HOT SPRINGS IN THE AZORES. 87 



A stream of lava soon cools and hardens on the surface, 

 but the great mass within retains its heat for years. In 1759, 

 the Mexican volcano Jorullo poured forth a perfect sea of 

 lava which completely filled the beds of the two rivers 

 Cuitemba and San Pedro for some distance. Both streams 

 disappeared on one side of the vast expanse ot molten rock, 

 but made their way beneath it and reappeared on the 

 opposite side as permanent springs pouring forth large bodies 

 of very hot water, which retained their heat for many years 

 after the eruption. At the present day the water is but a 

 few degrees warmer than the air; but for a hundred years 

 or so large quantities of steam continued to issue from the 

 volcano. 



All the Azores are islands of volcanic .origin, and in one 

 of them, San Miguel, there is an immense crater, which in 

 former times was no doubt a. lake of boiling lava, but is now 

 a wonderfully green and fertile hollow, called, from its 

 shape, the Cauldron of the Seven Cities, and containing two 

 lakes and many villages, whose white houses, meadows 

 gardens, and corn fields, lie at a depth of 1,500 feet below 

 the lip of the crater. 



San Miguel is still shaken by earthquakes from time 

 to time, and although there are no more eruptions, the under- 

 ground fires still burn well enough to keep the water in a 

 number of springs always boiling. These springs all empty 

 themselves into one small stream, which retains its heat for 

 several miles and carries down into the sea a great variety of 

 dissolved minerals. Hot water and steam are more power- 

 ful solvents than cold water, and being usually charged with 

 large quantities of carbonic acid, act very powerfully upon 



