120 
GEOLOGY. 
specimens of silicified wood. It occurs in great abundance, lying loose on the surface, and in 
places, tons of it could be collected from an area of one or two acres. 1 
In one of the slight gullies, or depressions in the surface of the plain, about half way between 
1 For a description of a specimen of the wood, see Appendix. 
examined the sandy and gravelly surface near this camp, and found that nearly all the grains 
of sand were much rounded. Lying down close to the surface, I was able to pick up a great 
number of the grains of different colors, and found them to be rounded fragments of quartz 
crystals, chalcedony, carnelian, agate, rose-quartz, and a green mineral, probably chrysolite. 
The spherical form is undoubtedly produced by the constant attrition of the grains as they are 
driven before the wind. 
December 13 .—Alama Mocho to the Big Lagoon .—Soon after leaving the Alamo Well we 
descended to the level of the hard clay, which forms a perfect plain without vegetation. The 
small shells, already noted, were very abundant. One or two small sand-hills—the accumula¬ 
tions about an old mezquite bush—were seen. We arrived at the margin of the Big Lagoon in 
the evening, and experienced a very high wind, which drove the sand and dust before it in 
clouds, and partly filled the tracks made by the wagon wheels. The sand moved along near 
the ground with a rustling sound, but the finer particles of grit were elevated into the air and 
driven with blinding force. 
December 14 .—Big Lagoon to Carrizo Creek .—The wind blew violently during the night, and 
we found, after starting, that it had blown the sand into thin drifts across the trail, filling up the 
ruts and tracks. These little drifts were only two or three feet wide and from one to six or 
eight inches deep. On reaching the slope leading up to the mountains, I secured many fine 
