PART II. 



ORGANIC REMAINS. 



CHAPTER XLIII. 



Introductory View of the Distribution of Organic Remains in the Older Formations. 



GEOLOGY reveals to us the extraordinary fact, and without its aid the fact never 

 could have been known, that as the globe passed from one condition to another, whole 

 races of animals perished, and were succeeded by others with organizations adapted 

 to the altered state of our planet. 



On this phenomenon is based the fundamental principle of the identification of strata 

 by their imbedded remains ; the passage from one deposit to another being marked by 

 a change in the animals which lived and died during the accumulation of each. Thus, 

 although the fossils of any one great series of beds possess a common character, yet 

 those which are found in the lowest and highest strata of a great formation are for the 

 most part dissimilar in species, and often in genera. 



This principle, so little adverted to in the early days of the science, and yet so vitally 

 essential to its advance, has hitherto been chiefly tested by the examination of the tertiary 

 and secondary deposits, and its complete development required, that succeeding ob- 

 servers should laboriously work out its application to the numerous older strata which 

 are contained in the crust of the globe. In the progress of inquiry, this method of 

 proof having been sometimes too minutely exercised, and at others too vaguely, has 

 undeservedly incurred discredit. Some persons, for example, have endeavoured to show, 

 that because within a limited area every succeeding stratum was charged with peculiar 

 species, so we ought to find the same distinctions universally ; while others, merely com- 

 paring lists of species in the works of authors of different countries, or erroneously 

 identifying figures and descriptions of fossils, have inferred, that many species have a 

 much wider range in the geological scale than experience confirms. 



