xil] earthquakes AND VOLCANOES. 203 



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 manifest them- 

 selves in a subdued form, in such phenomena 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 moment. 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 com- 

 paratively 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 sur- 

 rounding country. The district known as the Eifel, on the 

 west bank of the Rhine, between Bonn and Andernach, 

 offers equally striking examples of extinct volcanoes. 



Even in the British Isles, it is not difficult to trace the 

 remains of ancient volcanic outbursts, although these are not 

 so fresh and well-marked as those just mentioned. Sheets 

 of lava are found in the north-eastern part of Ireland, espe- 

 cially in the county of Antrim, where the remarkable scenery 

 of the Giant's Causeway is due \o the fact that some of the 

 old lava has split up into columns, not altogether unlike 



