Our march was resumed the following day at ten o'clock A. M., and early in the afternoon we captured the "Quaker Guns" at Centreville. The enemy had actually placed in the earthworks or forts which commanded the road, large trunks of trees, resembling cannon of heavy calibre, which frowned down upon us from the heights. Had it not been for the information we had received from contrabands on the march, that the enemy had evacuated, a report confirmed by the curling smoke which rose from various parts of the field, this formidable array of threatening cannon would have terrified us all, and greatly retarded our progress. Indeed, it was not till after the suspicious works had been thoroughly scanned with field-glasses that we were ordered to advance, when the strong position was carried without the snapping of a cap, or a sabre stroke. Chagrin was written upon every face. Not a sign of the enemy was visible, save the deserted remains of their winter-quarters, which fell into our hands. A very brief halt was here made, and, hurrying our steps, we soon crossed the memorable Bull Run, and came up with the rearguard of the retiring army at Manassas Junction. Here we pitched into them, and kicked up a little dust on the road to Bristoe. This expedition, or wild-goose chase, was continued to Warrenton Junction, where General George D. Stoneman found the enemy in force, but returned without attacking them. Having loitered about these historic fields a few days, our whole force began to fall back towards its old position on the Potomac, establishing our advanced picket-lines, however, as far forward as Centreville, with Fairfax Court House as headquarters. Our line of pickets intercepts the Leesburg turnpike at Drainesville and extends to the Potomac, a distance of about twenty miles. GUERILLAS AND BUSHWHACKERS. As guerillas and their brethren, the bushwhackers, infest the country more or less, picketing is dangerous as well as difficult. Between the Rappahannock and the Potomac lies a vast territory which abounds in creeks, marshes, deep, dark forests, with only here and there a village or settlement. A little to the west of this plain extend the Bull Run Mountains, with their ravines and caverns. This is a very fit hiding-place for mischief-makers. The guerillas consist mostly of farmers and mechanics, residents of this region, who, by some means, are exempt from the Rebel conscription. Most of them follow their usual avocations daring the day, and have their rendezvous at night, where they congregate to lay their plans of attack on the pickets.