1 92 WHAT IS LIFE ? 



the rocks of the Secondary formation. Many of the 

 leading types of life which existed in the Primary rocks 

 now disappear. The trilobites have become extinct. 

 The rocks belonging to the Secondary era have not 

 generally been subject to the same marked distortion as 

 the primary rocks. There is an evident diminution of 

 volcanic activity. The vegetable world undergoes a 

 remarkable transformation. Ancient types of plants 

 peculiar to the Carboniferous and Permian formations 

 disappear and are replaced by cone-bearing and more 

 advanced types of trees. This division of the geological 

 record has been styled as " the age of Cycads," a 

 vegetable form already referred to. The vanguard of 

 the rich plant life of to-day appears. Animal Hfe also 

 advances. 



The lowest strata are called by geologists the Triassic 

 rocks ; they overlie and were deposited after the Permian 

 rocks. These layers consist for the most part of bright 

 red sandstone and clays or marls, often ripple-marked r 

 sun-cracked, rain-pitted, and marked with animal foot- 

 prints. 



When these rocks were deposited, plant life consisted 

 mainly of ferns, cone-bearers and cycads. A few of 

 the Carboniferous ferns survived. The earliest true 

 horsetails now spring into existence. Calcareous sea- 

 weeds abounded in the open seas of the time. 



Foraminifera, sponges and corals are in abundance. 

 Star-fish and their allies are plentiful. Certain localities 

 are rich in fossil sea-urchins, which appeared only 

 sparsely in the Primary rocks. A creature like our 

 living shrimp sprang into existence. Shell-fish progress 

 in complexity of structure. Fish exhibit no advance 

 upon previous formations. 



