By guarding this line, the valley can be cut off from all supplies from Mexico; with the exception of a small quantity of indian corn, and the herds of the ranchos, very little can be procured in it for the support of an army. Our own safety requires, that we should take possession of all the principal towns as soon as possible, and garrison them with a sufficient force. It will, also, be necessary to establish civil authority, for the country thus cut off from the central Government. Its head must necessarily be military, as also the local superior authorities, although using the machinery of Alcaldes &c., for the purpose of carrying it on. The political Government, must be suspended, as the consequence of being cut off from both the State and federal authorities of Mexico. It would now seem to be the general impression, that nothing effectual can be done to bring Mexico to terms without taking Vera Cruz, and marching to the capital; and this appears to be the opinion of General Taylor at least, that if the march be resolved upon, then Vera Cruz, is the proper point to start from and not from Saltillo. A short time will determine. We have, thus far, been operating at vast expense, with an army of fifteen thousand men, about one half regulars, and the other half, volunteers, on the remote, thinly inhabited, northern frontier of Mexico; and we talk of marching through a densely peopled country with numerous defiles! If there be any thing like the resistance made by us during the revolutionary war, thirty thousand men, at least, will be required for the march from Vera Cruz to Mexico. A part of the force under General Taylor may now be spared, but not so as to weaken and disable him from repelling a part of the army of Santa Anna, if he should think proper to detach it, for the purpose of attacking Saltillo. It would be presumptuous in me to venture an opinion on military movements; but considering the formidable army now organized by Santa Anna, and the uncertainty as to the point which he means to attack, I should think, that it would not be safe to draw off any very considerable portion of General Taylor’s force from the defence of the lines they at present occupy.