THE HARDENING OF ROCKS 



signs of life begin to appear. We may see in them to-day 

 the first fossils. A fossil means literally a thing dug up, 

 and was a term applied at first to all kinds of mineral sub- 

 stances taken out of the earth. We use the word now 

 exclusively for the remains of plants and animals em- 

 bedded in any kind of rock. In later chapters of this 

 volume a good deal will have to be said about fossils, and 

 of the way in which they tell us the kind of life that 

 existed when they were first sunk in the rocks where now 

 they are found, and how also they give us information 

 about the climate and the distribution of land and sea, of 

 lake and of river, in those eras far " in the backward and 

 the dark abyss of time." 



For the present, however, we may concern ourselves with 

 the condition of the earth and its rocks in Proterozoic 

 times, observing merely that the remains of animals 

 which we find there are of an order (Crustacea) which 

 shows that life had progressed a good deal from its earliest 

 beginnings in the age when the rocks containing these 

 Crustacea were laid down. After these rocks had been 

 deposited they were subjected to many influences of which 

 we have only dim conceptions. In a previous chapter we 

 have compared the layers of the undermost and harder 

 rocks of the earth to the lines on a page' of this book as 

 they would appear if the pages were crumpled up into a 

 ball. Sometimes the beds of solid rock have been so dis- 

 torted that they look like waves of the sea ; sometimes 

 they have been completely overturned ; hardly ever have 

 they been suffered to lie down flat. More than that has 

 happened to them. Their very nature has been changed. 



