498 ADDRESS OF T. STERRY HUNT. 
by Daubrée that the elements of the zeolites had been derived in 
part from the waters, and in part from the mortar and even the 
clay of the bricks, which had been attacked, and had entered into 
combination with the soluble matters of the water to form chaba- 
zite. I, however, at the same time pointed out another source of 
silicated minerals, upon which I had insisted since 1857, viz.: 
the reaction between silicious or argillaceous matters and earthy 
carbonates in the presence of alkaline solutions. Numerous ex- 
periments showed that when solutions of an alkaline carbonate 
were heated with a mixture of silica and carbonate of magnesia, 
the alkaline silicate formed acted upon the latter, yielding a sili- 
cate of magnesia, and regenerating the alkaline carbonate ; which, 
without entering into permanent combination, was the medium 
through which the union of the silica and the magnesia was ef 
fected. In this way I endeavored to explain the alteration, in the 
vicinity of a great intrusive mass of dolerite, of a gray Silurian 
limestone, which contained, besides a little carbonate of magne- 
sia and iron-oxyd, a portion of very silicious matter, consisting 
apparently of comminuted orthoclase and quartz. In place of 
this, there had been developed in the limestone, near its contact 
with the dolerite, an amorphous greenish basic silicate, which had 
PATIRA resulted from the union of the silica and alumina with 
on-oxyd, the magnesia and a portion of lime. By the crys- 
niidi of the products thus generated it was conceiv ed that 
minerals like hornblende, garnet and epidote might be developed 
in earthy sediments, and many cases of local alteration explained. 
Inasmuch as the reaction described required the interv ention of 
alkaline solutions, rocks from which these were excluded would 
escape change, although the other conditions might not be want- 
ing. The natural associations of minerals, moreover, led me to 
suggest Son alkaline solutions might favor the cry stallization of 
aluminous silicates, and thus convert mechanical sediments in 
gneisses sin mica-schists. The ingenious experiments of Dau- 
brée on the part which solutions of alkaline silicates, at elevated 
temperatures, may play in the formation of crystallized minerals, 
such as feldspar and pyroxene, were posterior to my early publi- 
cations on the subject, and fully justified the importance which, 
early in 1857, I attributed to the intervention of alkaline baie 
in the formation of crystalline silicated minerals. * 
e 
*Proc, Royal Soc., May 7, 1857. Amer. Jour, Sci., I, xxiii, 438, and xxv, 289 and 435. 
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