354 VIEWS OP NATURE. 



forms of vegetation, and beneath a sky beaming with other 

 stars than those to which his eye had oeen accustomed, the 

 mariner often recognises, with joyful surprise, argillaceous 

 schists and rocks familiar to him in his native land. 



This independence of geological relations on the actual 

 condition of climates does not diminish the beneficial influ- 

 ence exercised on the progress of mineralogy and physical 

 geognosy by the numerous observations instituted in distant 

 regions of the earth, but simply gives a particular direction 

 to them. Every expedition enriches natural history with new 

 genera of plants and animals. At one time we acquire a 

 knowledge of new organic forms which are allied to types 

 long familiar to us, and which not unfrequently, by furnishing 

 links till then deficient, enable us to establish, in all its ori- 

 ginal perfection, an uninterrupted chain of natural structures. 

 At another time we become acquainted with isolated struc- 

 tures, which appear either as the remains of extinct genera, 

 or members of unknown groups, the discovery of which sti- 

 mulates further research. It is not, however, from the inves- 

 tigation of the earth's crust that we acquire these manifold 

 additions to our knowledge, for here we meet rather with an 

 uniformity in the constituent parts, in the super-position of 

 dissimilar masses, and in their regular recurrence, which 

 cannot fail to excite the surprise and admiration of the 

 geologist. In the chain of the Andes, as in the mountains 

 of Central Europe, one formation appears, as it were, to call 

 forth another. Masses identical in character assume the same 

 forms; basalt and dolerite compose twin mountains; dolo- 

 mite, sandstone, and porphyry form abrupt rocky walls ; while 

 vitreous trachyte, containing a large proportion of feldspar, 

 rises in bell-shaped and high- vaulted domes. In the most 

 remote regions large crystals are separated in a similar manner 

 from the compact texture of the fundamental mass, and, 

 blending and grouping together into subordinate strata, fre- 

 quently announce the commencement of new and independent 



