Young Folks' Library, Volume XI (of 20) - Wonders of Earth, Sea and Sky by Various
page 45 of 355 (12%)
page 45 of 355 (12%)
![]() | ![]() |
|
I. _Flint Rocks_; II. _Clay Rocks_; III. _Lime Rocks_. This is not a book in which it would be wise to go closely into the mineral nature of rocks. Two or three leading thoughts may, however, be given. Does it not seem strange that the hard and solid rocks should be in great measure formed of the same substances which form the thin invisible air floating around us? Yet so it is. There is a certain gas called Oxygen Gas. Without that gas you could not live many minutes. Banish it from the room in which you are sitting, and in a few minutes you will die. This gas makes up nearly one-quarter by weight of the atmosphere round the whole earth. The same gas plays an important part in the ocean; for more than three-quarters of water is _oxygen_. It plays also an important part in rocks; for about half the material of the entire earth's crust is oxygen. Another chief material in rocks is _silicon_. This makes up one-quarter of the crust, leaving only one-quarter to be accounted for. Silicon mixed with oxygen makes silica or quartz. There are few rocks which have not a large amount of quartz in them. Common flint, sandstones, and the sand of our shores, are made of quartz, and therefore belong to the first class of Silicious or Flint Rocks. |
|