82 Baron Cuvier's Lectures on the Natural Sciences. 



that it resembles the mullet, in the round form of the head, in 

 its colour, and the disposition of its scales. 



Theophrastus Avrote also a small treatise on animals that change 

 their colour. In this treatise, he speaks of the various colours 

 assumed by the cameleon, and the change of tint which takes 

 place in the hair of the reindeer, — a change which he considers 

 as dependent upon the will of the animal, but which, in reality, 

 is only an effect of the seasons. In another little work upon 

 animals of sudden appearance, he seems not much disposed to 

 admit spontaneous generation ; and if he does not altogether 

 reject it, at least he hmits it a good deal more than his master 

 did. 



The most important of the works of Theophrastus, next to 

 his two books upon botany, is his treatise on stones, a work 

 valuable on account of the number of mineral species that are 

 pointed out in it. Theophrastus wrote also a treatise on metals, 

 but this treatise is lost. He considers metals as deriving their 

 origin from water, and stones as produced by the earth. He 

 makes a division among stones, distinguishing them as fusible 

 and infusible ; and these last, again, as calcinable stones, and 

 stones which are unalterable by fire. He groups all the mineral 

 substances which have a common property, as amber and the 

 loadstone, both of which have a power of attraction. He shews 

 the uses of tlie touchstone, speaks of the different kinds of petri- 

 faction, and of petrifying waters. 



From these general considerations, he goes to particular de- 

 scriptions. He speaks of different marbles, of the Parian marble, 

 pentelic marble, alabaster, and a good many others that are 

 used by architects and sculptors. He treats of the stones 

 which are reduced for extracting metals, of pit-coal and its dif- 

 ferent species. He compares amber with a variety of this mine- 

 ral which is found in Liguria, and it is a very just comparison. 



He mentions also pumice-stones ; he knew their volcanic ori- 

 gin, and gives to one of the species the name of Lipari-stone. 

 He gives a description of the amianthus, which is indestructible 

 by fire ; and of another substance, like rotten wood, which, when 

 soaked in oil, burns with a flame. 



Next came the stones fit for engraving; the carnelian, the 

 jasper, &c. Mention is made of a sapphire, which has a blue 



