These so-called bancos were formed by a combination of "slow and gradual erosion" coupled with "avulsion" in the following manner: Where the river passes through low alluvial bottoms with banks of fragile consistency and slight fall the channel continually changes from right to left, eroding the concave bank and depositing on the convex. This occurs in low as well as high water, though the changes are more marked during high water stages. These erosions are greatest where the water in a tangent from a curve strikes the bank at an acute angle, ceasing when the angle becomes so obtuse that the water is readily deflected by the consistency of the bank. When the curve forms a circle the radius of which is dependent on the consistency of the earth and the volume and velocity of the water, erosions practically cease and the river turns upon itself in a circle and forms a "cut-off," leaving the land thus separated (called a banco) somewhat in the form of a pear or gourd, with the stem cut by the river's current at the moment of separation. (See cut of the double Banco de Santa Margarita. Proceedings Boundary Commission, Vol. I, p. 191.) In many cases through ensuing changes in the channel an American or Mexican banco would be entirely cut off even from the river and wholly surrounded by land within the jurisdiction of the other country. The origin of these bancos was so different from our expectations that both the Mexican Commissioner and I, after deliberate consideration, concluded that their process of formation, their form and constantly changing character, could not have been contemplated by the conventions creating the treaties of 1884 and 1889. We both suggested to our governments the reconsideration of Articles I and II of the treaty of 1884, as far as they related to these bancos, to the end that provision might be made for transferring all such bancos to the sovereignty of the United States or Mexico according as they lay on the American or Mexican side of the present river channel, without disturbing the private ownership as it might be ascertained. This treaty was negotiated and ratified in 1905 and has since then worked to the satisfaction of both governments and resulted in the "elimination" of perhaps 75 of these bancos and the maintenance of the international boundary line in the center of the running river. Some of the difficulties under which the Commission did much of its work on the lower Rio Grande will appear from the following incident which occurred while the Commission was considering the case of the Banco de Granjeno, near Havana.