From Washington.
Alexandria, Va., April 22
--The following is from the Gazette Extra, of this evening:
Washington,April 22 --About 1,200 men, including the Massachusetts regiment, are quartered at the Capitol.
All the Army and Navy officers from Virginia have resigned, or will resign.
Martial law is authoritatively said to be declared until there is evidence of approaching danger.
Major Haskins, of New York, is in command of Fort Washington, with 200 men.
It is estimated that 14,000 to 20,000 barrels of flour have been taken from Georgetown by the Government, and stored in the public buildings.
Numbers of families are leaving the city by every convenient route, deeming it unsafe to remain. 