630 GEOLOGY. 



thermometric conductivity, the flow of heat from the deep interior to 

 the middle zone would be greater than the loss of this zone to the super- 

 ficial zone. This middle zone should, under this view, experience a 

 rising temperature. By hypothesis, this zone is composed of various 

 kinds of matter mixed as they happened to fall in. Hence as the tem- 

 perature rises, the fusion-points of some of these constituents will be 

 reached before those of others. More strictly, the temperatures at 

 which some of these constituents will mutually dissolve one another 

 will be reached, while other constituents remain undissolved, and thus 

 a partial and distributed liquefaction will arise. The gases and vola- 

 tile constituents in the mixed material would naturally enter largely 

 into the liquefied portion. It is assumed that with a continued rise of 

 temperature, the partial liquefactions would increase until the liquefied 

 parts found means of uniting, and the lighter portions, embracing the 

 gaseous contingent, were able to work their way toward the surface. 

 As they rose by fusing or fluxing their Avay, the pressure upon them 

 became less and. less, and hence the temperature necessary for lique- 

 faction gradually fell, leaving them a constantly renewed margin of 

 temperature available for melting their way through the upper horizons. 

 Thus it is conceived that these fusible and fluxing selections from the 

 middle zone might thread their ways up to the zone of fracture and 

 thence, taking advantage of fissures and fractures, reach the surface. 

 It is conceived that such liquefaction and extrusion would carry out 

 from the middle zone the excess of temperature received from the deeper 

 interior, and thus regulate its temperature and forestall general lique- 

 faction, the zone as a whole remaining always sohd. The independence 

 of volcanoes is assigned to the independence of the liquid threads that 

 Avorked their way to the surface. Nothing like a reservoir or molten 

 lake enters into the conception. The prolonged action of volcanoes 

 is attributed to the slow feeding of the liquid threads from the locally 

 fused middle zone. The frequent pauses in action are assigned to tem- 

 porary deficiencies of supply; the renewals to the gathering of new 

 supplies after a sufficient period of accumulation. The distribution 

 of volcanoes in essentially all latitudes and longitudes is assigned to 

 the general nature of the cause. The special surface distributions are 

 assumed to be influenced, though not altogether controlled, by the favor- 

 able or unfavorable conditions for escape presented by the crustal seg- 

 ments of the earth. The persistence of volcanic action in time is attri- 



