THE EARTH'S INTERNAL HEAT. 1 7 



lava has flowed in streams still to be traced, yet 

 so long since that the existing rivers have cut 

 passages for themselves through the lava. 



The Auvergne is a granite platform in which 

 some ancient rocks of the carboniferous period 

 occur. This district appears to have been an is- 

 land traversed by a line of fracture from N.W. to 

 S.E., which corresponds to the uplifting of the 

 crystalline rocks. A second fracture runs from 

 N. to S. In this region are the ruins of the four 

 grand volcanos known as Mont Pore, Cantal, 

 Canton d'AllbraC, and Mc/cn. The lava flowed 

 from Mont Dore for 20 miles. The minor cones, 

 of which there are hundreds, range through the 

 country in a broad band, from N. to S. Many 

 have the craters burst down by the lava which 

 ascended in them, and overflowed into the neigh- 

 bouring vail' 



. it i fully preserved volcanic cones are found 

 to the north of the Moselle river in the district 

 known as the lower Kifel. It may have been in 

 this country that the eruption took place which is 

 mentioned by Tacitus as having affected the 

 country near Cologne, in the reign of the Roman 

 Emperor Nero. For a long way up the Rhine 

 the rocks are volcanic; and evidences of extinct 

 volcanos are found west of the Rhine, in many 

 parts of central Germany; and a series ranges 

 through Hungary S.W. of the Carpathians into 

 Servia. 



The latest volcanic outbursts in the British 

 Isles were at the beginning of the Tertiary period 

 in Skye, Rum, Mull and the adjacent mainland of 

 Scotland, and in the north of Ireland, where 

 streams of mud due to volcanic dust, washed 

 down by rains, covered up the vegetation of the 

 2 



