AND THEIR DESCENDANTS 



thing of value about the world's climate in the earliest 

 eras. 



When we come to the Cambrian, however, we are on 

 firmer ground. In the Cambrian rocks there is, for the 

 first time, a fair preservation in fossil form of the life 

 of the period. Even here the record is far from com- 

 plete, but it is an immeasurable advance on the records 

 of previous periods. The most striking thing about this 

 comparatively plentiful appearance of life is that while 

 the animal kingdom is fairly well represented the plant 

 remains are hardly to be recognised at all. Yet there 

 must have been plants if only to feed the animals, and 

 we have very good reasons for believing that the surface 

 of the land was clothed with some form of vegetation. 

 Not a few of the Cambrian animals were fixed to the 

 bottom of the sea, and therefore there must have been 

 enough matter of some organic kind floating in the 

 water to bring them their daily food. Possibly many 

 of the plants were of the minute kind which forms scum 

 on rivers and ponds, and so would not readily leave fossil 

 impressions. Turning to the record of animal life, it 

 appears that nearly every division of the animal kingdom, 

 except such as had backbones, had some kind of a repre- 

 sentative in Cambrian times. Crustaceans, molluscs, worms, 

 corals, jelly fish, sponges, quite a large variety of sea- 

 animals, suddenly make their appearance, and although 

 no traces of land animals have yet been found, we have 

 reason to believe that some land animals may have 

 existed. Our reason is that in the next era but one 

 (Silurian) scorpions and insects appear, and these are 



203 



