248 COSMOS. 



inuuixe particles were either dissolved or held in suspension, 



constituting the greater part of the secondary (or flotz) and 

 tertiary groups. 



Transformed or metamorphic rocks,* in which the interna* 

 texture and the mode of stratification have been changed, 

 either by contact or proximity with a plutonic or volcanic 

 endogenous rock of eruption,! or what is more frequently the 



* [As the doctrine of mineral metamorphism is now exciting very 

 general attention, we subjoin a few explanatory observations by the 

 celebrated Swiss philosopher, Professor Studer, taken from the Edinb. 

 New Philos. Journ., Jan. 1848 : "In its widest sense, mineral meta- 

 morphism means every change of aggregation, structure, or chemi- 

 cal condition which rocks have undergone subsequently to their deposi- 

 tion and stratification, or the effects which have been produced by other 

 forces than gravity and cohesion. There fall under this definition the 

 discoloration of the surface of black limestone by the loss of carbon ; 

 the formation of brownish red crusts on rocks of limestone, sandstone, 

 many slatestones, serpentine, granite, &c. by the decomposition of iron 

 pyrites, or magnetic iron, finely disseminated in the mass of the rock ; 

 the conversion of anhydrite into gypsum, in consequence of the absorp- 

 tion of water ; the crumbling of many granites and porphyries into 

 gravel, occasioned by the decomposition of the mica and felspar. In 

 its more limited sense, the term metamorphic is confined to those 

 changes of the rock Avhich are produced, not by the effect of the 

 atmosphere or of water on the exposed surfaces, but which are produced, 

 directly or indirectly, by agencies seated in the interior of the earth. 

 In many cases the mode of change may be explained by our physical 

 or chemical theories, and may be viewed as the effect of temperature or 

 of electro-chemical actions. Adjoining rocks, or connecting communi- 

 cations with the interior of the earth, also distinctly point out the seat 

 from which the change proceeds. In many other cases the metamorphic 

 process itself remains a mystery, and from the nature of the products 

 alone do we conclude that such a metamorphic action has taken place.l 

 Tr. 



+ In a plan of the neighbourhood of Tezcuco, Totonilco, and Moran, 

 (Atlas geograpliique et physique, pi. vii.) which I originally (1803) 

 intended for a work which I never published, entitled Pasigrafia Geo- 

 gnostica destinada al vso de los Jovenes del Coleyio de Mineria de 

 Mexico, I named (in 1832) the plutonic and volcanic eruptive rocks 

 endogenous (generated in the interior), and the sedimentary and flotz 

 rocks exogenous (or generated externally on the surface of the earth). 

 Pasigraphically, the former were designated by an arrow directed up- 

 rards f , and the latter by the same symbol directed downwards I . 

 These signs have at least some advantage over the ascending lines, whicfc 

 in the older systems represent arbitrarily and ungracefully the horizon- 

 tally ranged sedimentary strata, and their penetration through masses 

 ( basalt, porphyry, and syenite. The names proposed in the pasigra 



