_July 23._--Our command was cheered to-day by the arrival of a large mail, which brought a message to nearly every man. During active campaigning, as in the invasion of Pennsylvania and Maryland, it is difficult to keep up postal connections with the civil world, and, with the very best efforts which can be made, our mails are greatly delayed, sometimes even for weeks together. But when they do come, they are hailed with a delight which is almost frantic. The post-boys are cheered as far as they can be seen, as they wend their way from camp to camp, with their horses loaded down with the enormously swollen mail-bags. Several bushels of letters are sometimes brought by one carrier, as was the case to-day.
During the day we have heard very heavy cannonading in the direction of White Plains. It appears that General Meade, misled by the information brought by some of his scouts, expected to engage the Rebel army in Manassas Gap, or west of that, where General Buford found the enemy in force. Our army was accordingly concentrated upon this point. The Third Corps, under General French, which occupied Ashby's Gap, was sent forward rapidly to Buford's support, where its First Division, commanded by General Hobart Ward, pushed through the Gap, driving the enemy before it, but with mutual loss. Here the New York Excelsior Brigade, General F. B. Spinola commanding, greatly distinguished itself, by making three heroic charges up the frowning steeps, where the Rebels were strongly posted. Their general was twice wounded. But the effort was a success.
On the morning of the twenty-fourth our soldiers pushed forward as far as Front Royal, but found no enemy. They then learned that they had been fighting only a portion of Lee's rearguard, which in the night had slipped away in the trail of their main army southward. By this move General Meade's army lost about two days' march; and when again we reached the bank of the Rappahannock, the old foe was facing us in threatening attitude from the opposite shore.
This afternoon the Harris Light was sent on a scout to Thoroughfare Gap. From the heights beyond the Gap we saw the wagon-train of the Eleventh Corps moving toward Warrenton. This was a portion of the force which had expected a fight at Manassas Gap.