CHAPTER XVII 



THE EVOLUTION OF CONTINUITY (continued) 



While the geological record does not supply the key to 

 the evolution of living Continuity, yet it throws valuable 

 light on the subject. 



The part of the earth in which we are interested is the 

 " crust," and lies superficially to the crystalline or Archaean 

 rocks, regarding whose origin geologists are still uncertain, 

 and which contain no traces of past life in any form. The 

 crust of the globe is composed of more or less distinct rock 

 layers or strata which have been successively deposited 

 through inconceivable stretches of time, and which contain 

 evidences of past life in the shape of fossil forms or casts of 

 plants and animals. 



These strata from below upwards are divided into four 

 great sections, namely, the Palaeozoic or Primary, the 

 Mesozoic or Secondary, the Cainozoic or Tertiary, and the 

 Post-Tertiary or Quarternary ; the adjectives being also 

 used to denote the periods of geological time during which 

 the rock-systems were being deposited and the living types 

 represented in their fossils flourished. Each section is 

 further divided into systems of strata or formations. The 

 following table shows the sections and systems ; the numerous 

 strata not being included : — 



Sections. Systems. Nature op Rocks. 



Recent. Pleisto- 



Post-Tertiary { ^^^ qi^ } Sand, gravel, day 



| Oligocene j limestones 



V. Eocene ■* 



/Pliocene 

 Miocene \- Sands, gravels, clays, marls, 



Secondary or f Cretaceous Limestone, chalk, sands 



Mesozoic < Jurassic Limestone, sands, clays 



I Triassic Marls, sandstones, limestone 

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