28 Sketch of a Classification of the European Rods. 



ces far distant from each other. Let us for the moment suppose this 

 assertion to be correct. To obtain this uniform distribution of ani- 

 mal and vegetable hfe, it seems necessary, judging from the pha3- 

 nomena we now w^itness, that there should also have been an uni- 

 form temperature over the surface of our planet. To obtain this, 

 solar influence, as it now exists, would be inadequate; w^e must 

 therefore have recourse to internal heat to produce the effect requh'- 

 ed. In the present varied temperature of the earth's surface, if we 

 imagine a rock to be formed which should envelop every animal and 

 plant now existing, the fossil contents of one district w^ould differ 

 from the fossil contents of another; if we except man, whose bones 

 would more or less become the characteristic fossils of those por- 



r 



tions of the rock which might overlie the present dry land. The 

 rock supposed to be now formed would present a striking contrast 

 with the old fossiliferous, and we should have two very distinct ac- 

 cumulations of organic remains. The question arising on such phse- 

 nomena would be, Has so great a change of organic character been 

 effected gradually or suddenly? To suppose it sudden, will not 

 agree witli the phsenomena presented to us, even by the now known 

 European rocks ; and if it be considered gradual, we cannot expect 

 that rocks should every wdiere contain the same organic remains, 

 even in those that have commonly been called secondary : conse- 

 quently the organic remains considered characterisdc of any particu- 

 lar formation in one part of the world, may not be found at all in an 

 equivalent formation in another. 



Upon the theory that die world cooled in such a manner that so- 

 lar heat, as now existing, gradually acquired its influence, the warm 

 climate vegetation would gradually be restrained within narrower 

 limits, until it became circumscribed as it now is; consequently all 

 rocks formed wdthin the tropics w^ould probably contain w^arm cli- 

 mate plants, w^hile these would gradually cease on the N. and S. ; so 

 that it would be by no means safe to deduce the kind of Flora that 

 should be found in any given rock in the tropics from the fossil 

 plants discovered in an equivalent rock in Europe. If vegetable life 

 might under such circumstances so vary, there seems no good rea- 

 son why animal life might not equally differ. To what extent the 

 mass of organic fossils found in any particular European formation or 

 group of formations may exist in equivalent rocks (of Africa or Ame- 

 rica for instance), remains to be seen. In die present state of our 

 knowledge, it Is only safe to state that certain remains have been dis- 

 covered in a given rock, not that they are absent from It. 



m- 



