436 Correspondence of T. S. Hunt. 
glasses, containing lime and iron, are heated in the same way to 400° C, 
in the presence of a small amount of water. The alkaline silicate which 
separates from the decomposition of the glass is resolved into quartz, 
which forms regular crystals, and a soluble silicate having the formula 
SiO, KO. 
These results of Mr. Daubrée serve in the most remarkable manner to 
confirm my theory of the normal metamorphism of sedimentary rocks at 
temperatures below ignition, by the intervention of solutions of alkaline 
silicates, which convert mixtures of quartz and earthy carbonates into the 
corresponding silicates, and clays into feldspars and mica, the intervention 
alumina sometimes generating chlorite, epidote and garnet. 
Danbrée* remarks that glass when thus heated in presence of water 
swells up, indicating a softening and a plasticity of the mass, and he 
observes that his experiments enable us to understand the part which 
water may have played in the formation of the igneous rocks. His ob 
tio oul 
Sir John F. W. Herschel many years since put forward a theory of 
_ Voleanos, in which he suggested that all volcanic and plutonic rocks were 
o other than sedimentary deposits, melted down with their included 
origin, and the intrusive form so often assumed by granites, itp 
accidental, sn 
In my report for 1856, p. 485, I have. insisted that the soperylien 
oxyd of iron from certain strata, and its accumulation-in. others, 18 to > 
ascribed to the reducing and solvent action of organic matters. This 1s 
exemplified in the fire-clays and iron-stones of the coal formation, & he 
as in the series of the Hudson river group described in my Report, n *¥) 
ire-clays and greensands of the cretaceous formation of New ae “ 
many other instances. It is by the alteration of such psig ae — 
rmed, @ 
Laurentian or so-called Azoic period. also 
The waters which dissolve out the oxyd of iron from ne th 
