CULPEPER, January 25, 1864.

Colonel C. ROSS SMITH, Chief of Staff, Cavalry Corps:

A deserter from the enemy assigned to Mosby has come in, and he reports that the enemy's mounted cavalry is down toward Fredericksburg, their dismounted men doing picket duty in our front. Mosby is said to be at Markham, on Manassas Gap Railroad, with five companies of cavalry.

W. MERRITT,

Brigadier-General.

HEADQUARTERS ENGINEER BRIGADE,
Washington, D. C., January 25, 1864.

General J. G. TOTTEN, Chief Engineer:

SIR: I have the honor to forward the reports (delayed at first by the necessity of sending to the front, and since by other duties) in reply to the request of the Department of the 8th ultimo, desiring information as to the modifications that could advantageously be made in the fitting out of pontoon trains.

I now inclose the reports of three of my most experienced officers, each of which I can commend to the careful consideration of Mr. Trowbridge, while I have added to each special marginal notes of my own where they seemed to be advisable, the most important of which I may here recapitulate, with other opinions as to the substitute for general service of canvas-covered frame boats for the modified French pontoon now in use.

Generally, then, as to the modification of the bridge portion proper of the material, I feel I can safely recommend that the trestle so universally reported against shall be dispensed with hereafter, though I would retain the "saddle" timbers for the trains. I would dispense with the present claw-balks, using instead the ordinary balk, which in all cases should be cut one-half inch deep by one inch wide in two places, on opposite sides, at the proper distances near each end to receive the ropes that lash them together.

The claw pieces proposed by Lieutenant-Colonel Spaulding are often very convenient, but can generally be added by the troops using them, though in dispensing with the present claw-balks an equal number of common balks might have these claw pieces securely placed on them at the manufactory.

The chess in all cases should be riveted near each end and shoulder. The lashings, anchors and attachments of anchors, instruments, &c., should be as approved in the marginal notes, and a change not alluded to by these officers should be made in the chains attaching the boat to the hind wheels. The lower link of this chain should be a flat bar, say of 1/4-inch by 2-inch iron 1 foot long, so that no common chain link could hang below the top of the tire to catch and break the spokes.

The change in harness as suggested by Lieutenant-Colonel Spaulding, is important, doubtless, and whiffletrees in front of the wheel animals should, as far as possible, be dispensed with, and though not needed, as a reply to Mr. Trowbridge's letter I would say that nothing whatever can insure promptness and efficiency for pontoon trains till trained animals and drivers are kept expressly for them, while, for efficiency, with every bridge train on a march there should be a company of pontoniers mounted. One company so provided with