5th. The Rio de Tampico, is formed by the union of the rivers Panuco and Tula. The upper source of the Panuco is in the neighborhood of the city of San Luis Potosi, the capital of the state of that name. Near half a league north north-east of this city, in the valley de la Pila, rises a spring which is protected by a basin of fine masonry, and conveyed by an aqueduct to town. Several other streams, coming from the south-west, unite with this source and form the Panuco. West of the first of these streams, swells up the mountainous ridge which divides the waters of Mexico between the Pacific and the Atlantic. The Panuco courses eastwardly,—and, passing rapidly through the Laguna Chairél, unites with the Tula. This latter stream mingles the waters of the rivulets Tepexi, Tequisquiac, and Tlantla, in the northern part of the state of Mexico; and receiving, by the canal of Huehuetoca, the water of the Rio Quautitlan, it winds onward through the valley of Tula, and near the limits of the states of Queretaro and Vera Cruz, until it joins the Panuco. These united rivers receive in the state of Tamaulipas, the name of the Rio de Tampico, which debouches, finally, in the Gulf of Mexico.
6th. The Rio Blanco rises in the state of Vera Cruz, near Aculzingo, at the foot of Citlaltepetl, or the mountain of Orizaba. It courses onward through a varying and rough channel among the mountains and plains, until it is lost in the lagunes near Alvarado.
7th. The Rio de San Juan. The sources of this river lie partly in the metallic mountains of Ixtlan, in the state of Oajaca, and partly in the neighborhood of Tehuacan de las Granadas. Many large, but wild streams, spring up in these mountain regions, and form the broad but shallow Rio Grande de Quiotepec. This river, after winding through the valley of Cuicatlan, receives, from the south, the large stream of Las Vueltas; and all these unite to form the Rio de San Juan, which pursues its eastern course until it approaches the coast near Alvarado, when it divides into two arms. One of these, named Tecomate, joining the Cosomaloapan and Paso, form the large lagunes of Tequiapa and Embarcadéro,—whilst the other arm, by a different course, also debouches in the same lagunes.
8th. The Rio de Guasacualco, rises at about 16° 58´ of north latitude, and 96° 19´ west longitude, from Paris, in the mountains of Tarifa, and pours onward towards the east, receiving accessions from a great number of small mountain streams and rivulets, until it falls into the Gulf of Mexico.
9th. The Rio de Tabasco, or Rio de Grijalva, or Rio Guichula, rises in the mountains of Cuchumatlanes towards the centre of Guatemala, and falls into the gulf at the port of Tabasco.
10th. The Rio de Usumasinta, rises also in Guatemala, and debouches in the Laguna de Terminos.
II. Small Eastern Coast Streams.
Many of these streams are, in fact, not entitled to the name of rivers, though a few of them are important, whilst all are valuable to some extent for agriculture, transportation, irrigation, or occasional water power.