“No; some sandstone, especially that lying near the surface of the ground is soft, and the grains are loosely held together, and are large and distinct. Other sandstone has been pressed together into a mass nearly as hard as marble or granite. Flagstone is sandstone laid down in thin beds, and capable of being readily split into flags or slabs. Freestone is a soft sandstone which is capable of being readily cut in any direction; buhrstone is a particularly hard, rough sandstone, of which grindstones for mills are made. Roll yonder great, rough stone here. What do you think of it?” “It looks like plum-duff,” said one of the pupils, “only the plums are rather large and numerous, and the dough is very hard and scanty.” “It is conglomerate,” said the teacher, “and conglomerate differs from sandstone in the size of its grains. Where sandstone has tiny quartz crystals for grains, conglomerate has pebbles, fastened together with mud hardened like cement. Coarse sandstone closely resembles fine conglomerate. Another kind of sandstone is called greywacke. Greywacke often exhibits the ripples and sun-cracks of the ancient beach. In greywacke the grains are rounded, or nearly rounded, are uncolored, and are cemented together by a very hard paste of chalk or silica. If you look at a piece of greywacke you might think it a portion of igneous or fire-made rock, it is so fine and hard. You must remember that rocks which have been--let us say, well cooked, by the earth’s internal fires, are very hard and compact; they have been fused together and then cooled, and the process has made them very strongly coherent. But sandstone in all its varieties is a water-made, not a fire-made rock. These water-made rocks are called fragmental, while fire-made rocks are termed igneous. Whatever heat has been applied to sandstone has served only to melt and harden the fine cement, but has not been sufficient to fuse the grains. The term fragmental, as applied to rocks, means that the parts are easily divisible, and are largely individual and fragmentary. Clay rocks are fragmental, and so are limestone rocks. There are also a few of the fragmental rocks which have been very greatly heated, and indeed were once flung out of volcanoes in a red-hot or melted state. But as they are in a loose condition much like cinder and ashes, they are classed among the fragmental rocks. Among these are tufa, breccia, volcanic conglomerate, and two or three others.” “It needs much learning to read so much from a few footprints in sand,” said one of the pupils, as they rose to go homeward.