The wild guanacoes, and the deer, and the ostriches ranged in thousands over the pastures of their native regions, and, with hares, partridges, and armadilloes, afforded abundant sport to those sent out to shoot them. For some days the army was almost entirely subsisted upon them. Vast quantities of armadilloes, especially, were caught by the soldiers. One memorable afternoon's chase is recorded, in which upwards of 400 were taken; and a more delicate dish than one of these little animals, roasted, in his own shell, I will venture, from my own experience, to say, is not to be had in any part of the world. The rivers and lakes swarmed with wild and water-fowl of every sort, named and nameless, from the snipe to the beautiful black-necked swan peculiar to that part of the world.[43] An observation was taken on the Chapeleofú in latitude 37° 17´ 34"; shortly after which the army left its course, and marched eastward to the Tandil, where they encamped, and whence the surveying officers reconnoitred the surrounding country, and determined upon the site for the new fortification. The position of the fort constructed there has been fixed by repeated observations in latitude 37° 21´ 43"; longitude, west of Buenos Ayres, 39´ 4"; variation 15° east. It stands upon a small eminence, one of a lower group of hills which skirts the more elevated range beyond, and from which it is divided by the bed of a streamlet, which, after passing the works, about a quarter of a league to the eastward, and being joined by another from the westward, forms the river Tandil, which runs north till lost in the marshes in that direction already spoken of. It is screened to the west and north-west by a range of hills rising 300 or 400 feet above it, the summits of which are strewed with large masses of quartzose rock, having a very remarkable appearance when seen from a distance. The highest part of the range of the Tandil, about two leagues to the south-east of the fort, was ascertained to be about 1000 feet above the level of a small stream which runs along its base. It is visible from a distance of forty miles. The height of this part of the range gradually falls off till lost in a wide plain or vale, about twelve miles eastward of the fortification. The climate in winter was found to be very cold; the prevailing winds from the south and south-west.[44] In the month of April the thermometer was twice 1-1/2° below freezing-point; but variations of 20° and even 30° in the course of the day were of common occurrence. In that month (April) the highest of the thermometer was 68°, the lowest 28-1/2°; in May the highest was 61°, the lowest 31°; in June the highest was 72°, the lowest 39°; in July the highest was 79°, the lowest 41°. In the summer the heat was almost insufferable, particularly in the low lands; but in the spring and autumn, which are the best seasons, the weather was found temperate and very agreeable.