charges of powder-two in each dam-and each of 500 pounds sunk at a depth of seven feet from the surface. These will be so arranged that the radii formed by each will overlap each other about the center of the dam. These charges will be inclosed in gutta percha cylinders thirty inches in diameter and thirty inches high, and exploded by means of the Gomez fuse. I have now at work a dredging machine excavating on the water side (south), designing to make a hole nearly thirty feet deep, so as to receive the debris from the explosion, and leave sufficient depth of water afterward.
On the enemy's side of the gap the shore is very bold, and we rely on the representations of Professor Maillefert, now on duty with the navy, who says that it is perfectly possible to deepen the water to any extent by exploding torpedoes under water on the bottom. The length of river navigation saved by this cutting will be four miles and threequarters as compared with 500 feet.
The number of days that work has been going on this month is eighteen-the day's work being represented by 150 men working twelve hours, with the assistance of twenty carts, twelve two-horse wagons, and six four-horse plows. The enemy annoy the working parties by mortar and other firing, although their pickets are quiet and harmless. The signal tower on the James River at the Crow's Nest, nearly opposite Dutch Gap, is now completed, being 126 feet high and capable of being made forty feet higher if required. This was constructed by Company D, First New York Volunteer Engineers, Captain Hartmann.
A wharf has been built on the Appomattox and one on the James River, together with several roads and other minor engineering details at different places.
I have as yet received no report of engineer operations on the Eighteenth Army Corps front (now the Tenth Army Corps), and can only say that it consists principally in erecting strong redoubts connected by strong curtains along the whole front.
Listening galleries have been run from the redoubt near the Hare house in anticipation of the enemy's running in that direction. As yet, however, no indications have been seen.
Captain Francis U. Farquhar, U. S. Engineers, was relieved from duty in this department about the 22nd of August. Captain George L. Gillespie, U. S. Engineers, was appointed chef engineer for the Eighteenth Army Corps front at Petersburg,, by orders from the headquarters Army of the Potomac. First Lieutenant William R. King, U. S. Engineers, is on duty in this department at New Berne, N. C. First Lieutenant Charles B. Phillips, U. S. Engineers, became, sick and is now on leave of absence.
I have the honor to transmit also the following photographs and drawings, viz:*
Numbers 1. One photographic copy of Redoubt Anderson (Numbers 3), viewed from its front.
Numbers 2. One photographic copy of Redoubt McConihe (advanced in front of Numbers 3), viewed from the interior.
Numbers 3. One photograph of the excavation at Dutch Gap, August 20, nine and one-half days' progress, viewed from the south side.+
Numbers 4. One photograph of same taken on September 5, twenty-three days' progress, viewed from the same position.+
Numbers 5. One photograph of Parrott gun battery forming the right of the entrenchments for the protection of Dutch Gap.
*To appear in the Atlas.