Earthquakes and Volcanoes 



particles of boracic acid which are used in the 

 preparation of borax. 



Most of the phenomena just described are 

 probably to be regarded as representing the 

 lingering remains of volcanic activity. When 

 a volcano has become extinct, the effects of 

 subterranean heat in the locality may still mani- 

 fest themselves in a subdued form, in such phe- 

 nomena as those of hot springs. Many volcanoes, 

 however, which appear at the present day to be 

 perfectly quiet, are merely dormant, and may 

 break forth with renewed activity at any mo- 

 ment. The early history of Vesuvius, as already 

 pointed out, shows that a volcano, after being 

 silent for ages, may suddenly start forth into 

 fresh life. 



There are few better examples of an area in 

 which volcanic action must have been rife on an 

 enormous scale at a comparatively recent time, 

 than that furnished by the Auvergne and the 

 neighbouring districts in Central France. There 

 the traveller may see hundreds of volcanic cones, 

 known locally as "puys, " still preserving their 

 characteristic shape, in spite of long exposure; 

 there, too, are the streams of lava just as they 

 flowed from the craters, or burst through the 

 sides of the cones (Fig. 52), whilst thick sheets 

 of old lava and beds of ash are spread far and 

 wide over the surrounding country. The dis- 

 trict known as the Eifel, on the west bank of the 

 Rhine, between Bonn and Andernach, offers 

 equally striking examples of extinct volcanoes. 

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