Every one knows the difference between the appearance of a new house and that of an old one: in the former the stones of the walls are clean and sharp, in the latter they have a weathered, time-worn look. In graveyards the headstones recently put up have their inscriptions sharp and clear; the older stones have their surfaces pitted, and the letters carved on them are indistinct. Compare the old carvings and tracery on the outer walls of our cathedral, made hundreds of years ago, with the clean-cut masonry of new buildings which stand near it, and you will see that stones decay with time and moulder away; they crumble into dust under the winter’s frost and rains and the heat of the summer sun. So it is with all the rocks of which the surface of our islands is made up. Year by year they moulder away. The dust or earth into which they break down forms a soil in which plants take root and grow. The plants push their root fibres downwards, helping to open up the cracks in the rock; and when these roots die and decay their substance mingles with the soil, giving it that black colour which marks old fertile soils that have long been cultivated. Under the soil lies the subsoil—that is, rock which is half decayed and partly broken up. In course of time it will become as fine as the soil itself; for the subsoil gradually changes into soil. In wet weather the rain, and in dry weather the wind, carry away the fine particles of earth from the surface of the fields, and would sooner or later take away all the fertile soil; but the continual action of the weather on the subsoil supplies fresh material. Hence, while the old soil is constantly being removed, new soil is forming to take its place. As we see in the quarry, under the soil and the subsoil there is rock. This is true of all parts of our country; there is a rocky skeleton beneath the thin layer of fertile soil which supports the plants and animals. In the rocky skerries which are common along the shores we see the nature of the rock-built framework of the islands. If the soil and subsoil were swept away, as the waves have swept it from the skerries, it would be plainly seen that the islands are built up of rocks. All the rocks of our islands, almost without exception, were laid down under water. They consist of three different substances. One is sand, in small rounded white or yellow grains. Another is clay, dark gray in colour, very close grained and soft. The third is lime.