70 Intelligence and Miscellaneous Articles. 



Silica 74-5 



Alumina and oxide of iron .... 17*9 



Water 7-5 



This composition is nearly identical with that of the deposits 

 found in Iceland. DiefFenbach and Hooker found in the interior of 

 New Zealand a large number of volcanic springs of a high tempera- 

 ture, which deposited stony substances resembling chalcedony. 

 These deposits, analysed by Thomson, gave — 



Silica 77-35 



Alumina 9*70 



Peroxide of iron 3*72 



Lime 1 "54 



Water 7-66 



The composition is therefore the same, although the substances 

 were derived from such different localities. The comparison of the 

 analysis of the mud with that of the rock, shows that the potash and 

 soda being very soluble, have been carried off by the water ; that the 

 protoxide of iron has been converted into peroxide and accumulated 

 with the alumina in the deposit, whilst the silica has diminished ; 

 results whieh confirm Ebelmen's experiments. 



A crust of from 1 to 2 millimetres in thickness, which had been 

 formed on a rock bathed by the waters of the cascade, and which 

 was detached with facility, was also examined. It is very white 

 in the interior, but red on the outside ; muriatic acid destroys 

 this colour ; it is very hard, and presents a radiate crystallization. 

 From its composition it belongs to the class of zeolithes ; it con- 

 sists of — 



3934-0 



giving the formula (CaO, SiO^ + Al^ O^, 3Si03) -f 6H0. 



In the clefts of the source of the cascade, and under the arch 

 through which it issues, abundant white or yellowish efflorescences 

 are to be seen. Some portions of these are formed of potash alum, 

 wliilst others consist essentially of sulphate of soda. These salts 

 are nearly always mixed, and it is sufficient to dissolve them to 

 separate them from the silica. The solution when evaporated and 

 exposed to the air deposits crystals of alum, and the efflorescent sul- 

 phate of soda is readily got rid of. 



These productions are due evidently to the action of the air upon 

 the sulj)huretted hydrogen which is disengaged from the waters. 

 The rock exjjosed to the vapour of the water is much disintegrated ; 

 it becomes porous, and causes the sulphur to j)ass to the state of' 

 sulphuric acid, which assists in its turn in the attack upon the rock 



