Common limestone is almost entirely the product of minute animals[4] which lived in early geologic times. Ages before the Romans drove piles into the Thames, or the first hut was erected on the banks of the Seine, these little creatures laid the foundations which underlie London and Paris. They built the rocky barriers which gave to England the name Albion, derived from the white cliffs along her shore. It is a suggestive crumb of comfort for little folk, that the great tasks in the building of our earth have been performed by the smallest creatures. The wide distribution of limestone is shown from the fact that it is found to be an ingredient in almost all waters. It is readily dissolved, as is seen in the numerous caves which are found in limestone regions. When limestone is heated, the carbonic anhydride[5] is expelled, leaving quicklime. All are familiar with the manifold uses of this material. United with sand, it forms a silicate of lime, called mortar, which becomes harder with age. In the old stone mill[6] at Newport, R. I., which is of unknown antiquity, the mortar in some places actually protrudes beyond the stones, showing it to be more durable than the rock itself. The catacombs of Rome were excavated in a very soft kind of limestone, called calcareous tufa. Sulphate of lime, also known as gypsum and plaster of Paris, is widely distributed. One beautiful variety is called satin spar, and another alabaster. Great quantities of sulphate of lime are quarried for use in the arts and for agricultural purposes. Dr. Franklin was one of the first to discover its value in connection with crops, and is said to have sown it with grain on a side hill, so that when the wheat sprang up, observers were surprised to see written in gigantic green letters, “Effects of Gypsum!” I suspect he got the hint from Dr. Beattie, who sowed seeds so that their flowers formed the name of his son, to prove to the boy the existence of a God, from evidences of design in nature. ALUMINA—Al₂O₃. This material is found both alone and in combination with silica. It forms an important ingredient in alum. Crystallized, it furnishes some of our most rare and beautiful gems, the color of which depends upon the metal combined with them. The ruby is red, the emerald green, the topaz yellow, the sapphire blue. Slate rocks consist largely of this material, and clay is a compound of alumina with siliceous anhydride. Among the first earthy substances utilized by man was clay. We find remains of pottery even as far back as the stone age[7]. The ingenuity of man seems to have been displayed constantly and successfully in the ceramic[8] art, the art of making pottery. Note the accounts given by Prescott, in his “Conquest of Peru and Mexico,” and the Cesnola collection of Cypriote remains[9] exhibited in the Metropolitan Museum in New York City.