peror Augustus, which gave its name (Adriatic) to the gulf, is now more than twenty miles inland. серией 28. The detritus of the Amazon does not form a delta at its mouth, but is swept by ocean currents, and distributed partly in the ocean, where it is discernible three hundred miles from the mouth of the river, and partly to the coast of Guiana, where it has formed an immense alluvial deposit. When the matter deposited at the mouth of a river has not accumulated sufficiently to rise to the surface of the water, it is called a bar. Such a bar, called "the Overslough," is formed a few miles below Albany, in the still water caused by the meeting of the waters of the Hudson with the tide from the ocean. The attempt to remove this obstacle to navigation by contracting the river, tended only to increase the velocity of the current and thrust thesia. bar farther down the river. 29. In addition to the materials conveyed mechanically by water, extensive deposits are made by springs. The waters of many springs are charged with carbonate of lime, which is deposited when the water issues from the rocks. Substances deposited in such water become incrusted with limestone. This is not petrifaction, since the substance undergoes no change, but is simply enveloped in the incrusting mineral. Fig. 8. Incrusted Twig. The preceding cut cxhibits a stick thus incrusted. Many such springs in northern Ohio incrust the mosses growing in their vicinity, furnishing beautiful but frail specimens. The loose, porous rock formed by these deposits is called tufa; the compact is called travertin. Beds of these, some miles in length and several hundred feet thick, are formed by springs in France and Italy. At San Filippo, in Italy, medallions are made by conducting the water into moulds; the deposited matter filling the mould, presents a marble cast of the figure. The beautiful alabaster of Tabreez, in Persia, has the same origin. 30. Deposits of silicious matter are made by hot springs. In the Azores islands hot springs, rising through volcanic rocks, deposit large quantities of silicious sinter, as it is called, incrusting with beautiful crystalline scales all substances with which their waters come in contact. But the most remarkable hot springs are the Geysers of Iceland, whose circular basins are lined with the silica of their waters. Some springs deposit iron ore, common salt, asphaltum or mineral pitch, (Seneca oil,) &c. 31. Another mode of action of water is exhibited in land slides. In the year 1806, after a rainy season, the Rossberg, a mountain in Switzerland, was undermined, and a mass of two thousand millions of cubic feet precipitated into the valley, forming hills two hundred feet high, and destroying several villages. Land slides have also occurred from a similar cause in the White Mountains, and near Troy, New York. The banks of the Lake and the Cuyahoga valley in the city of Cleveland, are frequently subjected to the same process of g degradation, as shown in figure 9. The water which strata of gravel and 32. Glaciers and icebergs-water in a solid form-are very influential in effecting changes upon the surface of the earth, and their peculiar phenomena have recently attracted much attention on the part of geologists. Glaciers are immense bodies of ice formed in the valleys or on the sides of mountains, extending many miles, and remaining undissolved by the heat of summer. Fig. 11. Por 11412 tions of their mass are granular snow cemented by ice. They vary in thickness from one hundred to eight hundred feet, and have a very gentle slope. Their surface is very rough and often studded with conical masses of ice, called needles. They are traversed by wide fissures pro Fig. 12. Glacier of Viesch, with medial and lateral moraines. Mastrations on this outfeel Fisa B. 244,249,281,260 subject duced by contraction in the winter. Each winter adds a new layer to their surface; the snow, however, disappears from their surfaces in summer, as regularly as from the surrounding rocks. Expansion, gravity, and the forms of the valleys, cause them to advance slowly down, sometimes even to the borders of cultivation. "The very huts of the peasantry," says Professor Forbes, "are sometimes invaded by this moving ice, and many persons now living have seen the full ears of corn touching the glaciers, or gathered ripe cherries from the tree with one foot standing on the ice." The surfaces and mass of glaciers abound with fragments of rocks which are often arranged in long lines, and are called moraines. The rocks over which glaciers pass are smoothed, scratched and grooved, by sand and angular stones forced forward by their enormous pressure. These striæ and grooves are parallel to each other, because the fragments which produced them are fixed in the bottom of |