dependiiig on their Internal changes. ^5 



der AJcad. der Wissenschaften zu Munchen fur 18J8 und 

 1819) various kinds of steatite, quoted by authors, some in 

 the form of garnet, others in the form of trigonal-dodecahe- 

 drons of an unknown mineral, engaged in the serpentine from 

 Siberia, others in the form of felspar, &c. yield examples of 

 such bodies. They have not yet been examined with that de- 

 gree of attention which they deserve, not so much perhaps on 

 their own account, as rather for the inferences to which re- 

 searches of this kind might lead. But it must be allowed, that 

 many of them cannot be instituted in those fragments of the 

 entire series, which, for their more apparent distinctness, are 

 preserved in our mineralogical cabinets. Beside extensive se- 

 ries of the minerals in question, they require the joint efforts of 

 mineralogical inquiry, for ascertaining the species which have 

 been destroyed, and those which have been formed ; of che- 

 mical examination, for ascertaining the difference in the ingre- 

 dients of the two ; and of geological observation of the speci- 

 mens in their natural repositories, in order to establish the 

 causes by which the chemical affinities, balanced by the forma- 

 tion of the original compounds, have again entered into action. 



From the preceding enumeration, it is but too evident, that 

 our knowledge of the facts, as well as of their causes, up to this 

 moment is scanty and imperfect. A wide field of research is 

 still open, promising a fair return for the labour naturalists 

 may bestow upon its cultivation. I have endeavoured to collect 

 only some of the most remarkable and familiar instances of the 

 changes which may take place in the solid body of a crystal, 

 the ulterior study of which, while it illustrates the idea of spe- 

 cies, will throw some light also on the causes of such alterations 

 as do not appear conformable to the known laws of chemical 

 affinity, for which we cannot account at least in the present 

 state of our information. 



