148 MEXICO, CENTRAL AMERICA, WEST INDIES. 



sparsely peopled region, also receives its first contributions fiom the "altos," 

 or uplands, of Guatemala. According to Bras eur de Bourbourg, the E,io Blanco, 

 the main headstream, soon after the Rio Negro confluence trends at first eastwards 

 in the direction of Honduras Bay. But after changing its name ten times accord- 

 ing to the tribes settled on its banks, the Rio Chixoy or Lacandon, as it is here 

 usually called, turns north and north-west to its confluence beyond the uplands 

 with the Rio de la Pasion, a yellowish stream from the border ranges south of 

 British Honduras. It mostly flows sluggishly between its Avooded banks, but 

 during the rainy season it floods its banks and at times rises 50 feet above low- 

 water level. Below the confluence the united stream takes the name of 

 TJsumacinta, under which it is indicated in the diplomatic conventions, according 

 to which it has been chosen for a space of nearly 70 miles as the common frontier 

 of Mexico and Guatemala. Navigable bj' canoes throughout a great part of its 

 upp3r course, the Usumacinta pierces the last range of hills by a series of gorges 

 and rapids which obstruct all navigation by large craft. This section, where the 

 stream is contracted between vertical walls, takes the name of Boca del Cerro, or 

 "Mouth of the Mountain." The people employed in felling mahogany and cedar 

 in this district mark the blocks and throw them into the current, by which they 

 are carried from rapid to rapid down to Tenosique. Here the stream resumes its 

 placid course, and is soon joined by the Rio San Pedro from Lake Peten in 

 Guatemala. The waters of this affluent are so thoroughly saturated with carbonate 

 of lime that the snags arrested by the reefs ate rapidly petrified and thus form 

 bars athwart the stream. 



Beyond the confluence the TJsumacinta follows a winding course through the 

 flat plains, till the first branches of the delta begin to ramify from the main stream 

 some 60 miles above the Gulf. Some of these branches trend north-eastwards 

 towards the Terminos lagoon, some flow straight to the sea, while others intermingle 

 their waters with branches from the Grijalva and from the secondary affluents of 

 the twin river. Including the channels discharging into the Terminos lagoon, 

 the face of the delta has a development of about 125 miles, while all the ramifica- 

 tions occupy a sj)ace that may be estimated at 6,000 square miles. Scarcely any 

 other fluvial basin of like size has created such an extensive accumulation of sedi- 

 mentary matter in the waters of a marine inlet. 



The Barra de Tabasco, or principal channel, lies about the middle of the delta 

 region, and has a depth of from seven to ten feet according to the seasons. This 

 channel is deepest during the prevalence of the north winds, especially in the dry 

 season. During the floods, when the sea is covered with a yellowdsh water for a 

 distance of 35 miles from the coast, the bar is considerably' raised by tiie sediment 

 brought down with the flood waters, so that at such times vessels drawing no more 

 than six or seven feet will not always venture to force the obstruction. The San 

 Pedro, another branch of the delta lying farther east, although shallower, is more 

 constant. The deepest, but also one of the most shifting, passages is that of Chil- 

 tepec in the east, where the sounding-line occasionally reveals a depth of thirteen 

 feet. Here is discharged the Rio Seco, or " Dry River," which is supposed to have 



