Movements on the Potomac.
--The Alexandria Gazette reports that the steamer
Anacostia, on Wednesday morning, towed to the Arsenal a large three-masted schooner, which she had captured off the mouth of
Pamunkey Creek.
The steamer soon after went down the river.
About nine o'clock, the steamer
Keystone State passed up. Several carriage guns were on her decks, and a full complement of seamen, but no troops were visible.--The steamer
Boston, accompanied by the propeller
Commercial, loaded with ammunition, also went by. No soldiers could be seen aboard them.
About 10 o'clock, a large propeller steamed down.
At 2 o'clock, the steamer
Powhatan went up. She had been down the river to replace destroyed buoys.