ON THE ORIGIN OF COMPOUNDS, he states (_De Ortu_, p. 80): "There now remain for our consideration the compound minerals (_mistae_), that is to say, minerals which contain either solidified juice (_succus concretus_) and 'stone,' or else metal or metals and 'stone,' or else metal-coloured 'earth,' of which two or more have so grown together by the action of cold that one body has been created. By this sign they are distinguished from mixed minerals (_composita_), for the latter have not one body. For example, pyrites, galena, and ruby silver are reckoned in the category of compound minerals, whereas we say that metallic 'earths' or stony 'earths' or 'earths' mingled with juices, are mixed minerals; or similarly, stones in which metal or solidified juices adhere, or which contain 'earth.' But of both these classes I will treat more fully in my book _De Natura Fossilium_. I will now discuss their origin in a few words. A compound mineral is produced when either a juice from which some metal is obtained, or a _humour_ and some other juice from which stone is obtained, are solidified by cold, or when two or more juices of different metals mixed with the juice from which stone is made, are condensed by the same cold, or when a metallic juice is mixed with 'earth' whose whole mass is stained with its colour, and in this way they form one body. To the first class belongs _galena_, composed of lead juice and of that material which forms the substance of opaque stone. Similarly, transparent ruby silver is made out of silver juice and the juice which forms the substance of transparent stone; when it is smelted into pure silver, since from it is separated the transparent juice, it is no longer transparent. Then too, there is pyrites, or _lapis fissilis_, from which sulphur is melted. To the second kind belongs that kind of pyrites which contains not only copper and stone, but sometimes copper, silver, and stone; sometimes copper, silver, gold, and stone; sometimes silver, lead, tin, copper and silver glance. That compound minerals consist of stone and metal is sufficiently proved by their hardness; that some are made of 'earth' and metal is proved from brass, which is composed of copper and calamine; and also proved from white brass, which is coloured by artificial white arsenic. Sometimes the heat bakes some of them to such an extent that they appear to have flowed out of blazing furnaces, which we may see in the case of _cadmia_ and pyrites. A metallic substance is produced out of 'earth' when a metallic juice impregnating the 'earth' solidifies with cold, the 'earth' not being changed. A stony substance is produced when viscous and non-viscous 'earth' are accumulated in one place and baked by heat; for then the viscous part turns into stone and the non-viscous is only dried up."