THE STORY THE SEA TOLD i6i 



transformed into solid rock. While the shores 

 formed sandstone or slate, because of the ma- 

 terial of which they were composed, the ma- 

 terial at the bottom of the sea formed lime- 

 stone because it was composed mainly of lime 

 from the myriads of tiny shells and skeletons 

 of marine animals. 



In addition to shells these petrified portions 

 of the ocean's bed contain corals, worm-tubes, 

 sea urchins and various other forms of marine 

 life, many of which no longer exist. Some- 

 times these specimens are crowded together 

 into a mass in which the various animals are 

 scarcely distinguishable, while at other times 

 they are separated and are beautifully pre- 

 served. As a rule the fossils are much harder 

 than the surrounding rock, and very fre- 

 quently the softer portions have been decom- 

 posed and worn away through exposure to 

 the weather for countless ages and the shells 

 and similar fossils have been left free in the 

 earth, clay or sand. When this occurs one 

 may often find specimens of shells or sea- 

 urchins so perfect in every detail that it is 

 difficult to believe they are made of solid 



