232 THE WORLD OF LIFE 



Concluding Remarks on Mesozoic Life-Development 



The remarkable series of facts wliicL have now been sum- 

 marised, and which have been largely due to researches in 

 Xorth America, South Africa, and Europe during the last 

 twenty or thirty years, are of such a nature that they seem 

 to call for some cosmical explanation similar to that suggested 

 to account for the vast development of cryptogamous vegetation 

 towards the close of the Palseozoic era. The facts are in many 

 respects strikingly parallel. We find in the Carboniferous 

 series of rocks a storing-up of vast masses of vegetable matter 

 in the form of coal, which is unique in the whole past history 

 of the earth, and this was at a time when the only land verte- 

 brates were archaic forms of amphibians. Almost immediately 

 after the deposit was completed true reptiles appeared all over 

 the earth, and rapidly develoj^ed into that " Age of Eeptiles " 

 which is perhaps the greatest marvel of geological history. 

 Birds and Mammalia also started into life, apparently branch- 

 ing off from some common stock with the reptiles. Then, 

 during that blank in the record separating the Secondary from 

 the Tertiary era, the whole of this vast teeming mass of rep- 

 tilian life totally disappeared, with the two exceptions of the 

 crocodiles and the tortoises, which have continued to maintain 

 themselves till our own day, w^hile true lizards and snakes, 

 which are not known in earlier times, became the predominant 

 forms of reptilian life. It was during the same blank period 

 of the geological record that mammals and birds sprang into 

 vigorous and diversified life, just as the reptiles had done 

 during the blank between the Primary and Secondary eras. 

 To complete the great series of life-changes (perhaps as a nec- 

 essary preparation for them), plants underwent a similar trans- 

 formation; the prominent Cryptogams, Conifers, and Cycads 

 of the Secondary era gave way towards its close to higher flow- 

 ering plants, which thenceforth took the first place, and now 

 form probably fully 99 per cent of the whole mass of vegeta- 



