[Illustration: LYNCH'S LEVELLING PARTY.] "Lieutenant Lynch," said the Doctor, "landed at the Bay of Acre in March, 1848, carried his boats on trucks drawn by camels over the mountains of Lebanon, and launched them in the Lake of Gennesaret. From this lake the party descended the Jordan to the Dead Sea, spent three weeks in a survey of that body of water, and then 'levelled' the route to the Mediterranean, in order to settle the question of the relative heights. They found that no fish or living thing belongs to the water of the Dead Sea, and all fish from the Mediterranean or the ocean die very soon after being placed in it. Ducks swim in the water without injury, but it is fatal to them to be plunged beneath it. As it contains nothing for them to eat, they have no inducement to dive. [Illustration: 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?" CHAPTER XXVI. FROM THE DEAD SEA TO THE JORDAN, JERICHO, AND JERUSALEM.--THE VALLEY OF THE JORDAN. [Illustration: REEDS AND RUSHES ON THE JORDAN.] It was a ride of less than two hours from the Dead Sea to the Jordan; the ground was level and the horses in good spirits, so that the whole party indulged in the luxury of a gallop. The course of the Jordan was indicated by trees and great masses of reeds, but the stream was so completely concealed by them that its waters were not revealed until rein was drawn at the bathing-place of the pilgrims. The boys could hardly restrain their impatience to reach the waters of the river that is so intimately connected with the history of Christianity. Of course they made immediate preparations for a bath, according to the custom of the great majority of visitors; the water was so cold that they remained in it only a few minutes, and were glad to resume their clothing and make a calm study of the scene.