272 COSMOS. 



under definite relations; thus, for instance, although quarts; 

 (silica), feldspar, and mica, are the principal constituents 

 of granite, these minerals also occur, either individually 

 or collectively, in many other formations. By way of illus- 

 trating how the quantitative relations of one feldspathic 

 rock differ from another, richer in mica than the former, I 

 would mention that, according to Mitscherlich, three times 

 more alumina and one-third more silica than that pos- 

 sessed by feldspar, give the constituents that enter into the 

 composition of mica. Potash is contained in both, a 

 substance whose existence, in many kinds of rocks, is pro- 

 bably antecedent to the dawn of vegetation on the earth's 

 surface. 



The order of succession, and the relative age of the different 

 formations, may be recognized by the superposition of the 

 sedimentary, metamorphic, and conglomerate strata; by the 

 nature of the formations traversed by the erupted masses, and 

 with the greatest certainty by the presence of organic re- 

 mains and the differences of their structure. The application of 

 botanical and zoological evidence to determine the relative age 

 of rocks this chronometry of the earth's surface which was 

 already present to the lofty mind of Hooke indicates one of 

 the most glorious epochs of modern geognosy, which has 

 finally, on the Continent at least, been emancipated from the 

 sway of Semitic doctrines. Palaeontological investigations 

 have imparted a vivifying breath of grace and diversity to the 

 science of the solid structure of the earth. 



The fossiliferous strata contain, entombed within them, the 

 floras and faunas of bygone ages. We ascend the stream of 

 time, as in our study of the relations of super-position we 

 descend deeper and deeper through the different strata, in 

 which lies revealed before us a past world of animal and vege- 

 table life. Far-extending disturbances, the elevation of great 

 mountain chains, whose relative ages we are able to define, 

 attest the destruction of ancient, and the manifestation of 

 recent organisms. A few of these older structures have 

 remained in the midst of more recent species. Owing to the 

 limited nature of our knowledge of existence, and from the 

 figurative terms by which we seek to hide our ignorance, we 

 apply the appellation recent structure to the historical pheno- 

 mena of transition manifested in the organisms, as well as in 



