or VOLCANOS. 215 



riety ; it presents to us, on the contrary, an agreement in 

 e constituent particles, in the superposition of the 

 'erent kinds of masses, and in their regular recurrence, 

 hich excites the admiration of the geologist. In the chain 

 of the Andes, as in the mountains of middle Europe, one 

 formation appears, as it were, to summon to itself another. 

 Rocks of the same name exhibit the same outlines ; basalt 

 and dolerite form twin mountains ; dolomite, sandstone, and 

 porphyry, abrupt precipices ; and vitreous feldspathic tra- 

 chyte, high dome-like elevations. In the most distant zones 

 large crystals separate themselves in a similar manner from 

 the compact texture of the primitive mass, as if by an 

 internal development, form groups in association, and ap- 

 pear associated in layers, often announcing the vicinity of 

 new independent formations. Thus in any single system of 

 mountains of considerable extent we see the whole inorganic 

 substances of which the crust of the earth is composed re- 

 presented, as it were, with more or less distinctness ; yet, in 

 order to become completely acquainted with the important 

 phenomena of the composition, the relative age, and mode 

 of origin of rocks, we must compare together observations 

 from the most varied and remote regions. Problems which 

 long perplexed the geologist in his native land in these nor- 

 thern countries, find their solution near the equator. If, as 

 has been already remarked, new zones do not necessarily pre- 

 sent to us new kinds of rock (i. e. unknown groupings or 

 associations of simple substances), they, on the other hand, 

 teach us to discern the great and every where equally pre- 

 vailing laws, according to which the strata of the crust of 



