42 HANDBOOK OF NATURE STUDY 



24. How the Rocks were made. 



To-day I will try to answer your questions about " How 

 the rocks came to be.' 7 They were formed or deposited in 

 water just like the bottom lands and sand banks we visited. 

 You noticed that the soil grew more compact as we dug 

 down, because the soil above, so to speak, pressed it. Deep, 

 heavy waters pressed on the rock above, and the upper 

 layers also pressed on the lower. This pressure was one of 

 the forces which made rock of the fine mud or sand. In 

 many rocks there is also some cementing material which 

 holds the particles together, as lime cement binds the sand 

 grains in mortar; and some rocks have been burned hard 

 like brick. Most stratified rocks were formed on the ocean 

 bottom, by mud or sand washed into them by rivers and 

 waves. How do we know that ? Much of this stratified 

 rock extends in almost horizontal layers over thousands of 

 square miles, and in it are often found fossils of marine ani- 

 mals. In some places stratified rock has been formed in 

 large fresh-water lakes. Whenever you find distinctly strati- 

 fied rock extending over large areas, you may take for granted 

 that it ivas deposited by water as mud or sand. 



I know what several of you are going to ask me now. 

 You want to know where all this mud and sand could come 

 from. Some day I shall tell you about that. You may find 

 something about it in your geographies or in some simple 

 treatise on geology. 



If -you can visit different kinds of stratified rock, study 

 it closely. Can you easily break ib with hammer and 

 chisel, or is it so hard that it will scratch glass ? Does it 

 seem made of grains of sand, or does it appear like hardened 

 clay ? If you find many fossils in it, you most likely have 

 a limestone. This rock has the peculiar " limey " taste and 



Observations Find the seeds of grasses. 



