154 INORGANIC EVOLUTION. [CHAP. 



velopment ; but we still have our seaweed ; so that with all the change 

 in some directions, some forms like the earlier survive,. 



After this explanation, relating to work in an apparently different 

 direction, there should be no difficulty, in understanding the meaning I 

 attach to the word " evolution " so far as the history of plant change 

 is concerned, in relation to the chemical elements ; but we are not 

 limited to plant life. The same conceptions apply to animal life, and 

 it is important for my subject that I should refer to that also. What 

 do we find there ? We are brought face to face with the same pro- 

 gression from simple to complex forms. This is best studied by a 

 reference to the geological record. 



Stratigraphical geology is neither more nor less than the anatomy 

 of the earth,* arid . the history of the succession of the formations is 

 the history of a succession of such anatomies ; or corresponds with 

 development as distinct from generation. In Stratigraphical geology, 

 as can be gathered from any book on the subject, we find the names 

 of certain beds which contain certain different forms of animal and 

 vegetable life. We begin with the Laurentian and Algonkian and 

 then pass to the Cambrian, then to the Ordovician, the Silurian and 

 Devonian, and so on through a long list of beds and geological 

 strata until we come eventually to the Eecent, that is to say, 

 the condition of things which is going on nowadays on the surface 

 of the earth. And if we prefer to map those many different 

 beds into more generic groupings, we begin with the Primary or 

 Palaeozoic, we pass on to the Secondary or Mesozoic, and then we 

 finally reach the Tertiary or Cainozoic. The deposition of these beds 

 and of the animal life which has been going on continuously on the 

 surface while those beds have been deposited, gives us the various 

 changes and developments which have taken place with regard to 

 animal forms. 



It is worth while to go a little more into details and to indicate 

 the changes in these forms which have taken place, in the most general 

 way. Beginning with the Lower Cambrian, we find that the animal 

 forms were represented by Irrvertebrata such as Sponges, Corals, 

 Echinoderms, Brachiopods, Mollusca, Crustacea with many early Trilo- 

 bites; not to mention true Fucoids and other lowly plant-remains. 

 When we come to the Silurian, we find a large accession of the above 

 forms, especially of Corals, Crinoids, and Giant Crustaceans (such as 

 Pteryyotus) and armoured animals (Ostracodermi) without a lower jaw, 

 or paired fins ; the beginnings of Vertebrate life, ,not yet fully evolved, 

 and one lowly organised group of armoured fishes named Cyatluispis 

 (without bone-cells in their shelly-shield). Here, too, we meet with 

 * Huxley, Q.J.G.S., vol. xxv, p. 43. 



