100 THE WONDERS OF GEOLOGY. Lect. I. 



a lagoon in a state of ebullition, which discharges its 

 waters into the Rotu-Mahanu."* 



These modern siliceous formations are facts of great 

 interest and importance ; for they prove, in the clearest 

 manner, that the most insoluble and refractory substance 

 may be reduced to a liquid state, and again become con- 

 solidated, and assume numerous modifications, merely by 

 the agency of thermal waters ; hence the envelopment of 

 the delicate corals, shells, &c. which are so abundant in 

 chalk flints, is readily explained. 



50. Artificial solution of silex. — The natural 

 processes above described, have been successfully imitated 

 in a series of experiments, conducted with great sagacity 

 by Mr. Jeffery, with the view of determining whether 

 silex is soluble in heated water, without the presence of 

 alkalies, or other chemical agents. The following is a 

 concise account of these important experiments. 



A large boiler, used for vitrifying brown stone-ware, 

 was heated by four exterior furnaces, each six feet long 

 and five wide. Between each of these furnaces and the 

 kiln a deep pit was made, and filled to a height of three feet 

 with water, which was renewable from without. Some fels- 

 pathic and siliceous minerals were placed in the direction 

 of the current just within the kiln ; and upon some of the 

 arches a few earthenware vessels were placed, that any 

 action upon them might be observed. Below a full red 

 heat but little effect was perceived ; but at a temperature 

 above that of fused cast-iron, a rapid solution of mineral 

 matter took place ; this heat was continued for ten hours. 

 When the kiln was opened, more than a hundred-weight 

 of mineral matter had been dissolved and carried away in 

 the vapour. The wall was eaten away, and presented a 

 corroded and unglazed surface, like loaf-sugar partially 



* Dr. Dieffenbach's New Zealand. 



