are however abundant; the lime-feldspars, scapolite, epidote (saussurite), 
and white garnet, all form beds in crystalline rocks. Reactions in water 
at the earth’s surface, and at no very elevated temperature, may have 
given rise to double silicates of lime and alumina corresponding to neo- 
lite, and allied in composition to the zeolites, and these by subsequent 
metamorphism have been changed into anhydrous silicates. The pro- 
duction of harmotome, chabazite and apophyllite by the waters of a 
spring at Plombiéres, at temperatures not above 160° F. as observed by 
Daubrée, lends probability to such a view. a 
But while we admit the possible direct formation of double silicates in 
water at ordinary temperatures, there is not wanting evidence that the 
reaction which we long since pointed out, (Proc. Royal Society of Lon- 
[2 xxv, 287), between silicious and argi 
h 5°5, 
In the ordinary modes of decomposition of minerals containing alu- 
Mina, this base separates in the form of si 
and the aluminous minerals from the : 
Berthier and Deville, show that free alumina 1s much more common in 
