the right of our road, or east, at the distance of from three to five miles, a steep and high mountain chain of limestone rises; and another chain to our left, distant from 10 to 15 miles. Both chains gradually diverge, but especially the eastern, which seems to run towards the northeast, and to return thence towards the southwest, at an angle, leaving a large cul de sac, or pouch, in the middle, from which form the country has probably received its name, as Bolson means pouch, or pocket. The barometrical profile will elucidate, better than a description, this pouch-like slope of the country, which extends most likely as far towards the north as the Rio Grande. Passing over a ridge, on our road, I enjoyed the most distant view over the Bolson de Mapimi, at the southern base of which we are at present travelling. All around us was an immense chaparrál plain, and in the distance of from 15 to 20 miles ahead of us the Rio Nasas, which runs towards the north, into the above mentioned pouch, and forms there the large Laguna de Tlagualila, (on maps generally called lake Cayman.) Neither the lake nor the northern end of the Bolson was to be seen from the place of my observation; but the outlines of the surrounding mountains, disappearing in the most distant horizon, seemed to extend towards the north to about 80 miles in length, and towards east and west to an average breadth of 30 miles. The limits of the Bolson have never been clearly defined, either in geographical or political regard. The northern part of it belongs to the State of Chihuahua; the southern, to that of Durango; but no certain boundary line seems to exist. As to the physical properties of the Bolson, the general impression is, that it represents a low, flat, swampy country, and a mere desert, which is but partly true. The two terminating points of our march through the Bolson are Mapimi, where we entered it, and el Pozo, or rather a point between Pozo and Parras, where we left it. At Mapimi, the elevation above the sea was 4,487 feet; in the valley of the Nasas, at San Sebastian, 3,785; at San Lorengo, 3,815; at San Juan, 3,775; and towards the eastern edge of the Bolson, I found el Pozo 3,990, and Parras 4,987 feet above the sea. We perceive, therefore, that the valley of the Nasas river, which may be called the vein and centre of the Bolson, has a mean elevation of 3,800 feet; and though from 500 to 1,000 feet lower than the surrounding country, it occupies nevertheless a considerable absolute elevation above the sea. The soil in the Bolson is less sandy and better than in the higher country; in the valley of the Nasas, especially, is a black rich soil, and most luxuriant vegetation, as we shall see hereafter.
From the ridge, from whence I overlooked the valley, the road descends slightly about five miles to a hacienda, where formerly silver ores used to be smelted. They have a large and deep well here, from which the water is drawn by a mule, and in peaceable times sold to the thirsty traveller: we of course refreshed ourselves, gratis. Some miles further, two more ranchos lie on the road, where, also, wells have been sunk. Although the soil looks everywhere dry, and the nearest water-course is the distant Nasas, good water is got everywhere in this valley by digging to a certain depth. Near these ranchos the road forks, and a more northern or southern route can be taken from here. The northern route leads by Alamito, San Lorenzo, and San Juan, (all settlements on the Nasas,) to el Pozo; while the southern goes to San Sebastian, (on the Nasas,) and by Matamoros and Laguna de Parras, to el Pozo. The latter route is considered the shortest; we selected it, therefore, and marched on the right hand road as
