These Z-shaped rock folds were made by the crumpling up of the crust as the centre, cooling, shrank away. They are to be seen near the east end of Ogden Canyon, Utah. The black lines were added to the photograph in the offices of Uncle Sam's big department of geology at Washington, to show clearly just where the rock runs. ] You may often have noticed a banded effect in marble. My, what power it took to do that! Pressure we can't realize. Pressure from above so great that it made this marble spread; moulded it like clay in the hands of the potter; the same kind of force that flattened out the pebbles referred to in Chapter V. This is called "rock flow," and how plainly the marble shows the flowing movement. I always think what the weather people call "stratus" clouds, look as if they were made by long strokes of a painter's brush; and this marble has the very same flowing lines. Such cloud pictures in marble are made where deposits of other kinds of rock have been interlaid with the deposits of limestone which afterward changed to marble, and it is where these bands are folded or bent that we have set down for us the story of the mountain folds. Those gossamer effects and the little white clouds spinning out and fading into the general mass of the marble, how delicate they are! Yet it took a force that made the earth quake to put them there. The more we know of the strange and fearful things that happen in times of earthquake the more we can read between these filmy lines. They tell of the sides of mountains tumbling down and spreading their valleys with a chaos of broken stone; making cliffs where there were peaks and peaks where there were cliffs; changing the course of rivers; shifting whole forests on the mountainside and replacing them with grim walls and bastions of barren stone--all in the twinkling of an eye! THE EARTHQUAKES AND THE DELICATE FILMS It is by the crushing movements that made the earthquake that rocks are broken into confusions of cracks such as you often see in a thick glass window that has been broken. Then into these cracks come dissolved minerals from other rocks and harden into stone. In the marble one set of veins often runs right through another as if they had been inlaid. Then there may be other veins that cross both of these--no end of criss-crossings. The different sets of veins usually differ also in color and in grain, and even have different kinds of mineral in them. With a good hand-glass you can see this difference in texture. [Illustration: WHEN THE EARTHQUAKE TAKES ITS PEN IN HAND