MODE IX. AMYGDAL1TE. C; [ 



and clay, which is also the chief repository of 

 prehnite. The other formation belongs to his 

 Floetz, horizontal, or stratiform rocks ; and he 

 also describes the base of this as being wacken, 

 or rather decomposed grunstein, which, accord- 

 ing to his theory, generally lies under basaltin 

 and above clay. But Mr. Jameson, to whom 

 we are greatly indebted for an exposition of the 

 Wernerian system, omits amygdalite in his de- 

 scription of wacken ; and Brochant regards the 

 base of amygdalite as a decomposed siderite or 

 grunstein, and it certainly belongs to this do- 

 main. It is believed that olivine, though fre- 

 quent in basaltin, has never been observed in 

 amygdalite, in which the silicious parts assume 

 a different form. 



Some French mineralogists have supposed Origin, 

 amygdalite to be of volcanic origin ; but Patritt, 

 though an ardent volcanist, has rejected this 

 idea, and arranges it after porphyry, as he ob- 

 serves that the base is sometimes siderite, some- 

 times trap. The cavities are also larger than 

 any found in lava; and though agates be so 

 named from the river Achates in Sicily (in the 

 south of that country, and at a great distance 

 from Etna), it appears not that agates have ever 

 been observed in any volcanic region. 



Amygdalite, like basalt, often contains no* 



