It was supposed that there were but two passes through the mountains to the table land; but a third, that of Tula, near Victoria, is now spoken of. This river, appears to penetrate the great barrier between Tampico and Monterey, and takes its rise in the table land, between San Luis, and Zacatecas. It is possible, that the army of Santa Anna may, by this route, keep open a communication with the valley of the Rio Grande, and even send large reinforcements of cavalry and infantry through this pass, so as to threaten our lines on the Rio Grande and Tampico. According to the last accounts, our troops were marching towards Victoria. I should think it all important to take possession of that pass, and close it completely. There are still paragraphs in the papers, speaking of the intended march from Monterey, or Tampico, to San Luis. I think this highly improbable. It will be unsafe for us to move until we are completely masters of the whole country between the river and the mountains, and of all the passes to the table land. It would not do to leave this country in our rear, with all our military depots, but weakly guarded. Of one thing I will speak with confidence; that we shall need all the troops we have on the present scene of operations, and all we shall be able to send for some time. The descent on Vera Cruz, which is said to be in preparation, under the immediate direction of the commander in chief, General Scott, will require, at least, twenty thousand men, and if any considerable proportion be withdrawn from General Taylor, it will leave him in a very perilous situation. What is to prevent Santa Anna from making his head quarters at Victoria? It is said, that cannon cannot be transported by the Tula pass. This may, or may not be. Things deemed impossible have been accomplished by men of bold and enterprising spirit, as he is said to be. Napoleon crossed the Alps in spite of impossibilities, and appeared suddenly in the plains of Lombardy; and I should think the difficulties a hundred times greater than would be encountered by the Mexican Napoleon. I confess, I entertain serious apprehensions for our troops, although of the best materials, and admirably commanded.