AUGUST 4-7, 1862.-Reconnaissance from Jacinto to Bay Springs, Miss.,

and skirmish.

Report of Brigadier General Robert B. Mitchell, U. S. Army, commanding First Brigade, Fourth Division, Army of the Mississippi.

HDQRS. FIRST Brigadier, FOURTH DIV., ARMY OF THE MISS., Iuka, Miss., August 9, 1862.

GENERAL: I have the honor to report that, in obedience to orders received from your headquarters, I proceeded on the morning of the 4th instant with all my command, excepting the Thirty-fifth Illinois Volunteers and one section of the Eighth Wisconsin Battery, in the direction of Iuka, Miss., 12 miles.

Having dispatched a messenger to that point, he returned during the night with a dispatch from Lieutenant-Colonel Miles, commanding the post, stating that no danger was apprehended in that quarter; whereupon, in accordance with previous advice with you and believing the enemy were concentrating a large force in that locality, I determined to make a reconnaissance in force toward Bay Springs, thereby cutting off any force that might be approaching Iuka.

Upon the road to Bay Springs, about 12 miles out, we upon the enemy's scouts, and pressed them so closely that they left their horses, horse equipments, coats, and accouterments, and took refuge in the brush and made their escape. It is proper here to state that I made my marches in the night, in consequence of the extreme heat during the day. I bivouacked that night at 1 o'clock about 10 miles from Bay Springs, hoping to reach them by daylight, but the infantry was so exhausted by the previous night's march that it was impossible for me to do so. After resting two hours I moved on as rapidly as possible, and within about 2 1/2 miles of Bay Springs the enemy's pickets fired upon my advance. I immediately deployed two companies of the Twenty-fifth Illinois Volunteers as skirmishers and scoured the brush until the pickets were discovered. Lieutenant Hunt, who had kindly volunteered his services as aide-de-camp, being near by on horseback, followed them up rapidly, wounding 1 severely and took the other prisoner. Here the roads forked, and I sent Colonel Post, of the Fifty-ninth Illinois Volunteers, with five companies of the Twenty-fifth Illinois and one section of Carpenter's [Wisconsin] battery, with two companies of the Seventh Kansas Cavalry, Captains Swoyer and Gregory, to Bay Springs, going myself with the balance of my command to Rogers', 2 1/2 miles south of the Springs, where the main encampment was said to be, attacking the enemy in the rear. My skirmishers followed them up closely, but I found them experts on a retreat. After driving them some 3 miles and scattering them in every direction I concluded, in consequence of the exhausted condition of the men, to abandon the pursuit. Shortly after I had ordered in my skirmishers a small party showed themselves in the timber near half a mile distant. Captain Carpenter unlimbered a 12-pounder howitzer and gave them a few shells, killing 2 men and 1 horse at the second shot.

Colonel Post, on his approach to Bay Springs, had quite a lively fire opened on his advance, but it took but one volley from his gallant front to disperse the rebels and drive them to their favorite hiding place-the brush. We captured a number of prisoners, I think 15 in all, a list of which I have sent you with the prisoners, and, as far as can be ascertained, killed 2 and wounded several, 1 mortally. I rested for some time at Rogers', and dined my men on green corn, having no other