The valley immediately east of the Rocky mountain range is composed of an extensive accumulation of sand, seemingly the debris of the mountains. To an unknown depth, the soil is made up of rounded fragments of granite, varying in dimension from a grain of sand to a six pound shot. This accumulation has evidently been washed from the mountains, and slopes gradually from their base. The small particles derived from the quartzose portions of the primitive aggregates, being least liable to decomposition, have been borne to the greatest distance, and of these the eastern margin of the great sandy desert is almost entirely composed; the central portions are of coarser sand, intermixed with particles of mica and feldspar; nearer the mountains, boulders and pebbles occur abundantly, and at length cover almost the entire surface of the country. In many other respects besides geological structure, the Apalachian range of mountains differs from that we have just been considering. The whole of their eastern front is composed of primitive rocks, comprehending both the granitic family and its associated strata of clay-slate and limestone. In New England, rocks of this class constitute the seacoast, and with some exceptions extend inwards towards the St. Lawrence. South of the Hudson, the edge of the primitive follows the general contour of the mountains, at a variable distance from the sea to their termination, and until it meets more recent deposits at the extremity of the mountain range. The breadth of this primitive belt is very unequal. In passing through the states of Pennsylvania and Maryland, it occupies but a small part of the country; in Virginia it increases in breadth, and proportionably in height, composing the greatest mass as well as the most elevated points of the mountains in Georgia and North Carolina. Besides this range, there is a great mass of primitive on the west side of lake Champlain. In general, the primitive rocks run from a north and south to a north-east and south-west direction, and dip generally to the south-east at an angle of more than forty-five degrees with the horizon; their highest elevation is towards their north-western limit. The mountains of this formation consist generally of detached masses, with rounded flat tops and a circular waving outline. Granite in large masses constitutes but a small part of this formation, and is found indifferently in the plains and on the tops of mountains. Gneiss extends perhaps over a half of this formation, and includes in a great many places beds from three to three hundred feet thick. These beds are mixed, and alternate occasionally in the same gneiss with the primitive limestone, the beds of hornblende and hornblende slate, serpentine, magnetic iron ore, and feldspar rocks. In short, there are scarcely any of the primitive rocks that may not occasionally be found included in the gneiss formation.