nnum. The chief use to which slate is put is for covering buildings, and for this purpose it is better than any other known material. It is also us

in the strata close above the Metamorphic rocks, near the beginning of what is called th

difference between slate and shale, for instance, is not one of ingredients, but of the process by which the ingredients are put together. All of the sedimentary rocks are formed by a deposit of sediment from the water on the bottom of the ocean. At one period the floods ha

ngest dimensions in line with the plane of cleavage. Shale in color looks like slate, and an analysis of the material of which it is formed shows that shale and slate are both made from the same. There is, however, a

mixed, and subject it to a very great pressure, and then examine the piece that has been submitted to pressure under a microscope and compare it with a piece of the clay after it has been thoroughly mixed, but has not been submitted to pressure, you will find that the two are very different in structure. The pressed clay will show that the particles of which it is made up have all turned, so that their longest dimensions are in a line

changed the lines of pressure upon this material and the pressure is so great that a rearrangement of the particles of which the slate is

ss it in more common language, the grain has been changed. So that when it splits up it runs crosswise of the original layers as the water deposited

we find that lines of cleavage have been established, and that the particles have been rearranged so that their longest dimensions are all in one direction, which coincides with the cleavage lines. If we should now take this same piece of clay and subject it to a pressure at right angles to that of the first experiment we should find that the lines of cleavage had also changed

cope. Thin layers of slate have been made, the same as with limestone and chalk, so thin that the light would readily pass through it and that an examination of the particles could be re