MEMORANDUM.

Brigadier-General Baylor arrived in San Antonio from Richmond some time in August, bringing full authority to raise a force of 6,000 men, and with instructions to retake and hold New Mexico at all hazards. The expedition is organizing in San Antonio now. C. H. Merritt, of El Paso, is quartermaster to the expedition; Judge Crosby, also of El Paso, is assistant adjutant-general.

An agent is now (September 8) in Matamoras purchasing the necessary transportation and supplies. The purchases are made with French drafts raised on some cotton sent into Mexico. This information comes from two sources (from San Antonio and Matamoras) by two different letters, which agree in every particular. Nothing is said in either as to the time of starting or the route to be taken by the troops. Both letters are from reliable men, and the information can be depended upon in every particular. One letter mentions the fact that Judge Hart's train has been purchased for this very expedition. The letters bear the date of September 7 and 10 respectively. One letter is from Gabriel Valdez to his brother in El Paso; the other from C. H. Merritt to Mr. Fellman, of Chihuahua.

HEADQUARTERS DEPARTMENT OF NEW MEXICO, Santa Fe, N. Mex., November 18, 1862.

Col. JOSEPH R. WEST,

Commanding District of Arizona, Mesilla:

COLONEL: I have the honor to acknowledge the receipt by special express of your letter of the 13th instant in relation to a report in circulation in Chihuahua and El Paso, Mex., that General Baylor, C. S. Army, has for some time been preparing to invade New Mexico from Texas with 6,000 men. The report is sufficiently circumstantial for us to consider well what we should do in the way of timely preparation for such an invasion. This country is so extended and so open to attack along its eastern frontier and has so many avenues of approach from the rebel States of Arkansas and Texas, either of which avenues an enemy can choose and cover his real designs by diversions upon the others, and, besides, our force all told is so small in comparison with the reported strength of the enemy, that to mature a perfect plan to repel the threatened attack will call for no little reflection upon all the elements here which must enter into the calculation before we can arrive at definite conclusions upon the subject. What you are to do in case any part of the enemy's force comes into the country by the route pursued by General Sibley in his late incursion seems to be quite plain. The force coming by that route will have a march of over 600 miles before it can enter the valley of the Rio Grande, and for this distance will have to transport all the subsistence stores which it will consume. He who commands this force must count on replenishing his magazines after his arrival. Therefore so far as your command is concerned and what you are now to do seems a problem easy of solution. At all events the following are the essential points on which you will promptly act, preliminary to what you will be required to do as time may develop the matter still further:

You will at once secure all the corn and grain which you can possibly buy from the people at San Elizario, Socorro, Isleta, Franklin,