Many contradictory opinions existed regarding the actual damage inflicted by the bombardment, as well as by the broadside fire of the passing fleet; and, Captain Porter desired Mr. Gerdes to make such a survey of Fort Jackson, as would settle all doubts touching the matter in question. Under his supervision, Acting Assistant Harris, aided by the other members of his party, traced in their corresponding places on the large existing detailed plan of the fort, all the injuries arising from the attack. Every hole in the ground, (whether caused by the mortar shells or round shot,) break in the walls, crack in the masonry, each gun dismantled or disabled, the burnt citadel, the hospital and outbuildings, the destroyed bridges and injured magazines, were noted by actual measurement.

The levees, which before the attack had kept the high water of the Mississippi from entering the fort, were found destroyed in numerous places by bomb-shells. Much of the area of the fort was in consequence overflowed. The number of balls and shells which fell in the inundated parts, was estimated from the proportion found in the dry parts. In the plan, the submerged parts were distinctly marked, and it plainly shows, that hardly one quarter of the whole area remained dry or above the level of the water.

From this survey the following statistics are gathered:

1. Number of 13 in. shells fired
from the mortar flotilla that fell
on solid ground1,113
2. Number of shells purposely
exploded over the forts1,080
3. Number of shells that fell in
overflowed ground (computed)3,339
4. Number of round shot visible
on dry ground fired from the
fleet and the gunboat of the
flotilla87
5. Number of round shot that
fell on overflowed ground
(computed)261
6. The total destruction of the citadel
of the forts, of the hospitals, the outbuildings,
the magazines, the bridges,
and of thirteen scows for use in the
moat.
7. The very severe injury to the ramparts,
particularly on the northwest side
to the casemates, all along the front,
(which were cracked from end to end,)
to the levees, which were completely
riddled, and to the works in general.
The demolition was so great, that the
shell holes in the ground left hardly
anywhere a free passage for walking.

It is further ascertained from this survey, that the armament of the fort consisted of fifty 32-pounders, seven columbiads, ten short guns, three rifle guns, two brass field pieces, and three mortars, in all seventy-five guns.

The following are extracts from Mr. Harris' report to Assistant Gerdes, accompanying the plan, which was published by the Navy Department:

'My informant, (an intelligent and reliable eyewitness,) voluntarily gave the credit of reducing the forts to the bomb fleet. The fort was so much shaken by this firing, that it was feared the casemates would come down about their ears. The loss of life by the bombs was not great, as they could see them coming plainly, and avoid them, but the effect of their fall and explosion no skill could avert.

'About one shell in twenty failed to explode; even those that fell in the water going off. It is worth noticing, that the bombs that fell in the ditches close to the walls of the fort and exploded there, shook the fort much more severely, than any of those that buried themselves in the soft ground.

'The fort was in perfect order when the bombardment commenced, the dirt which now disfigures everything is the accumulation of a few days. The water did not enter the fort until the levee had been broken by the bombs; during the summer of 1861, when the Mississippi was even higher, the parade ground remained entirely dry.'