The first two points within the limits above mentioned, where communications are most practicable, are the following:--_First_, in the territory of Mexico, from the mouth of the river Guazacoalcos, on the Gulf of Mexico, to the mouth of the Chimalapa, in the Gulf of Tehuantepec, on the Pacific, between the parallels of 16-1/2 deg. to 18-1/2 deg. N. lat. The distance from sea to sea at this part is 92 geographical miles, in a south-west direction. The sources of the streams which flow, the one eastward into the Gulf of Mexico, and the other westward, into the Pacific, come within the short distance of 20 miles of each other. _Secondly_, The channel from the Gulf of Dolce, which communicates with the Gulf of Mexico, to the southward of Honduras or the Balize, to Trinidad, situate on a bay in the Pacific, to the north of Point Remedios. The distance of the Gulf of Dolce to the Pacific, at the point just mentioned, is 60 geographical miles, with the advantages of the courses of rivers which bend their courses to the opposite oceans. But if it is correct that the River Balize is, as it has been stated to be, navigable upwards in its course to a distance of 200 miles, then it must penetrate so deeply into the continent, that its sources must approach to points still nearer to the Pacific than the Gulf of Dolce, or its tributary streams. It is doubtful, however, if any canals could be cut in either of the lines mentioned, because the land rises very considerably, forming in the central parts what is denominated Table Land, and is in general studded with ridges and high volcanic mountains, while the ports on either shore are neither very commodious nor of safe approach. There has been of late years also a tolerable good road constructed in the first-mentioned line, which will tend greatly to facilitate the communication from sea to sea, so far as the interests of Mexico are immediately concerned. These points adverted to are the only probable channels of (p. 087) communication to the northward of the River St. Juan and Lake Nicaragua, which, like the last-noticed line, are situated in the territory of the Republic of central America, the capital of which is San Salvador. For reasons which will subsequently be adduced, the consideration of this important position is left until those points in the Isthmus of Panama and Darien have been particularly noticed and examined.