Acting Brig.-Gen. James E. Mallon. Acting Brig-Gen. MALLON, (of the Third brigade, Second division, Second corps, Army of the Potomac,) killed in action at Bristoe Station, Wed- nesday, Oct. 14, was of Irish-American parentage, and born in the City of Brooklyn, Sept. 12, 1836. Having received a good commercial education, he was employed first, about eleven years ago, in the house of WRIGHT, GILLET &RAWSON, and subsequent- ly in the firm of HOLCOMB & HARVEY, both in the wholesale commission business in the City. A few years antecedent to the outbreak of the rebellion, he commenced the same line of business on his own account, and speedily secured for himself an honor- able position on the floor of the Corn Exchange, and of the new Produce Exchange. No one of the younger class of merchants was more widely known or more highly esteemed that Mr. MALLON. He was a most intelligent, energetic and upright business man, faithful in the performance of all his duties, and scrupulously exact in all his mercantile transactions. Having been a member of the Fourth Company (Capt. ROBLET) Seventh regiment, N.Y.S.N.G., for many years prior to the present war, he cheer- fully responded to what he regarded as the impera- tive call of his country, and waiving all other consid- erations, he went with his regiment as a private in the ranks, in April, 1861, to Washington. On its re- turn, after its first month's service--not anticipating any further participation of the regiment in the struggle, and enthusiastically eager to do his share of patriotic duty to the Re- public--of whose history he had been a dili- gent student, and in whose position among the na- tions he felt a robust pride--he joined as a First Lieu- tenant, the Fortieth New-York Volunteer (Mozart) regiment, then commanded by his brother-in-law, Col. J.J. REILLY. After the Army of the Potomac had been trans- ferred to the Peninsula, last year, Lieut. Mallon re- ceived the complimentary appointment of Aid from the late Gen. KEARNY, and for some time acted in the capacity of Assistant Adjutant-General on the gallant General's Staff. Of this appointment--which was specially designed as a recognition of his intelligence and intrepidity--Lieut. MALLON was very justly proud, coming as it did from so distinguished an offi- cer of his own race as Maj.-Gen. PHILIP KEARNY. Soon after the death of KEARNY, Lirut. MALLON was transferred by Gov. MORGAN from the Mozart to the Tammany (Forty-second New-York Volunteers) reg- iment, and promoted to the rank of Major for gal- lantry and efficiency. On the reorganization of the Army of the Potomac, under Gen. BURNSIDE, Maj. MALLON was detached from his regiment and assigned to the position of Acting Assistant Provost-Marshal of HOOKER's Grand division. He was subsequently detailed for the per- formance of the same duty, in connection with the Secord corps, then under Gen. COUCH. On the death of the second Colonel of the Forty- second, and on the direct and earnest recommenda- tions of Gen. HOOKER, (then in command of the Army of the Potomac,) as also of his immediate corps, division and brigade commanders, Maj. MALLON was raised to the Colonelcy of the regiment by Gov. SEY- MOUR, against decidedly strong political pressure in favor of another officer. Col. MALLON'S commission moreover, was dated St. Patrick's Day, 1863, a trivial circumstance in itself, but very agreeable to his feelings. He commanded his regiment in the battle of Gettysburgh in July, and that during that terrible conflict was repeatedly under the immediate personal leadership of Maj.-Gen. MEADE, who had swung round from corps to corps, according to the necessi- ties of each, the veteran fighting brigade, which in- cluded Col. MALLON'S regiment. In subsequent con- versing with the present writer about the glorious victory of July, Col. MALLON was most enthusiastic in his eulogy of the coolness, skill and valor of Gen. MEADE, to whom he referred as an illustration of his high ideal of a most accomplished soldier. On the retreat of LEE'S army to the south of the Potomac, Col. MALLON was detached, with orders to proceed to New-York and secure a reinforcement of conscripts for his war-worn regiment. He was in this vicinity, in obedience to his instructions, through the months of August and September. Some three weeks ago, he once more and haplessly for the last time bade farewell to his friends, to rejoin his com- mand in season, as he himself expressed it, "for the next fight." It was his last fight. His death was caused by a gunshot wound in the stomach, which unfortunately proved fatal in half an hour. He closed his brief career gloriously, as became so noble a citizen-soldier. He had often spoken to the writer, of the enviable death of his former chief, the lamented KEARNY. He felt the full force of a favorite poet's words-- "Whether on the scaffold high, Or in the battle's van. The noblest place for a man to die, Is where he dies for man." As KEARNY fell, so "in the battle's van," and in the same glorious cause, fell the youthful and chivalrous MALLON. A braver soldier, a truer patriot, a more perfect gentleman never drew a breath of life. He leaves an aged mother and a young wife, with two small children, to bear the affliction of a most heart- rending bereavement. Gen. MALLON was about five feet seven inches high, and of remarkably sinewy frame. His manly features were most expressive of the rare qualities of mind and soul, to which were traceable the causes which led to his rapid promotion from the position of a private soldier, in the leadership of one of the most efficient brigades in the service of the Republic. In religion, Gen. MALLON, like all his family, was a Catholic; in political conviction he was a Conserv- ative Republican; but he never had anything to do with, had no taste for, practical politics. His remains reached the residence of the family in Little Water-street, Brooklyn, on Monday, under the care of his brother, Lieut. Thomas MALLON, who was himself very seriously wounded in the battle of Gettysburgh. His funeral, which will take place early to-day, (Wednesday), will be strictly private, in obedience to the frequently expressed wishes of the fallen hero. M.H.