INTKODTTCTION. O 



destructive agents, and as constantly forming before our eyes 

 for the most part periodic rocks (rocks of eruption); we 

 have likewise shown in contrast with this formation how sedi- 

 mentary rocks are in the course of precipitation from fluids, 

 which hold their minutest particles in solution or suspension. 

 Such a comparison of matter still in the act of development 

 and solidification with that already consolidated in the form 

 of strata of the earth's crust, leads us to the distinction of 

 geognostic epochs, and to a more certain determination of the 

 chronological succession of those formations in which lie 

 entombed extinct genera of animals and plants the fauna 

 and flora of a former world, whose ages are revealed by the 

 order in which they occur. The origin, transformation, 

 and upheaval of terrestrial strata, exert, at certain epochs, an 

 alternating action on all the special characteristics of the 

 physical configuration of the earth's surface ; influencing 

 the distribution of fluids and solids, and the extension and 

 articulation of continental masses in a horizontal and vertical 

 direction. On these relations depend the thermal conditions 

 of oceanic currents, the meteorological processes in the aerial 

 investment of our planet, and the typical and geographical dis- 

 tribution of organic forms. Such a reference to the arrangement 

 of telluric phenomena presented in the picture of nature, 

 will, I think, suffice to show that the juxtaposition of great, 

 and apparently complicated, results of observation, facilitates 

 our insight into their causal connection. Our impressions of 

 nature will, however, be essentially weakened, if the picture 

 fail in warmth of colour by the too great accumulation of 

 minor details. 



In a carefully-sketched representation of the phenomena 

 of the material world, completeness in the enumeration of 

 individual features has not been deemed essential, neither 

 does it seem desirable in the delineation of the reflex 

 of external nature on the inner man. Here it was 



