Seven-days' Battles at Mechanicsville to date of this report, including the movement from Richmond to the valley of Jackson and his forces and the re-enforcements sent to him from the army at Richmond, which information has been derived from statements made at these headquarters by spies, contrabands, deserters, refugees, and prisoners of war, in order of time as hereinafter indicated, and which at the time indicated were made the subject of special reports to you. I have also appended to and made it part of this report a varied summary of these forces and their movements, together with summary of the defenses in the vicinities of Richmond and Petersburg, showing the probable number of these forces and the position and strength of their defenses.

The summary of general estimates shows 200,000 men to have composed the rebel army of Richmond about the time of the Seven-days' Battle, which estimates are abundantly confirmed by the specific informations obtained up to date of this report, as will be seen by reference to the table showing organization of the rebel army accompanying and part of this report.

It is also shown that the rebel losses in the seven battles before Richmond in killed, wounded, missing, and prisoners was at least 40,000 men. It is also shown that General Jackson left for Gordonsville early in July with 40,000 men, and that at least as many more were sent to re-enforce him before the 10th of August, thus leaving the entire rebel force in the vicinity of Richmond and Petersburg, according to information received up to date of this report, 80,000 men.

The table of specific organizations of the rebel army shows that they had forty-six brigades, two hundred and fifteen regiments, nineteen battalions, and one company infantry, one legion, eleven regiments cavalry, two battalions, and six companies ditto, three battalions artillery, and seventy-six batteries of artillery; in all equaling two hundred and fifty-two regiments. Of course, in the nature of the case, this specific information does not cover their entire army, and must, therefore, be taken as below even a minimum estimate.

All of which, general, is respectfully submitted, by your obedient servant,

E. J. ALLEN.

Major General GEORGE B. McCLELLAN,

Commanding Army of the Potomac.

[Inclosure.]

DEFENSES OF RICHMOND.

The statements in this and previous reports show the number of fortifications for the defense of Richmond to be fifty-two, and that the number of guns mounted upon thirty-six of them is 201 to 205, while the number upon the remaining sixteen is not given. These fortifications are shown to be located about as follows: one fort on the plank road northwest of Richmond; one fort on Deep Run turnpike, near the fair grounds; one on Bacon Quarter Branch Creek, north of Richmond; four on Brook turnpike; one on road between Brook turnpike and Meadow Bridge road; three on Meadow Bridge road and Central Railroad; six on and near Mechanicsville turnpike; one on Union Hill; one on Race Course; one on Church Hill; three at and below Rocketts; one 3 miles below Rocketts, between River and Old River turnpike; two on Marion Hill; one on Fulton Hill; one at junction of Darbytown and Charles City roads; four on old stage road to Williamsburg;