20th.--Traveling for a few hours down the stream this morning, we turned the point of a hill on our left, and came suddenly in sight of another and much larger lake, which, along its eastern shore, was closely bordered by the high black ridge which walled it in by a precipitous face on this side. Throughout this region the face of the country is characterized by these precipices of black volcanic rock, generally enclosing the valleys of streams, and frequently terminating the hills. Often, in the course of our journey, we would be tempted to continue our road up the gentle ascent of a sloping hill, which, at the summit, would terminate abruptly in a black precipice. Spread out over a length of 20 miles, the lake, when we first came in view, presented a handsome sheet of water, and I gave to it the name of Lake Abert, in honor of the chief of the corps to which I belonged. The fresh-water stream we had followed emptied into the lake by a little fall; and I was doubtful for a moment whether to go on, or encamp at this place. The miry ground in the neighborhood of the lake did not allow us to examine the water conveniently, and, being now on the borders of a desert country, we were moving cautiously. It was, however, still early in the day, and I continued on trusting either that the water would be drinkable or that we should find some little spring from the hill-side. We were following an Indian trail which led along the steep rocky precipice--a black ridge along the western shore holding out no prospect whatever. The white efflorescences which lined the shore like a bank of snow, and the disagreeable odor which filled the air as soon as we came near, informed us too plainly that the water belonged to one of those fetid salt lakes which are common in this region. We continued until late in the evening to work along the rocky shore, but, as often afterwards, the dry, inhospitable rock deceived us; and, halting on the lake, we kindled up fires to guide those who were straggling along behind. We tried the water, but it was impossible to drink it, and most of the people to-night lay down without eating; but some of us, who had always a great reluctance to close the day without supper, dug holes along the shore, and obtained water, which, being filtered, was sufficiently palatable to be used, but still retained much of its nauseating taste. There was very little grass for the animals, the shore being lined with a luxuriant growth of chenopodiaceous shrubs, which burned with a quick bright flame, and made our firewood.