the rapids
near Alexandria, and it would in all probability have been a complete
loss had it not been for the timely application of engineering skill
by Lieut. Col. Joseph Bailey, a civil engineer from Wisconsin, who
built a temporary dam across the river below the rapids and floated
out the entire fleet. This dam was over 750 feet long and in
connection with some auxiliary dams raised the water level some 61/2
feet. It was built under many difficulties, but by the skill and
ability of the engineer and the co-operation of the troops it was
completed in ten days. Another case was at the siege of Petersburg,
Va., where Lieut. Col. Pleasants, a Pennsylvania coal miner, ran a
gallery from our lines, under the rebel battery, some 500 feet
distant, and blew it entirely out of existence. The mine contained
four tons of powder and produced a crater 200 feet by 50 feet and 25
feet deep, and was completed in one month. The sequel to this was to
be an attack on the enemy's line through the gap made by the
explosion, and such an attack properly followed up would doubtless
have had a marked effect in shortening the duration of the war, but
this attack was so badly managed that it utterly failed and caused a
severe loss to our own army. The mine itself, however, was a great
success and produced a decided moral effect on both sides which lasted
until the end of the war.

It may be out of place to digress a moment to illustrate the moral
effect of such a convulsion. Several weeks after this great mine
explosion, the 18th Army Corps, to which I then belonged, was holding
a line of works recently captured from the rebels, about six miles
from Richmond, when one night the colonel commanding Fort Harrison, a
large field work forming a part of this line, came down to
headquarters and reported that some old Pennsylvania coal miners in
his command had heard mining going on under the fort. As the nearest
part of the enemy's line was some 400 yards from the fort, I was quite
certain that they could not have run a gallery that distance in the
time that had elapsed since we occupied the work, but there was of
course the possibility that the mine had been partly built beforehand
so as to be ready in just such a case as had arisen, viz., the capture
of the fort by our troops. I therefore went with the colonel up to the
fort to listen for the mining operations, and got the men who claimed
to have heard the subterranean noises, down in the bottom of