16 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
Some General Deductions.—The analytic results set forth in the above table 
and in the one given below show that the sand is mainly composed of grains of 
calcium sulphate derived from crystalline gypsum. Silica and also silicate of 
iron and aluminum are present in small amounts. Insignificant quantities of 
soluble substances such as chloride (probably of calcium) may also be detected. 
The sand is free from nitrogenous matter, except such minute amounts of 
animal débris and excreta as have already been referred to. 
Percentage Composition. (Sand dried at 30° to 35° C. and at 110° to 120°C.) 









fe If. Average. Average. 
Paths dew tts Fees Pick. 
CaO). addawick se 2 ees SF oe a ee 30.4 Sin 2 30.8 38.5 
SO, sia ks «ost Rake side ate 1 ie ae 44.5 43.9 44.2 Bout 
BIOs. marie iaes Sapo eine «oe Ce ee 2.8 a0 ee | 3-4 
Al,O; \ 
fe, |<) | tear cu 6 0.4 0.4 0.4 0.5 
FO ys seal acre ta ¢ } me wy eee ae sigitalan 20.8 20.8 Bek 
Traces: O, Cl, Na, PO, (by difference) >... ie 1.4 
Calcium sulphate; CaSO,.2H,OF (ig ee 95.8 ee 
Calcium sulphate, anhydrous............. 455.0 93.6 
ees. 


It is very evident that the sand readily dissolves in water. Every rain, no 
doubt, dissolves some of it and the waters in the district from which the sand was 
obtained must be heavily charged, probably to the saturation-point, with gypsum. 
On the evaporation of such water, in the sand or in pools, calcium sulphate is again 
rapidly deposited. 
SAMPLE II. LocALity: SAMALAYUCA, CHIHUAHUA, MEXICO. 
General Description.—A composite sand, yellowish to light-brown in general 
appearance. No crystals were detectable in it. The grains were of irregular 
shape, but of fairly uniform size. None were any larger than the small, uniformly 
sized ones of SampleI. The grains were angular, with the edges showing the effects 
of erosion. Glassy and brownish grains predominated. Others with the following 
colors were to be seen: Amethyst, dull white, dirty yellow, purple, black, and red. 
All of this sand passed readily through the sieve used onSampleI. Noextrane- 
ous matter was found in it. 
Qualitative Data.—The sand was very resistant to the solvent action of water, 
alkalies, and acids, scarcely anything dissolving in these fluids, hot or cold. The 
colored grains were somewhat reduced in number after treatment with acid, the 
solution in hydrochloric acid having a yellowish tinge. The sand fused with sodium 
carbonate with great difficulty. The fused mass was bluish-gray in color. On 
ignition the sand lost only a slight amount of water. It became pink and yellowish- 
red in places, but did not fuse, even in platinum over a blowpipe. Carbonic acid 
gas could not be obtained from it on ignition, so that the sand is obviously entirely 
