But to hold the Maryland Heights we must also hold the Loudoun Heights, which are of the same elevation on the opposite side of the river and within cannon range. Six hundred men, I am advised, in possession of these (Loudoun Heights) by proper defneses, cn hold them-a thousand men certainly would do it. Bolivar Heights, which make the base of the triangle and over which any attack upon Harper's Ferry is likely to be made, held by a regiment and covered by artillery on the Maryland and Loudoun Heights, could hold them against any probable assault. The signal toward on Maryland Heights commands a view of the whole country, and no advance of troops could be made unless in night-time, w ithout notice, with these epositions well defended. I do not think there is any serious difficulty in reconstructing and protecting the railway there. There is, however, one point that will reuqire attention. The railway from Point of Rocks to Harper's Ferry, fifteen miles, is within cannon range for the whole distance. The road would necessarily be protected here-as one of [the] exposed points of the line-against a blockade by the enemy on the Virginia side of the river. The greater difficulty will be found, I apprehend, at or near Martinsburg. The railway enters the State of Virginia opposite Williamsport, twleve or fourteen miles. It offers a salient point of attack to which the energies of the enemy, now very active, would undoubtedly be directed. If we were to encounter the forces now at Winchester only, or in its vicinity, a brigade and a half intrneched in front of Martinsburg and on its flanks would be sufficient to protect the road across the line, w here it leaves the river, say from Harper's Ferry to Cherry Run, but it would reuire a large increase of artillery beyond what we now have, as well as other materials supports. A bridge across the Potomac at Williamsport, upon which our supplies would come at first, would be indispensable. I do not think it would be safe to commence the enterprise without this. There are, I learn from Mr. Spates, president of the canal company, about thirty flat-boats on the canal; not a sufficient number for the purpose. The railway from Hagerstown to Harrisburg would also be required for transportation. The company owns its engines, but no cars. These are all owned by traders in the towns on the line, so that these facilities would necessarily be supplies by the Government.

With sufficient artillery, the bridge and the rolling-stock of the rialway, and our men well intrenched in front of Martinsburg, I think we could hold and defend the line of railway with our present force against any assaults of the enemy, permanently posted at Winchester, Leesburg, or vicinity. But we cannot form a just opinion of this subject without contemplating the chances or the possibilities of sudden and large re-enforcements from Centerville or Manassas, via Strasburg, for a surprise of our forces or the destruction of some part of the road. It is not probable that any consideralbe column could move from Manassas in daytime without discovery from your lines; but whether by night, or by sending out detachments occupying two or three days in completing a movement, it might not be done, you will be better able to judge than we are here. We are informed that their railway is completed to Winchester. This would bring them within seven or eight miles of our outposts, and if by any movement they could thus strengthen their forces at Winchester, by the addition of 8,000 or 10,000 men, and strike us suddenly, although it may have taken them some days, it would present a different case. If your purpose were to occupy Winchester, such re-enforcement would be attempted. Whether it will be so at Martinsburg, I cannot so well form an opinion. If the