Mingling its echoes with the eagle's cry, And with the sounding lake, and with the moaning sky." ،، Not far east from here rises a stupendous dune of sand, or, rather, a promontory of uncemented sand and clay, capped by a shifting dune. The grinding action of the waves has pulverized a cubic mile of sandstone and superincumbent drift, which has been strewn over the lake's bottom. The nervous wind-gust has wrested it from the water, and made it a plaything of its own. Dried by the sun and air, it has been driven inland till the forest is submerged, and a shining promontory called Grand Sable lifts its forehead four hundred feet above the lake-a landmark for the mariner and a marvel to the lover of Nature. CHAPTER IX. DISCOVERY OF THE PROGRAMME. THE reader will have observed that the primal or Pots dam sandstone has been traced all around the circuit of the central United States. There is no doubt that it underlies all the region embraced within the circumference of its outcrop. Indeed, at Columbus, Ohio, an artesian boring has probed the crust 2000 feet and more, and found this sandstone in its proper place. At Lafayette, in Indiana, Louisville, in Kentucky, St. Louis, in Missouri, and Chicago, in Illinois, similar deep borings have been executed, and the succession of strata, as far as the borings extend, hast been exactly such as geology expected; and there can not be a doubt, that wherever exploration should be made. throughout the wide extent of the area indicated, the Potsdam sandstone would be found occupying its proper position at the bottom of the Silurian series of strata. As the same formation has been upheaved, at intervals, along the whole distance to the Rocky Mountains, geologists have arrived at the conclusion that the entire area of the United States and Territories was, during the Lower Silurian Age, the bed of a comparatively shallow sea. This conclusion leads to a generalization of the highest interest. How came the central area of the North American continent a basin of shallow water? We can only infer that, at this early period, the Alleghanies on the cast, and the Rocky Mountains on the west, had already begun to be lifted above the general floor of the ocean. The United States were an immense continental lagoon—a subma rine plateau, such as now exists in the North Atlantic, upon which the telegraphic cable has been laid. The outline of the continent was consequently marked out while yet in embryo. The foundation of the Alleghanies was laid ages before the superstructure rose above the waves, and exposed to the light of day the predestined trend of the Atlantic coast of our country. But we trace the development of this idea back to a still remoter period. Note the trends of the primeval ridge (Figs. 19 and 39) which still lies thrusting its angle down into the northern notch of the "great lakes." "Northeast and northwest" was the language of that earlyuttered decree which foredetermined the shape of the continent which was destined to become the "land of the free." That primal ridge was its earliest germ. Successive annexations to this germinal continent have been uniformly toward the southeast and southwest. This primitive ridge was not alone an early prophecy of the trends of our present coast Fig. 38. Section across the Continent of North America. San Francisco. Mount Diabolo, 3770 ft. Sierra Nevada, 15,000 ft. Humboldt Mountains, 7473 ft. Great Salt Lake, 4200 ft. Utah Lake, 4500 ft. Green River Valley, 3823 ft. Sierra Madre. Pike's Peak, 12,000 ft. Ozark Mountains. Mississippi River, Cairo. Cumberland Mountains, 2000 ft. Black Mountain (Blue Ridge), N. C., 6476 ft. Cape Hatteras. lines. In its upper angle lies Hudson's Bay, whose place was designated as soon as it became the bottom of a submarine valley. The southern slope of the ridge became the water-shed which was to supply the great lakes and the St. Lawrence. The St. Lawrence finds its outlet to the ocean in a valley parallel with the ancient ridge. The peculiar notch from Georgian Bay to the head of Lake Erie, and thence to the Niagara River, is conformed to the sal Fig. 39. Hydrographic and Orographic Outlines of North America. ient angle of the same ridge. The "great lakes" themselves are but links in the vast chain of lakes extending to the Northern Ocean, accumulated in a valley inclosed by the western branch of the continental nucleus on the one hand, and the occidental ridge of the continent on the other. The Mississippi pursues its course along the bottom of the depression between the Appalachian and Rocky Mountain ridges, while the McKenzie-the Mississippi of |