NEW ORLEANS, February 22, 1865.

Lieutenant General U. S. GRANT,

Commanding Armies of the United States, City Point, Va.:

GENERAL: After unavoidable delays, such as failures of connections, I at last reached this city, and now wait only for a vessel to carry me to Brazos. Arrived there it will take but few days to obtain all the facts necessary for a report on the relations, military and commercial, of Matamoras and Brownsville. From reliable information already at hand, I am justified in saying now that the statements of Mr. S. S. Brown, forwarded you from Baltimore, are in no wise exaggerated. Matamoras is to all intents and purposes a rebel port, free at that, and you can readily imagine the uses they put it to. There is never a day that there are not from 75 to 150 vessels off Bagdad, discharging and receiving cargoes. I would have postponed writing to you, however, had it not been for a report in official circles to the effect that our consul at Matamoras has been ordered off by Mejia. That personage (the consul)will doubtless communicate the particulars to Mr. Seward, and I therefore refrain from sending a version of the affair, but venture to suggest that it might be well enough not to notice it until I can be heard from. In an unauthorized way I will endeavor to possess myself of the facts. Should they turn out serious, I am sure you will discern the policy of waiting until it can be seen whether the Mexican Republic cannot be put in position to fight its own and our battles without involving us, an eventuality exactly coincident with Mr. Seward's views. As to the prospects of such an eventuality, without going into details, I will say generally, but positively, that I have now an arrangement so complete that it will hardly be necessary for the Government to loan me a gun, not even a pistol. This arrangements depends entirely upon your giving me command of Texas as a military department, with orders to report directly to yourself, and upon your sending me a division of infantry and a brigade of cavalry, with the ordinary complement of guns. The main body of these forces acting on the defensive and posted at San Patricio, the lowest ford on the Nueces River, will completely sever communication between the Rio Grande and Middle and Eastern Texas. You served, if I am not mistaken, on the Rio Grande line, but I am not sure that you have a present recollection of the topography of the Nueces region. I will therefore venture to speak with some particularity of San Patricio. It is about twenty miles northwest of Corpus Christi. The road connecting the two points is on the right bank of the river and always good. The west bank of the river is very bluffy. The channel is deep, but narrow. The east bank is low and level and can be overlooked from the opposite bluffs fifteen or twenty miles. At San Patricio is a ford which is, so to speak, a great funnel through which everything going and coming from Matamoras, Rio Grande City (near Camargo), and Laredo (old Fort McIntosh) must pass; and of necessity, for the desert belt, called Mustang Prairie, makes the region between the Rio Grande and the Nueces ordinarily impassable for travel except by way of the few traces marked by springs. Of these traces there are but three at all useful to the rebels, because they are the only ones that strike the Rio Grande in a southwesterly direction. One beginning at Laredo, another at Ringgold City, and the third at Brownsville, all of which unite about twenty-five miles from and west of San Patricio Ford. This rough description will enable you to see that if your object is simply to sever connection or communication between Mexico and Texas, it is only necessary to fortify San Patricio. This done, small garrisons can safely hold Brownsville, Rio Grande