376 STRUCTURE, AND MODE OP ACTION 



hemisphere, from the Equator to the Poles. In a remote island, sur- 

 rounded by exotic vegetation, beneath a sky where his accustomed 

 stars no longer shine, the voyager often recognizes with joy the 

 argillaceous schists of his birth-place, and the rocks familiar to his 

 eye in his native land. 



This absence of any dependence of geological relations on the 

 present constitution of climates does not preclude or even diminish 

 the salutary influence of numerous observations made in distant re- 

 gions on the advance and progress of geological science, though it 

 imparts to this progress something of a peculiar direction. Every 

 expedition enriches natural history with new species or new genera 

 of plants and animals : there are thus presented to us sometimes 

 forms which connect themselves with previously long known types, 

 and thus permit us to trace and contemplate in its perfection the 

 really regular though apparently broken or interrupted network of 

 organic forms : at other times, shapes which appear isolated either 

 surviving remnants of extinct genera or orders, or otherwise mem- 

 bers of still undiscovered groups, stimulating afresh the spirit of 

 research and expectation. The examination of the solid crust of the 

 globe does not, indeed, unfold to us such diversity and variety; it 

 presents to us, on the contrary, an agreement in the constituent 

 particles, in the superposition of the different kinds of masses, and 

 in their regular recurrence, which excites the admiration of the geo- 

 logist. 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 por- 

 phyry, abrupt precipices; and vitreous feldspathic trachyte, high, 

 dome-like elevations. In the most distant zones, large crystals se- 

 parate themselves in a similar manner from the compact texture of 

 the primitive mass, as if by an internal development, form groups 

 in association, and appear 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 represented, 

 as it were, with more or less distinctness; yet, in order to become 

 completely acquainted with the important phenomena of the com- 



