CHAPTER XXI.

A New Phase to our Military Problem.--General Johnston's Position.-- Defenses of James River.--Attack on Fort Drury.--Johnston crosses the Chickahominy.--Position of McClellan.--Position of McDowell.-- Strength of Opposing Forces.--Jackson's Expedition down the Shenandoah Valley.--Panic at Washington and the North.--Movements to intercept Jackson.--His Rapid Movements.--Repulses Fremont.-- Advance of Shields.--Fall of Ashby.--Port Republic, Battle of.-- Results of this Campaign.