On the 24th, accompanied by Captain Mendell and Lieutenant Howell, I made a reconnaissance of the country between the Avery house and the Blackwater Swamp, for the purpose of selecting a line to fall back upon in the event of withdrawing a part of the army for other purposes. The crossings of the swamp were also carefully searched, and its character examined in regard to forming an obstacle to the passage of artillery and infantry.

On the 29th the Appomattox was also examined in reference to the facilities for bridging it.

General Sheridan's expedition toward Gordonsville returned on the 30th, and the assistants who accompanied it brought back most valuable topographical information, among other interesting matter a survey of the lines of the enemy's works at Spotsylvania Court-House. This latter enables me to furnish in full, and with accuracy, the battlefield map of that locality. Surveys were daily made of the different lines taken up, and reconnaissances were extended over the adjacent country. The extreme heat and dust greatly interfered with their advancement.

Lieutenant Howell was temporarily, during the 28th, 29th, and 30th, on duty with the Sixth Corps, and Lieutenant Benyaurd, for the last few days of June, with the Ninth Corps. Captain Gillespie was engaged also at this time with the different corps in examining and rectifying their lines.

During the month of July the officers of engineers were principally occupied in superintending the various operations of their profession, such as the preparation of siege material, the construction of redoubts, batteries, parallels, and boyeaux, together with conducting the necessary surveys, and preparing complete plans and maps of the envious of the city and its approaches incident to offensive movements against the fortified position taken up by the enemy in front of Petersburg. No regular siege was intended, as it would be impossible, with the small army brought before it, to invest it completely. The lineal contour is too great to attempt to cut off all communications with the town, or to prevent re-enforcements being thrown into it. To take the place some favorable position must be selected at which to assault the works and burst through and occupy the interior, and to accomplish this a preponderance of metal must be brought to bear against the immediate point of attack to silence the enemy's guns, and to open the way for an attacking column specially chosen for the occasion. The new era in field-works has so changed their character as in fact to render them almost as strong as permanent ones, and the facility with which new and successive lines of works can be constructed (so well proven throughout the whole campaign just terminated) renders it almost useless to attempt a regular siege. The open assault of works is attended with immense loss of life, but at the same time during the slow operations of the siege the sharpshooters so effectually does his work as to produce a large bill of mortality.

On the 3rd of July the major-general commanding addressed a communication to the chief of artillery and chief engineer to know "whether any offensive operations from he lines now held by this army are practicable." The commanding general of the Ninth Corps had authorized Lieutenant-Colonel Pleasants, commanding the Forty-eight Regiment Pennsylvania Volunteers, to drive a gallery for a mine to blow up one of the enemy's batteries in his front, and the above officers were also directed to examine the place and ascertain whether on assault could be advantageously made, should the operation prove