COLLECTION OF MINERALS. 281 



When Tournefort visited it, he imagined that 

 stones vegetated in the manner of plants. He 

 brought home the beautiful concretion placed 

 at the bottom of the fourth case. The calcareous 

 alabaster, of which vases and statues were for- 

 merly made, and of which we have here several 

 specimens, is the result of successive deposits of 

 carbonate of lime : the layers of which form un- 

 dulations more or less distinct, and shew, when 

 polished, zones of different colours. 



When water, having calcareous particles in 

 solution, remains in a cavity of small extent, these 

 particles incrust the sides of the cavity, and line 

 it with crystals : this is called a geode. We see 

 on the stage of the fourth case an example, the 

 interior of which is lined with crystals belonging 

 to the metastatic variety. 



The liquid sometimes deposits particles, which 

 are held suspended, on the surface of different 

 organic bodies, and clothes them with a stony 

 envelope ; under which are preserved the prin- 

 cipal features which characterize the body. It is 

 this variety, named incrusting concretion, which 

 covers the branches and nests, which are at the 

 bottom of the fifth case. Next to these is an in- 

 crustation of a milk-white colour, presenting the 

 likeness of Galileo, from the baths of San Phi- 

 lippo, in Tuscany. Immediately over the stage 



