In another instance it is said that a human skull was discovered in Calaveras County, Cal., at the bottom of a shaft which had been sunk one hundred and thirty feet below the surface. It was found deposited in a bed of gravel with other organic remains, and beneath the eighth distinct geological layer of earth and gravel, where it must have lain, according to the estimate of Professor Whitney, the geologist, for a period of at least one hundred thousand years. This remote antiquity of man is also confirmed by discoveries in every part of the world of the fossil remains of domestic animals as well as of man, including implements of human invention, such as flint arrow-heads, stone axes, war-weapons, cooking-utensils, in localities which preclude the idea of their belonging to an age that has a written history. It is not unfrequent that fossil remains of human bones and of animals are found embedded in the coral-reef limestone of Florida. In fact, says Professor Agassiz, the whole peninsula of Florida has been formed by successive growths of coral reefs and shells; he estimates the formation of the southern half of the peninsula as occupying a period of one hundred and thirty-five thousand years. The sea contains ingredients which feed innumerable animalcula, especially the polypes, or coral-builders, which have the power of secreting calcareous matter. These myriads of noiseless architects are ever busy in building for themselves fairy temples in the depths of the ocean, of the most delicate and beautiful workmanship, and in erecting pyramids and islands, and in extending continents. In the mean time there are other agencies of a very different character continually at work, modifying the earth's surface, and preparing it for sustaining a still higher order of vegetal and animal life. As a result of these agencies, especially the volcanic, it often happens that serious calamities befall the human family. In the course of a century, not less than two thousand volcanic eruptions occur on the globe, equal to twenty a year, or one every eighteen days. The whole number of volcanoes known to be active at the present time exceeds three hundred; and doubtless many times that number have long since become extinct. In Europe, Asia, Africa, and America, there are extensive tracts or belts of country which are volcanic in their character; and especially is this true of the entire American-Pacific coast, and the ocean-bed adjoining it. Often have long lines of this coast been elevated or depressed many feet, as if the whole continent were afloat, and tossing like a ship on a stormy sea. Neither in the past, nor in the present, has the earth seemed to rest on a sure foundation. Even in apparent security there is no positive safety.