Note 702 — Chapter XI · —The Anthropo-Geography Of Rivers

Poor as a scientific boundary, a river is not satisfactory even as a line of demarcation, because of its tendency to shift its bed in every level stretch of its course. A political boundary that follows a river, therefore, is often doomed to frequent surveys. The plantations on the meanders of the lower Mississippi are connected now with one, now with the other of the contiguous states, as the great stream straightens its course after the almost annual overflow.702 The Rio Grande has proved a troublesome and expensive boundary between the United States and Mexico. Almost every rise sees it cutting a new channel for itself, now through Texas, now through Mexican territory, occasioning endless controversies as to the ownership of the detached land, and demanding fresh surveys. Recent changes in the lower course of the Helmund between Nasralabad and the Sistan Swamp, which was adopted in 1872 as the boundary between Afghanistan and Persia, have necessitated a new demarcation of the frontier; and on this task a commission is at present engaged.703 In a like manner Strabo tells us that the River Achelous, forming the boundary between ancient Acarnania and Aetolia in western Hellas, by overflowing its delta region, constantly obliterated the boundaries agreed upon by the two neighbors, and thereby gave rise to disputes that were only settled by force of arms.704