You cannot examine many of our Orkney flagstones carefully without finding fossils. The most common are scales and bones of fishes. In the rock these often appear as coal-black specks. When a fossil has weathered for a long time, as in a stone dyke or on the seashore, it often becomes bright blue, like a splash of blue paint. Sometimes whole fishes are found in the gray flagstones, with every fin and every scale perfect. Of course you will not find these every day or every year, but there are many quarries in Orkney where you may get them occasionally. When the quarryman uncovers a bed of rock, he often finds it sprinkled over with great numbers of fossil fishes. We can picture to ourselves that, at some time long gone by, when these flagstones were being laid down in the old Orcadian lake as sheets of sandy and muddy silt, the fishes were suddenly killed by a volcanic eruption, or by a period of drought, and their dead bodies covered the muddy bottom for miles. Fresh mud then came down and buried them, and preserved their remains. In process of time their bones and scales were changed into the pitch-black substance which we now find in the rocks. But we can still see that these specks and scales are really parts of fishes. If we examine them under the microscope, we find that they have all the marks of structure that the same parts of certain fishes have at the present day. In almost every parish in Orkney there is at least one quarry which contains good fossils, and there must be many others which we do not yet know of. But no person who knows what a bit of fossil fish is like need search very long among the flagstones of the shore without finding a scale, a jaw bone, a tooth, or other relic of the fishes which lived in Orkney at the time the flagstone muds were gathering. A heap of stones thrown down by the roadside, for building a dyke or for mending the roads, often contains fragments of dozens of fishes. It is not difficult for us to picture what these fishes were like when alive. Some of them were about the size of sillocks or herrings, others were as large as a big cod. They had scales all over their bodies, and fins, supported by bony rays, just like living fishes. But though many of them were of the same shape and general outline as a trout or a herring, they differed from these in many ways. Their scales were often hard and bony, with a smooth, shining outer layer of enamel like that which covers a tooth. Those fishes are called _ganoids_. On their heads they had bony plates with the same hard covering, often showing ridges and furrows, knobs, and other markings. You may see these beautifully preserved in many of the fossil bones which occur in the gray and blue flagstones. Those fishes belong to species which are no longer living on the earth’s surface, but closely allied kinds of fish are still found in a few rivers in Africa, America, and Europe. The royal sturgeon is one of these.