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 It is certain that algarrobo played a great réle in the food supply of the former inhabitants of the Desert of Atacama, as it did on the other side of the mountains. Fruits and many objects made of algarrobo wood were found by Eric Boman in the graves of Calama.

For several miles in the piedmont stretch our trail crossed dry baked mud flats where the flood waters are impounded in shallow reservoirs according to the natural depressions of the ground. The tops of the blocks between the mud cracks are curled upward and break into thin flakes along the bedding planes as the mules’ hoofs dislodge them. A strong wind had been blowing from the sea during the afternoon, and it had drifted sand from near-by sources over the mud-cracked sur- face, filling in the spaces between the cracks and the curled edges of the plates. It is by such means that the geologist, studying mud layers visible in the rocks formed in remote geo- logical ages, determines past climates and other conditions of formation in places that now may have plenty of moisture.

Beyond this point we rode farther into the piedmont and entered more broken country where we experienced great diffi- culty in keeping the trail, for each traveler had apparently taken his own route. [From the summits of the ridges between the shallow valleys we could now look over the whole width of the nitrate pampa and see the low hills of the Coast Range out- lined against the dark haze, the top of the fog bank, that hangs over the edge of the Pacific. The desert trail where it crosses the salars appeared broad and white in contrast to the darker yellow and brown of the untraveled pampa and could be seen for a distance of at least fifteen miles. The bright yellow light of sunset gave place to purples that seemed almost to creep out of the mountains and the sky above them until we could see at first faintlyand then more clearly the lights of the nitrate works at Alianza on the western border of the nitrate fields. There