188 
FINDING NATURE’S TREASURES 
“Yes,” continued Uncle Jack, “that was when this 
snail was alive. This kind of snail lived only in the 
ocean. Wherever you find their pictures in the rocks, 
you may be sure that the ocean was there a long, long 
time ago.” 
“I don’t see how their pictures could get in the rocks,” 
said Buddy. 
“This rock was soft when the snail was alive,” ex¬ 
plained Uncle Jack. “The snail died and its shell lay on 
the bottom of the ocean. The shell became covered with 
sand and mud. Slowly the sand and mud became harder 
and harder. Mud squeezed inside of the shell, and that 
became hard, too. Now, you can see just where the shell 
was, and what it looked like.” 
“This must have been a big snail,” said Buddy. “I 
never saw one alive the size of this one. It would cover 
your hand.” 
Uncle Jack continued, “There were many large crea¬ 
tures living on the land and in the water then. Some of 
the animals were very much larger than elephants. Some 
of the snails were as big as a large head of cabbage. 
People find the pictures of many birds, insects, fish, 
plants, and trees pressed into the rocks. Sometimes the 
real bones of animals that lived then are found. These 
rock pictures and bones are called fossils, and they tell 
us stories of what the earth was like when they were 
alive. Men dig them out of the rocks and put them in 
show places called museums. We can go to museums and 
