ceous variety), perhaps from one to many centuries; coarse fossiliferous limestone, twenty to forty years; fine oölitic (French) limestone, thirty to forty years; fine oölitic (American) limestone, untried here; coarse dolomite marble, forty years; fine dolomite marble, sixty to eighty years; fine marble, fifty to two hundred years; granite, seventy-five to two hundred years; gneiss, fifty years to many centuries. Many of the best building-stones in the country have never yet been brought to the city.
Peroxide of Hydrogen.—Peroxide of hydrogen, though it was discovered in 1818, has only recently, by the aid of cheapened processes of preparation, come into general use. When pure, it is a colorless liquid, which in decomposing gives off four hundred and seventy-five times its volume of oxygen. Diluted solutions of it, kept in the dark at a temperature of not more than 80°, may be preserved for a very long time without decomposing. It is obtainable pure, in large quantities, and cheaply, in solutions of three per cent by weight or ten per cent by volume; and it has come into extensive use as a bleaching agent, for disinfection, household purposes, and the toilet. It is the really operative agent in air-bleaching on the grass, which has been in use from time immemorial, and is well adapted for bleaching substances of animal origin, in which chlorine agents often fail. In using it the substance to be bleached must first be carefully cleansed from dirt and oil. It may be applied as a bath in the shape of a weakly acid solution neutralized with a few drops of ammonia, or the substance may be dipped in it, and afterward slowly dried in the air. As the water evaporates, the concentration of the peroxide of hydrogen increases, and the bleaching goes on more energetically. Dumas and Pettenkofer have applied peroxide of hydrogen with much success and satisfaction to the cleaning of oil-paintings and engravings. This substance has recently been found to be one of the most valuable and effective disinfecting agents. In the household it has proved to be equal to the best of other known substances for purposes of washing and cleansing the person. It is adapted to the most tender skins. It has been pronounced preferable as a tooth-wash to all powders and to all other preparations which do not depend upon it. In bathing, with the addition of a drop or two of hartshorn, it quickly disintegrates and removes the dead skin without affecting the living tissue, except to make it more healthy and hardy. It is a salutary hair-wash, provided the hair has been prepared for it by previous washing with soap or spirit. Professors Alex. Classen and O. Bauer have found it a powerful agent in analytical chemistry. Die Natur.
Fact and Fancy regarding Fingal's Cave.—At the Montreal meeting of the American Association in 1882, Mr. F. Cope Whitehouse offered a paper on "The Caves of Staffa, and their Connection with the Ancient Civilization of Iona." The Committee on Papers, having heard Mr. Whitehouse in exposition of his views, and examined his maps and drawings, and the testimonials which he was able to produce from men of authority in science, adjudged that there were sufficient merit and originality in his paper to justify giving it a hearing. The article was also regarded by us of enough interest to be given to the readers of "The Popular Science Monthly" in December, 1882; and a summary of it was published in "Notes and Queries," December 28, 1883. In it the author, regarding the situation of the Island of Staffa, which is shown in the map, the character of its rocks, 
the form of Fingal's Cave, and the shape and direction of its exposure, concluded that it was extremely unlikely that the cave could have been hollowed out by the natural action of the waves, and suggested the question whether it might not have been artificially excavated. The paper has not yet been adequately an-
