224 REACTION OF THE INTERIOR OF THE EARTH 



which, showed itself in a wide plain in a district remote 

 from any active or extinct volcanoes ; in the island of 

 Euboea, the modern Negropont. " The violent shocks 

 of earthquake, which partially shook the island, did not 

 cease until an abyss, opened in the plain of Lelantus, 

 poured forth a stream of glowing mud (lava)." ( 30G ) 



If, as I have long been disposed to conjecture, we 

 may ascribe to a first fissuring of the deeply disturbed 

 earth-crust the oldest formations of eruptive rocks (often 

 perfectly similar in mineral composition to recent lavas), 

 then these fissures, as well as the craters of elevation of 

 later origin and already less simple, must be looked 

 upon only as volcanic openings through which erupted 

 masses have flowed, and not as volcanoes proper. The 

 principal character of these latter consists in a per- 

 manent, or at least from time to time renewed, con- 

 nection between the deep-seated focus or source of 

 igneous action, and the atmosphere. The volcano re- 

 quires for this purpose a particular kind of framework ; 

 for, as Seneca says very appositely in a letter to 

 Lucilius, f( ignis in ipso monte non alimentum habet, 

 sed viam." ( 307 ) In regard to volcanoes, therefore, the 

 form-giving, or shaping, activity is exerted by the 

 upheaval of the ground; not (as was formerly and 

 almost exclusively believed) in building up by suc- 

 cessive accumulation of scoriae and strata of lava 

 deposited one above another. The resistance which 

 the fiery-fluid masses, pressed in too great abundance 

 against the surface, find in what is to be the channel of 

 eruption, occasions the augmentation of the upheaving 

 force. There arises a "bubble-shaped pushing-up of 

 the ground," as is indicated by the regular outward 



