_July 7._--Our cavalry is in the vicinity of Boonsboro', and is acting mostly on the defensive. The enemy in force is in our front, and an attack is momentarily expected. At six P. M. "to horse" was sounded throughout our camps; and, after waiting two hours in rain, ready for a move, orders were received to return to our quarters. Rain is now falling in torrents, accompanied with fearful thunderings and lightnings. Unpleasant as it is, we welcome its peltings, hoping that the storm will raise the Potomac above the fording mark, and thus give Meade an opportunity to attack Lee before he has time to recross the river into Virginia. We know that his pontoons at Falling Waters have been totally destroyed by our cavalry and by the high water, and that the only ford available is at Williamsport, and hence we welcome the falling floods. Many of us have to lie down in water, which, however, is not very cold. But the night is very tedious. _July 8._--The sun came out bright and warm this morning, enabling us in a few moments to dry our drenched blankets and garments. The roads, however, abound in mud, and the streams are enormously swollen. Early in the day our pickets were driven in along the Antietam, and the enemy advanced with such force that by noon the plains around Boonsboro' were the scene of a furious cavalry engagement. CAVALRY BATTLE AT BOONSBORO'. Dr. Moore, from whose excellent reports we have before quoted, gives the following graphic description of this cavalry duel: "Buford had the right and Kilpatrick the left. The movements of the cavalry lines in this battle were among the finest sights the author remembers ever to have seen. It was here he first saw the young general (Kilpatrick), and little thought that one day the deeds he saw him perform he would transmit to paper and to posterity. Here, all day long, the Rebel and the Union cavalry-chiefs fought, mounted and dismounted, and striving in every manner possible to defeat and rout the other. The din and roar of battle that, from ten A. M. until long after dark, had rolled over the plains and back through the mountains, told to the most anxious generals of them all, Meade and Lee, how desperate was the struggle--Stuart and his men fighting for the safety of the Rebel army, Buford and Kilpatrick for South Mountain's narrow Pass.