16 THE STORY OF Tin: EARTH. 



lion; sometimes in islands rising from the sea, 

 Sometimes in mountain chains formed of islands 



united together The linear arrangement is at- 

 tributed to the opening of fissures, which pen- 

 downward along lines, in which the rocks 



have been folded and fractured in the pr< 

 upheaval. When rain water, in a region so bent 

 and strained, is held back upon the land and 

 hindered from escaping by the pressure of the 

 round its shores, the \sater descends through the 

 minor joints and capillary interspaces between the 



• rock. Then it rises in temperature 



with the internal heat of the earth, to facil- 



itate the melting of rocks, with which it combii 

 Some of this water eventually ascends through 

 the planes of fracture and displacement forming 

 outlets for - ve energy, discharging steam, 



dust, and the r<>ck matter, both solid and molten, 

 which builds volcanic com-. 



st periods of geological time abound in 



evid< f volcanic activity. From the imper- 



fect nature of the records which remain upon the 



linear arrangement is not , evi- 



• ; but they may be inferred to mark line- 

 upheaval which brought islands into exist* 



United them into continental ma- land in 



:ve epochs igical time, but be- 



- the volcanos which arc marked by bed 



fl( ,\\ B, and the tie > which 



matter ascended, then 



i the world extinct \< with their 



L8 though the craters 



th ol the Pyrenees, in the basin of 

 the Bbro, there are fifi Olol in 



a, btlilt b of which 



