From Washington — position of the Armies--General Pattersen in Martinsburg — another mistake, &c.
Washington, July 6.
--Messrs. Cameron and Fremont have gone to Fortress Monroe.
Reliable information, by telegraph, states that General Johnston (in command of the Confederate forces) is seven miles below Martinsburg in force.
No general advance has yet been made.
The Southerners, however, are gradually approaching the Federal lines.
It is understood that a general Federal movement will take place next week.
Latest.-- July 6, P. M.
--General Patterson's whole force is at Martinsburg.
The Federal pickets had fired on each other, and ten of their men were killed.
General McClellan was reported within two days march of Martinsburg.
General Johnston had approached within three miles of Martinsburg, with four thousand less than the Federal forces at that point. 