EXTINCTION OF TYPES. ti 



rank, but it must be remembered that though the oldest 

 (Archaean or Laurentian) rocks bear evidence {e.g., in the 

 occurrence of marble and carbonaceous material) that forms 

 of life existed when these rocks were formed, we have 

 practically no means of knowing what the forms of life were. 

 The Archasan rocks have been subjected to alterations far 

 too serious to admit of the preservation of fossils. If this 

 fact be fairly considered, there is no difficulty in under- 

 standing the presence of fairly complex animals in the rocks 

 of the next great age, which is usually called Cambrian. 



Extinction of Animals. — Some animals, such as some of 

 the lamp-shells or Brachiopods, have persisted from almost 

 the oldest ages till now, and most fossilised animals have 

 modern representatives which we believe to be their direct 

 descendants. That a species should become extinct need 

 not in the least surprise us, if we believe in the "trans- 

 formation " of one species into another. The extinction is 

 more apparent than real, the species lives on in its modified 

 descendants, " different species " though they be. 



But, on the other hand, there are not a few fossil animals 

 which have become wholly extinct, which are, in other words, 

 without any direct descendants now alive. Such are the 

 ancient Trilobites (probably remotely connected with our 

 king-crab), their allies the Eurypterids, two classes of 

 Echinoderms (Cystoids and Blastoids), many giant Reptiles, 

 and some Mammals. 



It is almost certain that there has been no sudden 

 extinction of any animal type. There is no evidence of 

 universal cataclysm, though local fioods, earthquakes, and 

 volcanic eruptions occurred in the past, as they do still, 

 with disastrous results to fauna and flora. In many cases, the 

 waning away of an order, or even of a class of animals, may be 

 associated with the appearance of some formidable new com- 

 petitors ; for Cuttlefish would tend to exterminate Trilobites, 

 just as man is rapidly and often inexcusably annihilating 

 many kinds of beasts and birds. Apart from the struggle 

 with competitors, it is probable that some stereotyped 

 animals were unable to accommodate themselves to some 

 change in their surroundings, and also that some fell victims 

 to their own constitutions, becoming too large, too sluggish, 

 too calcareous, in short — too extreme. 



