On the hills and elevated ground the engineer can, comparatively speaking, get along quite comfortably, his principal annoyances being the uneven character of the ground, which compels him to set his instrument very frequently, and the necessity of felling some gigantic tree every now and then. In the valleys and lowlands there is an unceasing round of obstacles. The line may run for some distance over level ground covered with a comparatively open growth, then without warning it encounters the wreck of a fallen tree, and hours are consumed hewing a passage through the mass of broken limbs and shattered trunk, all matted and bound together with vines and shrubbery. A little farther on a stream is crossed, and the line may cross and recross four or five times in the next thousand feet. The engineer must either climb down the steep banks, for the streams burrow deep in the stiff clay of these valleys, ford the stream and climb the opposite bank, or he must fall a tree from bank to bank and cross on its slippery trunk twenty or twenty-five feet above the water. Either on the immediate bank or in its vicinity is almost certain to be encountered a _"saccate"_ clearing. This may be only one or two hundred feet across or it may be a half a mile. In the former case the _"saccate"_ grass will be ten or fifteen feet in height and so matted and interwoven with vines and briars that a tunnel may be cut through it as through a hedge. If the clearing be large, the tough, wiry grass is no higher than a man's head, and a path has to be mowed through it, while the sun beats down into the furnace-like enclosure till the blade of the _machéte_ becomes almost too hot to touch. But worse than anything thus far mentioned are the _Silico_ or black palm swamps. Some of these in the larger valleys and near the coast are miles in extent. Occupied exclusively by the low, thick _Silico_ palms, these swamps are in the wet season absolutely impassable except for monkeys and alligators, and even at the end of the dry season the engineer enters upon one with sinking heart as well as feet, and emerges from it tired and used up in every portion of his anatomy. It is with the utmost difficulty that he finds a practicable place to locate his instrument, generally utilizing the little hummocks formed by the trunks of the clusters of palms, and in moving from point to point he is compelled to wade from knee to shoulder deep in the black mud and water. General reconnaissances from high trees in elevated localities, simple enough in theory, are by no means easy in a country so miserly with its secrets as this, nor are their results reliable without a great expenditure of time, labor, and patience.