200 



merous collections, which are the principal ob- 

 jects of their researches. This is not the feeling 

 of those, who, without confounding descriptive 

 mineralogy* with geognosy, endeavour to raise 

 themselves to ideas generally interesting, and 

 seek, in the study of nature, for answers to the 

 following questions : 



Is the conical mountain of a volcano entirely 

 formed of liquified matter, heaped together by 

 successive eruptions ; or does it contain in it's 

 centre a nucleus of primitive rocks covered with 

 lavas, which are these same rocks altered by 

 fire ? What are the affinities, which unite the 

 productions of modern volcanoes with the ba- 

 salts, the phonolites, and those porphyries with 

 basis of feldspar, which are without quartz, and 

 which cover the Cordilleras of Peru and Mexico, 

 as well as the small groups of the Monts d'Or, 

 of Cantal, and of Mezen in France ? Has the cen- 

 tral nucleus of volcanoes been heated in it's pri- 

 mitive position, and raised up, in a softened state, 

 by the force of the elastic vapours, before these 

 fluids communicated, by means of a crater, with 

 the external air ? What is the substance, which, 

 for thousands of years, keeps up this combustion, 

 which is sometimes so slow, and at other times 

 so active ? Does this unknown cause act at an 

 immense depth ; or does this chemical action 

 take place in secondary rocks lying on granite? 



The farther we are from finding a solution of 



* Oryctognosy. 



