It will be the obvious policy of the rebels, in the event of Beauregard's defeat, to send a large column into Texas for the purpose of holding that country for subsistence, where beef and wheat abound. Now, all this can be defeated by strongly occupying Vicksburg and plying a gunboat or two on the Yazoo river. I would also suggest a gunboat to be placed at the mouth of the Red and Arkansas rivers. Whether the impending battle in North Mississippi should occur at Corinth or within the area of a hundred miles, a large part of the enemy's forces will retreat by the Yazoo river and by the railroad to Vicksburg, on the Mississippi, and will then take the railroad through Louisiana into Texas. I handed Honorable Mr. Watson on Monday a letter giving information that the canoes, skiffs, and other transports had been sent up the Yazoo river from Memphis and Vicksburg for the purpose, undoubtedly, of securing the rebels' retreat from our pursuing army. This information I obtained from Mr. Scott, a pilot on the _Memphis_, which conducted the retreat of the soldiers at the battle of Belmont, and had been with the fleet in the same capacity up the Tennessee river. Until June last he resided in New Orleans, and for twenty years or more has been in his present employment. His wife stated this to me, and with a view of obtaining facts about that section of country I requested her to introduce him to me. I was surprised at his general intelligence in regard to the war, and from the facts I derived from him and other practical men I satisfied myself that the Tennessee river was the true strategic point, and submitted a document to this effect to Hon. Thomas A. Scott, dated the 30th of November, 1861, which changed the whole programme of the war in the Southwest, and inured to the glory of our arms in that section and throughout the land. The Government is not aware of the incalculable service rendered by the facts I learned from this pilot, and I therefore take the present occasion to ask his promotion to the surveyorship of New Orleans, for which I should think him well suited in this crisis. I enclose you a letter describing the battle of Pittsburg Landing, which will interest you. Very sincerely, ANNA ELLA CARROLL. * * * * * Extract from the letter to the Secretary of War on the 15th of May, 1862, advising the occupation of Vicksburg: