Page:The fairy tales of science.djvu/305

Rh birds' nests, medallions, moss, and even old wigs, by the action of the petrifying springs of Derbyshire, is known to every one who has visited that romantic and interesting county.

In Italy large masses of solid and beautiful travertine are deposited by some of the springs; and in the famous Lake of the Solfatara, the formation of this stone is so rapid, that insects as well as the plants and shell-fish are frequently incrusted and destroyed. A considerable number of edifices in Italy, both ancient and modern, are constructed of stone thus formed. The Cyclopean walls and temples of Paestum, and the Colosseum at Rome, are built of huge blocks of travertine, which must have been deposited particle by particle, in lakes similar to that of the Solfatara.

But the most remarkable instance of the rapid formation of marble occurs in Persia. The beautiful transparent stone called Tabreez marble is formed by deposition from the water of a celebrated spring which rises near Maragha. Here the process of petrifaction may be traced from its first beginning to its termination. In one part the water is perfectly clear; in another dark, muddy, and stagnant; in a third it is quite black, and very thick; while in the last stage it is as white as snow. The petrified ponds look like frozen water; a stone thrown upon them breaks the crust, and a black fluid