DOMAIN V. CALCAREOUS. 



" The lake of Solfatara seems to have greatly 

 assisted in the formation of this rock. Its water, 

 charged with much gaz, explains by that qua- 

 lity the great number of hollows which travertine 

 presents. It proves that when the rock harden- 

 ed, a gaz has at the same time escaped in several 

 places, which has prevented the approximation 

 of its parts which were still soft. As often as 

 the interior of a mass of rocks presents cavities, 

 without any indication of foreign substances, 

 which might have opposed the union of its parts, 

 I conceive their origin may be attributed to the 

 escape of gaz, at the moment when the sub- 

 stance was passing from a state of softness to 

 solidity, by cooling or drying. 



" From what I have just shown, it follows that 

 travertine, or rock of Tibur or of Tivoli*, is a 

 carbonate of lime, formed by the depositions of 

 the Anio and the Solfatara of Tivoli. The 

 Roman artists give the name of travertine only 

 to the stone taken from the quarry, situated at 

 the foot of the mountain of Tivoli. The litho- 

 logists, less slaves to locality, bestow it on all 

 calcareous rocks which possess the grain, tissue, 

 and formation analogous to that of the traver- 

 tine of Tivoli. If the ancient and modern 



* Tilurtinum of the ancients. 



