The morning of the 20th was fine, with a southerly breeze and a bright sky; and at seven o'clock we were on the march. The country to-day was rather more broken, rising still, and covered everywhere with fragments of silicious limestone, particularly on the summits, where they were small, and thickly strewed as pebbles on the shore of the sea. In these exposed situations grew but few plants; though, whenever the soil was good and protected from the winds, in the creek bottoms and ravines, and on the slopes, they flourished abundantly; among them the _amorpha_, still retaining its characteristic place. We crossed, at 10 A.M. the Big Vermilion, which has a rich bottom of about one mile in breadth, one-third of which is occupied by timber. Making our usual halt at noon, after a day's march of twenty-four miles, we reached the Big Blue, and encamped on the uplands of the western side, near a small creek, where was a fine large spring of very cold water. This is a clear and handsome stream, about one hundred and twenty feet wide, running with a rapid current, through a well-timbered valley. To-day antelope were seen running over the hills, and at evening Carson brought us a fine deer. Longitude of the camp 96° 32' 35", latitude 39° 45' 08". Thermometer at sunset 75°. A pleasant southerly breeze and fine morning had given place to a gale, with indications of bad weather; when, after a march of ten miles, we halted to noon on a small creek, where the water stood in deep pools. In the bank of the creek limestone made its appearance in a stratum about one foot thick. In the afternoon, the people seemed to suffer for want of water. The road led along a high dry ridge; dark lines of timber indicated the heads of streams in the plains below; but there was no water near, and the day was oppressive, with a hot wind, and the thermometer at 90°. Along our route the _amorpha_ has been in very abundant but variable bloom--in some places bending beneath the weight of purple clusters; in others without a flower. It seemed to love best the sunny slopes, with a dark soil and southern exposure. Everywhere the rose is met with, and reminds us of cultivated gardens and civilization. It is scattered over the prairies in small bouquets, and, when glittering in the dews and waving in the pleasant breeze of the early morning, is the most beautiful of the prairie flowers. The _artemisia_, absinthe, or prairie sage, as it is variously called, is increasing in size, and glittering like silver, as the southern breeze turns up its leaves to the sun. All these plants have their insect inhabitants, variously colored--taking generally the hue of the flower on which they live. The _artemisia_ has its small fly accompanying it through every change of elevation and latitude; and wherever I have seen the _asclepias tuberosa_, I have always remarked, too, on the flower a large butterfly, so nearly resembling it in color as to be distinguishable at a little distance only by the motion of its wings. Traveling on, the fresh traces of the Oregon emigrants relieve a little the loneliness of the road; and to-night, after a march of twenty-two miles, we halted on a small creek which had been one of their encampments. As we advanced westward, the soil appears to be getting more sandy; and the surface rock, an erratic deposite of sand and gravel, rests here on a bed of coarse yellow and gray and very friable sandstone. Evening closed over with rain and its usual attendant hordes of mosquitoes, with which we were annoyed for the first time.