Iceland is well watered, having many streams, all of which are rapid, for the greater part flowing over beds of lava and quicksand. In some of the wider fords stakes have been set so that the traveller may not get lost in crossing them on horseback during a dense fog. In the summer the frequent rains make travelling very unpleasant unless one is suitably equipped with water-proof garments. In the Hvita, or White River, is the celebrated Gullfoss--literally, "goldfall"--a fall that rivals Niagara in the height of its two cataracts. A few garden vegetables excepted, little or no agriculture is attempted; the chief dependence of the people is the rearing of sheep, cattle, and horses, fishing, and the collecting of eider-down. The streams are filled with excellent fish, including the salmon; off the coast are codfishing grounds equal to, if not surpassing, those of Newfoundland. The most valuable mineral is sulphur, the supply of which appears to be inexhaustible. The chief exports are wool, oil, fish, horses, eider-down, knit goods, sulphur, and Iceland moss. Transparent calcite, a mineral commonly called "Iceland spar," is found, one mine of which furnishes an excellent quality. It is highly prized by mineralogists on account of its double refractive qualities. If a piece of this mineral be placed over a word, the letters forming it will appear double. Iceland spar is used chiefly in the optical instrument known as the polariscope. Eider-down consists of the soft, fine feathers growing on the breast of the eider-duck, great numbers of which frequent the coast and lakes of Iceland. This duck is wild except at the nesting season; then it is as tame as the domestic fowl and makes its nest not only around and on top of the buildings but frequently inside them. A heavy fine is imposed on any one killing a duck at this season. When about to lay, the duck carefully lines her nest with down plucked from her breast. Then people remove it from the nest and the duck pulls more down from her breast to replace that taken. This process is repeated several times. When the duck has stripped her own breast the drake comes to the rescue and furnishes down from his. A certain number of the eggs are also taken. These, though inferior to those of the swan, are esteemed a great delicacy. Swans also are killed on many of the lakes. Iceland is the resort of the fishing fleets of several nations; the value of the annual catch averages about ten million dollars. Much of the catch consists of food fish, but many are caught for the oil. The only trees found growing on the island are birch and ash, and they seldom exceed ten feet in height. A few juniper bushes and willows are found here and there.