OMAHA, August 23, 1864.

Brigadier General ROBERT B. MITCHELL,

Fort Kearny, Nebr. Ter.:

Citizens in from Elkhorn report that on Sunday, 21st, Indians drove off 200 head of stock cattle from the Cut-Off Island, above mouth of Elkhorn. They report that the Indians are in force at Smith's Grove. Settlers in that region are all coming in the Elkhorn. I can get no intelligible account of the number, &c., of the Indians supposed to be there. Gavin Mitchell started yesterday morning without giving me notice. The Governor starts a company from here to the Cut-Off this morning.

JNO. PRATT,

Assistant Adjutant-General.

WASHINGTON, D. C., August 23, 1864.

Governor JOHN EVANS,

Denver, Colo. Ter.:

The Secretary of War directs me to say that a recent law requires all cavalry horses to be purchased under direction of Colonel Ekin, of the Quartermaster's Department. If there is such a pressing necessity that purchases cannot be made in time the military authorities can resort to impressment. General Curtis is the proper judge of such necessity in his department.

H. W. HALLECK,

Major-General and Chief of Staff.

DENVER, August 23, 1864.

Major S. S. CURTIS:

Have five notorious guerrillas. Will try by military commission. If convicted can I approve, and shoot them?

J. M. CHIVINGTON,

Colonel, Commanding.

CAMP ON ARKANSAS RIVER,

Twenty-five miles below Crossing, August 23, 1864.

COMMANDING OFFICER,

Fort Union, N. Mex.:

I have the honor to report that near Red River I met four trains returning, who reported that a train had been attacked, taken, and five men killed on Lower Cimarron. I offered the trains escort, but they declined returning. Near Palo Blanco met Shoemaker's train, who returned with me. At Arroyo Vegas met Waters' train with two others. Waters returned; the others declined. Near Rabbit Ear met Samson's trains, that had come through; reported having been attacked near Upper Crossing of Cimarron, losing 130 mules; the freight was being brought in by returning ox trains. Found the remains of the rive men at Lower Cimarron scattered over the prairie, which I had buried. On my arrival here to-day found camped two trains for Fort Lyon, one for Fort Garland, one for Fort Union, and one citizen train for Taos. These trains while in camp here on the 21st instant were attacked by Indians, killing the wagon-master of contractor's train, Fort Union, Numbers 48,