SILICIOUS PETRIFACTIONS. 231 



It was discovered by Gay Lussac, that the 

 solubility of sulphate of soda in water, is aug- 



ling white marble. This is an exceedingly interesting and im- 

 portant fact to the geologist. The author was once greatly 

 embarrassed on finding beautiful strata of perfectly white siiicious 

 rocks, which had been obviously deposited from water, inclosed 

 between masses of basalt, greenstone, and other volcanic rocks in 

 the mountains of North Carolina, more than 4000 feet above the 

 ocean level. As all the other portions of those mountains con- 

 sisted of granite, gneiss, porphyry, and other igneous rocks which 

 had been elevated by subterranean heat, the existence of the 

 white sedimentary rocks remained a mystery, until the agency of 

 hot springs was investigated. 



The geysers rise up through volcanic rocks, in an island where 

 the eruptions of lava are so enormous, as to fill up gorges many 

 hundred feet deep, and two hundred feet wide. When not confined 

 in narrow valleys, they expand into broad lakes of melted rocks 

 that vary in thickness. Were such eruptions to cover the white 

 siiicious strata deposited by the geysers, (as they undoubtedly 

 have done, and will do again,) they would be inclosed between 

 igneous rocks, like the snow-white flinty strata in the mountains 

 of North Carolina. All animal and vegetable petrifactions com- 

 posed of silex, have been doubtless formed in waters holding this 

 mineral in solution, from the most minute animalcules and deli- 

 cate moss agates, to the largest fragments of silicified wood. Mr. 

 Barrow states, that on the margins of the numerous little streams 

 in the neighbourhood of the great Geyser, every description of 

 wood, bones, the horns of animals, and even paper, worsted 

 stockings, handkerchiefs, &c. were found in a silicified state. 



The steam emitted from volcanos is charged with a great variety 

 of rocks, salts, and metals, in a state of solution, which are de- 

 posited in the crystalline form as the solutions cool down. When 

 melted silex cools under the pressure of a mass of lava, making 

 rock crystal, a portion of steam is sometimes inclosed within its 

 centre, and condensed into water, where it remains for unlimited 

 periods of time. All geodes are probably formed by the cooling 

 down of lava, that contained steam or other gaseous fluids within 

 their interior, that escape by percolation, if the rocks be porous, 

 leaving their centres hollow. 



