Bridges.The parts of this railroad-crossing over Bull Run near Union Mills, were of the standard size found most suitable for emergencies. This was fortunate, because the bridge was destroyed seven times. A work of this character could be put up in a very few hours. Repairing the masonry abutments, of course, consumed the greatest length of time, but even these grew like magic under the efforts of the construction corps. The lower photograph shows the same bridge reenforced with trusses. These standard size trusses and other parts of bridges were carefully made by the skilled engineers of the construction corps, and tested under weights greater than any they would conceivably be called upon to bear. These parts were kept constantly on hand so that repairs could be rushed at short notice.