234 THE AMERICAN MONTHLY [December, 
they may be seen partly filled with the déé7zs of the crushed salt, which proves that 
they are actually cavities and not illusory. 
It having been proved that the salt contains only traces of water, it may be inferred 
that the cavities are filled with a gas or with atmospheric air. Otherwise it would be 
difficult to account for the explosion when heated. 
On examining the salt after heating, it was found that the transparency was not 
materially impaired except at those points where the box-like cavities were shattered 
by the escaping air under pressure. They had lost their beautiful form and had 
become irregular, roughly globular cavities, filled with broken fragments of salt. In 
every direction from the shattered cavities the substance was fissured and fractured, 
showing the great force exerted by the escaping gas or air. It is a mystery how these 
beautiful cavities could be formed in so hard and anhydrous a substance as rock salt. 
After actual food and water, salt is one of the most necessary requirements of man 
and animals, and it is a question if a healthy bodily condition could be long main- 
tained without it. Salt is also largely employed in manufactures and the arts. 
Rock salt is not always so pure as the specimens shown you this evening. In Eng- 
land it is colored red by the oxide of iron it contains. It is also sometimes contami- 
nated by clay and sand, and often by imbedded associate minerals, as gypsum, 
anhydrite, borax, glauberite and others; still it is seldom, if ever, so impure as’ salt 
made from sea-water, for which reason it commandsa higher price. It dissolves more 
slowly than the more impure varieties, which property fits it for certain purposes and 
uses in the arts. Pure salt does not deliquesce except in a very moist atmosphere. 
Salt obtained artificially contains various impurities which impair its value. These 
impurities are generally magnesia, gypsum, bromine and iodine, with much organic 
matter, while rock salt is free from them. This has led to the theory that seawater 
takes its salt from beds of rock salt, instead of rock salt being deposited from the 
ocean. This theory is strengthened by the fact that rock salt is sometimes absolutely 
anhydrous. 
While inferior salt may be extracted from brines found in nearly all countries, rock 
salt is rather rare. It occurs in very large deposits in England, Poland, Hungary and 
Germany. In the high mountains of Chili it is met with at an elevation of 9,000 feet 
above the sea level. In Spain, 16 leagues from Barcelona, there is a mountain of 
salt three miles in circumference and 500 feet high. It is quite pure. No gypsum 
is found with it. This mineral has been found also in considerable quantities in New 
South Wales. 
It has long been known that rock salt existed in very large quantities in Nevada and 
Arizona. On Holt’s map of California and Nevada, published in 1876, a depositin Lincoln 
county, Nevada, is described as being five miles long and 600 feet high. This locality 
lies 53 miles, by the scale of the map, a little west or north from Callville, on the great 
bend of the Colorado river. Some years ago I examined specimens and found them 
to be very pure. 
In Cleveland's ‘Mineralogy,’ published in 1816, I find a statement that ‘rock salt 
is found in Californiain very solid masses.’ The writer probably referred to the pen- 
insula of Lower California. 
In the sink of the Colorado desert in San Diego county, deposits of salt have been 
discovered, and are rather extensively worked, but this salt is probably the result of 
the evaporation of the waters of an ancientinland sea, cut off from the great ocean by 
the delta of the Colorado river, or by an upheaval of land, gradual or otherwise. The 
water, under the influence of the sun and the dry climate of the locality, became less 
until a resulting small lake of concentrated sea-water finally dried and left the deposit 
of salt. Thisis a good theory until a more thorough study of the deposit is made. It 
is now covered by silt and déév7’s washed down over it during many winters of rain- 
storm and cloud-burst. 
The associate minerals often found with rock salt have also great value. Chloride 
of potassium in very large quantities is extracted from beds overlying the salt de- 
posits at Stassfurt, in Saxony. Some idea of the quantity may be inferred when the 
statement is made that in 1863-64, 400 tons of carnadlite were raised. The yield in- 
creased annually until 1875, when the production was 494,414 tons. Carnadlite 
contains theoretically 26.88 per cent of chloride of potassium. 
If a deposit of this character should be discovered in connection with one of our great 
salt deposits, its importance to California and the Pacific coast can scarcely be 
estimated. 
Mr. Hanks illustrated his essay with specimens which were examined under the 
