This range of hills ends at the Tamborcito bend of the San Juan, four miles below the mouth of the San Francisco, and is the last easterly projecting spur from the mountain backbone of the interior. Between it and the coast there are, however, mountain masses of equal or greater elevation, notably "El Gigante" and the Silico hills, the former some fifteen hundred feet high, but these are simply isolated mountain ganglia, their innumerable radiating spurs speedily giving way to swamps or river valleys.
The streams that flow down the eastern slope of the Silico hills are, from their sources to the lowlands, of almost idyllic beauty. Beginning as noisy little brooks tumbling over black rocks in a V-shaped ravine near the summit of the hills, they rapidly gather volume and slide along in a polished channel of trap, tumbling every now and then as sheets of white spray over vertical ledges forming here and there deep green pools, and then after they have passed down among the foot-hills, rippling in broad shallow reaches over sunlit beds of bright yellow gravel. The water of these streams is clear and sparkling as that of an Alpine stream and apparently almost as cool. The insect pests of the tropics are unknown in the elevated portions of their valleys, and I have slept more than once beside one of these streams, several hundred feet above sea level, without a mosquito bar, while the delightful "trades," rustling through the trees above me, brought the murmur of the Caribbean surf miles away, to mingle with that of the stream.
The soil of this range consists, to a depth of ten to forty feet, of clay of various grades and colors, red prevailing. In the valleys this clay is almost invariably of a very dense consistency, and deep, dark red in color.
From the foot-hills of the range to the coast, is a low level stretch of country, a dozen miles wide, interspersed with lagoons and swamps. Near the hills, where the elevation of the ground will average about fifteen feet above sea level, the soil is composed almost entirely of the before mentioned red clay, which occasionally assumes the form of hummocks. Within about six miles of the coast this stratum of clay gradually disappears under a layer of sand, which is in turn covered, by a vegetable mould, to a depth of a few feet. From this point to the sea the average elevation is barely five feet above the sea level, and the sand and mould above mentioned are the only materials met. A short distance from the ocean the vegetable earth-covering disappears and only the sand is left, extending to an unknown depth and reaching out into the sea.