WASHINGTON, May 27, 1864.

Lieutenant-General GRANT,

In the Field:

GENERAL: Major-General Rosecrans' report of May 20, just received, shows that he has in Department of Missouri 20 regiments, 235 companies, and an aggregate present of 16,034, of which 14,718 are for duty. In the District of Saint Louis alone he has 5,877 present for duty. Of these (in District of Saint Louis) there are 54 companies of cavalry. In the whole department he has 179 companies of cavalry. What particular troops your ordered away I do not know; but I hardly think that all, if any, of your orders have been executed. In addition to the forces above enumerated there are always at the cavalry depot at Saint Louis a considerable number of dismounted and partly mounted cavalrymen who could be of service in case of any local disturbance. But from all I can learn there is no more danger now of a disturbance in Saint Louis than in Chicago or Springfield or Cincinnati. Indeed, the danger is lees, because no prisoners are kept there.

I have therefore ordered from that place down the Mississippi River, to General Canby, the Seventh Kansas Cavalry, ten companies; the Twelfth Missouri Volunteer Cavalry, twelve companies; the Sixty-eighth U. S. Colored Infantry, ten companies, and Tenth Kansas Volunteer Infantry, ten companies. If the cavalry cannot be fully mounted, they will go as infantry. I mean to follow up this order by telegraph till it is executed. More troops can well be spared from that department if we succeed in getting these away. When General Canby went West, any troops from Missouri, and General Rosecrans was directed to obey such orders. Canby ordered him in the name of the Secretary to send from 4,000 to 6,000 men down the Mississippi; but Rosecrans refused to do so, on the ground that the Secretary of War could not authorize Canby to use his name, and that you had decided that he had no troops to spare. The President has now placed Missouri in the Military Division of West Mississippi and directed that General Canby's orders must be obeyed. Whether General Rosecrans will obey these orders remains to be seen.

Very respectfully, your obedient servant,

H. W. HALLECK.

WASHINGTON, D. C., May 27, 1864-2.30 p.m.

Major-General ROSECRANS,

Saint Louis:

The Secretary of War directs that you immediately send down the Mississippi River to report to Major-General Canby the following regiments, viz: The Tenth Kansas Volunteer Infantry, the Sixty-eighth U. S. Colored Infantry, the Twelfth Missouri Volunteer Cavalry, and the Seventh Kansas Volunteer Cavalry. If the cavalry regiments cannot be immediately mounted and equipped as cavalry, one or both will be dismounted and equipped as infantry, and sent forward as such. You will see that these regiments are sent with proper amount of provisions, ammunition, and other supplies. You will telegraph daily to the Adjutant-General of the Army the progress made in forwarding these regiments till they all leave your department.

H. W. HALLECK,

Major-General and Chief of Staff.