On Sunday, the 24th, Colonel Sibley's force at St. Peter, was augmented by the arrival of about two hundred mounted men, under the command of William J. Cullen, formerly superintendent of Indian affairs, called the Cullen Guard. On the same day six more companies of the Sixth arrived, making up the full regiment, and also about one hundred more mounted men, and several squads of volunteer militia. The mounted men were placed under the command of Col. Samuel McPhail. By these acquisitions Colonel Sibley's command numbered about 1,400 men. Although the numerical strength was considerable, the command was practically useless. The ammunition did not fit the guns of the Sixth Regiment, and had to be all made over. The horses of the mounted men, were raw and undisciplined, and the men themselves were inexperienced and practically unarmed. It was the best the country afforded, but was probably about as poorly equipped an army as ever entered the field--and to face what I regard as the best warriors to be found on the North American continent; but fortunately the officers and men were all that could be desired. The leaders of this army were the best of men, and being seconded by intelligent and enthusiastic subordinates, they soon overcame their physical difficulties; but they knew nothing of the strength, position or previous movements of the enemy, no news having reached them from either Fort Ridgely or New Ulm. Any mistake made by this force, resulting in defeat, would have been fatal. No such mistake was made. Having now shown the principal forces in the field, we will turn to the movements of the enemy. The Indians felt that it would be necessary to carry Fort Ridgely and New Ulm, before they extended their depredations further down the valley of the Minnesota, and concentrated their forces for an attack on the fort. Ridgely was in no sense a fort. It was simply a collection of buildings, principally frame structures, facing in towards the parade ground. On one side was a long stone barrack and a stone commissary building, which was the only defensible part of it. THE ATTACK ON FORT RIDGELY. On the 20th of August, at about 3 p. m., an attack was made upon the fort by a large body of Indians. The first intimation the garrison had of the assault was a volley poured through one of the openings between the buildings. Considerable confusion ensued, but order was soon restored. Sergeant Jones attempted to use his cannon, but to his utter dismay, he found them disabled. This was the work of some of the half-breeds belonging to the Renville Rangers, who had deserted to the enemy. They had been spiked by ramming old rags into them. The sergeant soon rectified this difficulty, and brought his pieces into action. The attack lasted three hours, when it ceased, with a loss to the garrison of three killed and eight wounded.