CAMP NEAR SAN ANTONIO, TEX., May 12, 1861.

Colonel L. THOMAS, Adjutant-General U. S. Army.

SIR: In connection with the report which I have this day forwarded, relating to the surrender of the battalion of the Eighth Infantry under my command to the forces of the Confederate States of America, near this place, I also present the following details of the latter part of the march and the circumstances which determined that surrender.

This report was not transmitted with the other, as it is extremely uncertain whether any reports of an official character are permitted to pass through the post office here, or those elsewhere in the South.

On leaving Fort Bliss sufficient transportation could be procured to carry subsistence for only forty days, in which time it was expected the command would reach San Antonio, making some little allowance for detentions by the way.

At Forts Quitman and Davis stores were taken to last the commands from those posts to San Antonio, not being able to carry more with the transportation at hand. From Camp Hudson to Fort Clark persons were occasionally seen on the road who appeared to be watching our movements, but they said they belonged to rangers who had been on a scout.

At Fort Clark, where I arrived on the 2nd of May, I learned that the mails had been detained for several days to prevent me from receiving information. It was reported by a stage passenger that the officers at San Antonio had been made prisoners of war. On all these subjects there were contradictory reports, and no information could be obtained which would warrant any hostile act on my part. Such supplies as were called for were readily furnished, and offers of services were proffered by the commanding officer. This did not look much like hostility, nor did I really suspect any. The garrison had been re-enforced (being about 200 men), the post fortified to some extent, guns loaded and matches lighted on our approach; yet there did not appear any hostile intent toward us, as the explanation for all this was, that they "had heard that I had orders to attack and take Fort Clark. "

From this point rumors daily reached me, but so indefinite and contradictory as to afford no sure ground for hostile action on my part; and by taking such I could not know but I should be the first to break the treaty under which we were marching.

On reaching Uvalde, on the 5th (near Fort Inge), I felt more apprehension of hostility, though rumors were still very contradictory. To attempt, from this point, to return to New Mexico for the purpose of saving the command would have been impracticable, for I had but five days' rations, and our transportation was too much broken down to make the march without corn (which could not be had), even if everything but subsistence and ammunition had been abandoned. Behind us was the mounted force at Fort Clark, and a large mounted force said to be at San Antonio, reported to be from 700 to 2,000. At this time the only other method of escape left was to cross the Rio Grande, this being easy of accomplishment, but of very doubtful propriety, particularly as it was yet uncertain whether we should not only break the treaty with Texas, but also compromise the United States with Mexico by crossing troops into her soil.

On the 6th, while continuing our march, we heard that those companies at the coast had been disarmed, and that in all probability we would be also on our arrival there; that there would be a force of from 2,000 to 6,000 men against us. We then had no course open to us but to proceed, and, unless overpowered by numbers, to endeavor to fight