of the catastrophe of 

 A.D. 79, when the whole side of Vesuvius was torn away, and continuous 

 showers of ashes fell for days and nights, burying everything, while the hot 

 lava poured down the sides. Stones and ashes with vapours are hurled into 

 the air. Clouds of steam are formed, and vivid electrical discharges take 

 place in these clouds, while water dashes down, carrying stones (" volcanic 

 bombs"), and reflected lurid flames from within are cast on the steaming 

 clouds, which look like fiery columns. Then the lava issues in a white, hot, 

 steady, irresistible stream, covering everything, and burning up all vegetation. 



New volcanoes are continually in process of formation, and at Santorin 

 for hun- 

 dreds of 

 years 

 volcanic 

 action 

 has been 

 busy in 

 for m i n g 

 islands. 

 These 

 vio lent 

 efforts of 

 Nat u re 

 frequent- 

 ly give 

 rise to 

 earth- 

 quakes, 

 which 



are the most destructive of natural 

 convulsions. The records of late oc- 

 currences are fresh in the minds of 

 all readers, and need not be specified. 

 The slow subsidence and gradual rig. 7 io. Birth of a volcano, 



upheaval of the land is still going on, but we are frequently startled by the 

 account of a rupture of the ground or the destruction of a portion of a city. 



The motion of the earthquake is generally in a direct line, and undu- 

 lating. Sometimes what are termed vertical shocks arise and destroy solidly- 

 built edifices. Mountains have been overturned by earthquake shocks, and 

 trees have been twisted round. Sometimes the ground yawns into enormous 

 fissures. The sea is tossed into great waves and encroaches upon the land, 

 and when the sea recedes the recession of the water is followed by a more 

 terrible invading wave sweeping all before it. Earth tremblings often occur 

 far away from volcanoes, and without any visible connection with volcanic 

 action. There are many aspects of land and water which the student of 



