In the neighbourhood of Cincinnati there have been uncovered banks of stone accumulated along the border of an ancient sea. From the sides of granite highlands streams brought down the sand built into these oldest sandstone rocks. The fine mud which now appears as beds of slate was the decay of feldspar and hornblende in the same granite. Limestone beds are full of the fossil shells of creatures that lived in the shallow seas. Their skeletons, accumulating on the bottom, formed deep layers of limestone mud. These rocks preserve, by the fossils they contain, a great variety of shellfish which had limy skeletons. The sea fairly swarmed along its shallow margin with these creatures. We might not recognize many of the shells and other curious fossils we find in the rock uncovered by the workmen who are cutting a railroad embankment. They are not exactly like the living forms that grow along our beaches to-day, but they are enough like them for us to know that they lived along the seashore, and if we had time to examine all the rocks of this kind preserved in a museum we should decide that seashore life was quite as abundant then as it is now. The pressed specimens of plants of those earliest seashores are mere imprints showing that they were pulpy and therefore gradually decayed. Only their shape is recorded by dark stains made by each branching part. The decay of the vegetable tissue painted the outline on the rock which when split apart shows us what those ancient seaweeds looked like. They belonged to the group of plants we call kelp, or tangle, which are still common enough in the sea, though the forms we now have are not exactly like the old ones. Seaweeds belong to the very lowest forms of plants. [Illustration: Crinoid from Indiana] [Illustration: _By permission of the American Museum of Natural History_ Ammonite from Jurassic of England] [Illustration: _By permission of the American Museum of Natural History_ Fossil corals Coquina, Hippurite limestone] The limestones are full of fossils of corals. Indeed, there must have been reefs like those that skirt Florida to-day built by these lime-building polyps. Their forms are so well preserved in the rocks that it is possible to know just how they looked when they grew in the shallows. One very common kind is called a cup coral, because the polyp formed a skeleton shaped like a cup. The body wall surrounded the skeleton, and the arms or tentacles rose from the centre of the funnel-like depression in the top. Little cups budded off from their parents, but remained attached, and at length the skeletons of all formed great masses of limy rock. Some cup corals grew in a solid mass, the new generation forming an outer layer, thus burying the parent cups.