34 LIFE IN THE PRIMITIVE OCEAN 



hard parts were developed, and we begin to find these 

 preserved as fossils in the rocks. Some began to 

 form coats of lime (shells), and the great family of the 

 Molluscs (mussels, cockles, oysters, etc.) spread over 

 the floor of the ocean. Natural selection is very 

 useful in explaining protective parts of this kind. 

 Others had their bodies drawn out into sections, with 

 a tough coat on each section (crabs, water-fleas, 

 shrimps, etc.). Others had long wriggling bodies 

 (worms). The seas now teemed with life, and there 

 was a mighty struggle for food and safety. The less 

 fit perished, age by age. Organization crept higher 

 and higher. 



But I will close this chapter with an illustration of 

 the way in which the geological changes which w^ere 

 going on all the time influenced the living things, 

 even in the water. I have said that the land was 

 rising above the water, as the ocean sank into deeper 

 beds. We have strong reason to think that these 

 changes were often acute and violent. The man who 

 says that the secret of progress is "evolution, not 

 revolution," may be talking very good social philo- 

 sophy — I have nothing to do with that — but he is not 

 talking science, as he thinks. In every modem 

 geological work you read of periodical "revolutions" 

 in the story of the earth, and these were the great 

 ages of progress — and, I ought to add, of colossal 

 annihilation of the less fit. 



We will see some of these later. Here I refer to 



