Canal injured by Confederates, August 1864.

Chesapeake & Ohio Canal. - This great public work was injured by the late Confederate raids to such an incalculable extent that it is almost impossible to tell when navigation will be resumed. It appears that at the lower end of the Canal they took especial pains to do as much damage as possible. The aqueduct at the mouth of the Antietam was very materially damaged by throwing off the heavy stone walls which form the trunk, and boring holes through the archway. Lock No. 40 was also considerably injured by the walls having been excavated and thrown in. The original materials of these works, however, consisting of dressed blocks, will be lifted by derricks from the depths below and again put in place, and thus the work will be more speedily reconstructed than otherwise would be the case. The damage done to other locks is confined to the destruction of the wooden gates. A number of the culverts have been blown up and otherwise destroyed. In addition to the damages done to the Canal itself, between seventy and eighty boats have been burned, so that when navigation is again resumed the facilities for transportation will, we fear, be greatly inadequate to a vigorous prosecution of the coal trade.