. Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean . he BernardinoPass ; and on the north side of the Desert, opposite Deep Well. The position of the principal of these accumulations will be found upon the geological map ofthe Desert, where they are indicated by the finely dotted spaces. The most formidable and extensive accumulation is that between Pilot Knob and the constitutes what has been known as the Sand-hills of the Desert; the other localitiesbeing either insignificant,
. Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean . he BernardinoPass ; and on the north side of the Desert, opposite Deep Well. The position of the principal of these accumulations will be found upon the geological map ofthe Desert, where they are indicated by the finely dotted spaces. The most formidable and extensive accumulation is that between Pilot Knob and the constitutes what has been known as the Sand-hills of the Desert; the other localitiesbeing either insignificant, or being in unexplored places. This accumulation of sand-hillsborders the emigrant road on the north side for several miles ; it is a part of a long crescent-shaped belt of sand, that extends from Pilot Knob to the vicinity of the Alamo. In passing from the Colorado towards the Pacific, the first sand-hills of this belt are seen atthe Indian village, overlying the upper terrace. Nearer Cookes Well the sand has pouredover the bank, as shown in the figure, so that it encroaches upon the road, and partially buries SECTION OF SAND-HILLS COVERINO THE S, Sand, drifting from the north ; C, Clay and sand of the bank or terrace. some of the mezquite bushes. Beyond Cookes Well the sand falls over the terrace in a similarmanner. In fact, the southern extent and range of the sand-hills of this belt is determined by,and coincides with, the bank or terrace constituting the margin of the upper or higher plain ofthe Desert. 31 F 2 42 GEOLOGY. It is from the surface of this gravelly plain that the sand is derived ; it is swept from it bythe strong winds, and travels along until the force of the wind is broken or changed by somenatural obstacle. At such places the sand is dropped, and soon becomes heaped up into undu-lating ridges, which simulate the billows of the ocean by their wave-like contour. All theprincipal sand-hills appear to have accumulated upon the edge of this terrace ; and
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