THE CAVERN OF USDUM.
"At the southern end of the Dead Sea is the Mountain of Usdum, which contains a cavern three or four hundred feet deep, in which there are deposits of salt. There are other salt deposits in the neighborhood, and it is believed that the Dead Sea derives its saltness from the dissolving of these deposits, and also from the substances brought down by the River Jordan."
"Every lake without any outlet is salt, is it not?" Fred asked.
"Certainly," replied the Doctor; "it is a rule of nature that has no exception. All water from springs, brooks, and rivers contains salt gathered from the earth, and sometimes the quantity is considerable. It is the slight amount of salt that makes water palatable; if you taste of pure distilled water you will find it 'flat,' and its purity is what makes it so.
"The salt brought down from the land gradually accumulates; the water passes off by evaporation, but the salt remains. As time goes on the saltness of the water increases, so the scientific men tell us, and perhaps millions of years hence the ocean may be as strongly impregnated as the Dead Sea. Who can tell?"