10 Transactions Texas Academy of Science. [ 42 ] 
as well as it is, for I have already occupied too much space with the fore- 
going. 
Several years ago it was proposed to throw a dam across the Kio 
Grande river at El Paso, above which a reservoir with the enormous 
capacity of about 537,000 acre feet would be formed. This interna- 
tional dam was intended to remove all cause of complaint on the part 
of citizens in the El Paso valley, on both sides of the Rio Grande, who, 
year by year, have been obliged to abandon more and more of their irri- 
gated farms, some of which have been under cultivations for hundreds 
of years, probably since the Spaniards first found the Pueblo Indians 
practicing irrigation about the middle of the sixteenth century. Increas- 
ing irrigation along the upper reaches of the Kio Grande has caused 
the river to go dry frequently in the vicinity of El Paso, and the irriga- 
tors there have seriously suffered in consequence. During the time that 
surveys and estimates for this dam were being made under the general 
direction of Maj. Anson Mills, U. S. A., samples of the water were 
collected at frequent intervals and the quantity of silt present deter- 
mined gravimetrically. Between June 10 and July 28, 1889, one hun- 
dred and eighteen samples of water were collected. It was assumed that 
a cubic foot of dry sediment would weigh eighty-five pounds, and on 
this assumption the average per cent, of silt for the period coveted was 
figured at 0.315 of 1 per cent. The smallest value found was about 
one-fourth of 1 per cent., and the largest 1.5 per cent, for a local rain 
of twelve hours’ duration. Major Mills concluded that it would take 
at least one hundred and fifty years to fill the reservoir with sediment. 
The United States Geological Survey carried on these sediment deter- 
minations at El Paso for upwards of one year, as described in Part II 
of the Eleventh Annual Keport. For these determinations it was 
assumed that a cubic foot of the dried sediment would weigh one hun- 
dred pounds. The largest monthly discharge of sediment given was for 
April, 1890, when the amount was 1,671,700 pounds, and the smallest 
was for July, 1889, when the sediment amounted to 39,800 pounds. 
For the year ending July 30, 1890, the total silt, on the assumption 
that a cubic foot would weigh one hundred pounds, is given as sufficient 
to cover a square mile to a depth of 2.75 feet, equivalent to only 1,760 
acre feet. 
While it is possible that a cubic foot of dried sediment may weigh 
eighty-five pounds, or even one hundred pounds, it seems perfectly clear 
to me that this same cubic foot of sediment, if placed in water and 
allowed to absorb what it will, as must occur at the bottom of a reser- 
voir, would swell very much in volume. If we take the three samples 
collected from the Rio Grande at Earlham Bridge, two of which con- 
tained an excessive amount of silt — which, from this very fact, would 
probably be more readily settled into a compact mass — and if we reduce 
