From the pass we descended by the north-east to the Otate Brook; crossed a gently rolling plain, with rich pastures, and ascended the Chichihua Mirador, a high hill, from whence the surrounding country could be easily inspected. We took several observations with the barometer, and measured sjveral angles to test Moro's triangulation. We descended to a small valley, crossed the brooks Mentidero and Milagro, and after one and a half miles' travel to the north, we ascended the hills which form the left bank of the Chichihua. Their general direction is to the east; and these hills are highest at the Pericon junction, where there is a cañon about 100 feet wide, with nearly vertical walls, about 150 feet high. A gradual descent to the east brought us to the Chichihua below the Corazo Brook, and where we crosssectioned the Chichihua at a point 71 feet below Chivela; a short distance below, the Chichihua flows into the Corte River. It was here that I conceived it possible to use the Corte as a summit-feeder, because its tortuous course and probable rapids naturally led me to think that it would be easy to overcome the small difference of level without going very far up stream.
Monetza River and Caves. — We left Tarifa December 21, 1870, very early in the morning, under a leaden sky, from which poured a blinding rain. Oar route was by the north-east until we reached Tabla Bolsa, which is a very small valley, lower than Tarifa, since it sheds toward the east. The ranecillo, which we crossed and followed after the last Tarifa Ford, led us to the source of the Monetza. This river flows from under a natural Gothic arch, cut by its waters in the south-west extremity of the Convento Hill. This hill consists of pure black marble, and the walls of the arch or tunnel which traverses it are perforated and jagged, pouring in all directions fine transparent streams of crystalline and delicious water. This natural arch or bridge is 25 feet high, 23 feet broad, and about 120 feet long. A thousand yards below this point, the stream, which flows over a black bed of rocks fantastically water-worn, plunges into a beautiful cave about one half a mile long, and called the Large Convento.
The Monetza was found 112 feet below the summit at its source, and delivering 2.8 cubit feet per second. After this river emerges from the mountain, it is joined by the brook Lena del Monte, and with a uniform grade runs along a fertile valley which terminates in the Chicapa River, at the town of San Miguel, 300 feet below the summit. The material of the Convento Mountain is admirably suited for construction purposes; and a marble and lime quarry can be easily opened at a very convenient distance from the summit-works. I will not describe the exact route from Tarifa to San Miguel, being of little importance to our subject.
The Chicapa was first cross-sectioned at San Miguel, near the Niltepec Ford, though with a result higher than its minimum value, since copious rains had been falling for the past six days.
Six experiments were made for velocity, at the end areas of the portion of the river chosen, using the surface velocity reduced to mean velocity by Weisbach's formula. This same method was employed in all important rivers. The village of San Miguel is on the right bank of the Chicapa, and at the point of confluence of this river with the Monetza and Xoxocuta rivers, being shut in by high mountains on all sides.
