24 GENERAL PRINCIPLES. 



gneiss, greenstone, lava, &c., and the result was, that all of them were acted upon by the carbonated water, 

 and in a slight degree by pure water. Quartz was not among them. This in a pure state is absolutely 

 insoluble by water, or by any acid, save the fluoric. There is a form of silica which is soluble, and if it be 

 converted into silicates, as in most of the minerals used by the Professors Rogers, it is soluble, and is found in 

 most mineral waters. The decomposition of these silicates is accomplished in a variety of ways, and usually 

 leaves an excess of silica in a free state, which forms quartz. 



How deep water penetrates into the crust of the earth we know not. But we know 

 that it possesses an astonishing power of working its way into fissures and pores. 

 Especially when converted into steam and kept in by strong pressure, we can hardly set 

 bounds to its interpenetration. We know that rocks deposited in water are several miles 

 thick, and in some of them water is chemically combined. 



We might suppose that the increasing heat, as we descend into the earth, would expel all 

 the water, or at least drive it near the surface. But the phenomena of volcanoes lead to a 

 different conclusion. The immense quantities of steam that are poured forth from the 

 craters demonstrate the presence of water at a great depth, as do the eruptions of mud, 

 called moya, in South America and in the Caucasus, and which in one volcano in Java 

 became a river of mud and diluted sulphuric acid. But the most remarkable fact of all 

 is, that ejected molten lava probably owes its liquidity to water. When a stream of it is 

 poured forth, steam escapes from the surface, and a crust is formed in consequence, which 

 prevents the escape of the condensed steam within, except when cracks are formed ; and 

 hence the fluid state is preserved within for a long time ; nor till that has escaped will it 

 be consolidated ; so that in the opinion of some of the ablest writers on volcanoes, such as 

 Scrope, liquid lava is an aqueo-igneous fusion. The heat is found to be not high enough 

 to produce liquidity without water. 



Suppose now the water in the stratified rocks to be highly heated, and yet essentially 

 imprisoned by impervious strata at the surface ; it is easy to conceive that it might 

 reduce the rock to a fluid or semifluid condition, without destroying the planes of stratifi- 

 cation, or producing a complete fusion like that of lava. In that state such chemical 

 changes might occur as would give a crystalline structure, form new simple minerals, and 

 produce planes of cleavage, foliation, and joints. 



But though hot water and steam would produce powerful metamorphic effects, they 

 would be very much increased if we suppose that water to contain in solution chemical 

 agents of great power ; for instance, carbonic, sulphuric and muriatic acids, sulphureted 

 hydrogen, and alkaline carbonates. There is no rock, except perhaps pure quartz, that 

 could withstand their combined action. They would all be softened and made so plastic 

 that in the course of centuries all the changes exhibited by metamorphic rocks might be 

 brought about. 



We have a very striking example of such agencies, in the account given us by Forest Shepherd, Esq., of 

 "the Pluton Geysers of California." These are hot springs, which throw out intermittingly and spasmod- 

 ically, powerful jets of steam and scalding water; their temperature varying from 93 to 1G9 Fahr. 

 Sulphuric acid and sulphureted hydrogen at least, according to Mr. Shepherd's account, are present, and 

 probably other energetic ingredients. Says Mr. Shepherd, "You find yourself standing not in a solfatara, 

 but in one of the salses described by the illustrious Humboldt. The rocks around you are rapidly dissolving 

 under the powerful metamorphic action going on. Porphyry and jasper are transformed into a kind of 



