Darien is a province of the State of Panama and its boundaries as given by Lieut. Sullivan in his comprehensive work on "Problem of Interoceanic Communication," are as follows: "The Atlantic coast line is included between Point San Blas and Cape Tiburon; that of the Pacific extends from the mouth of the Bayano to Point Ardita. The eastern boundary is determined by the main Cordillera in its sweep across the Isthmus from a position of close proximity to the Pacific, near Point Ardita, to a similar position near Tiburon, on the Atlantic. The valleys of the Mandinga and Mamoni-Bayano determine its western limit."
The Darien hills as seen from the Atlantic side present to the view an apparently solid ridge of mountains, although there are in reality many low passes which are concealed by projecting spurs.
The dividing ridge hugs close to the Atlantic, and the rivers, of which there are a great many on this side, plunge abruptly to the sea. On the Pacific side the rivers have a much longer distance to flow before reaching the sea, and the territory bordering on the ocean is low and swampy. The tidal limit of the Tuyra River is nearly fifty miles from its mouth, and on this river and many of its tributaries one can travel many miles inland before ground sufficiently solid to land upon can be found. The vegetation within this low lying area is thick and closely matted together, and this fact taken in connection with the swampy character of the ground, makes travel on foot through any portion of it exceedingly difficult. Therefore the various rivers, which form a very complex system and penetrate everywhere are the natural highways of the country. The chief rivers on the Pacific side are the Tuyra and Boyano with their numerous tributaries and on the Atlantic watershed is the Atrato.
A peculiarity noticed at Real de St. Marie, which is at the junction of the Pyrrhi and Tuyra rivers and at which point the tide has a rise and fall of twelve or fifteen feet, was that at low tide it was impossible to enter the mouth of the Pyrrhi with a boat, while five or six miles up the stream there was always a good supply of flowing water and at double that distance it became a mountain torrent.