"Fishkill, March 27- -- Our post at Peck's-kill, since the removal of the militia of the eastern States has been, in a maimer, iu a defenceless situation ; there being o. ly part of two regiments stationed there, under the care of Gen McDougal, amounting to about 250 men. The enemy having received intelligence of tins formed an expedition thither, with a view to take or destroy the stores belonging to the continentals, that were deposited there. Accordingly, on Sunday last they appeared with a frigate, four transports and several other small vessels in the bay, and landed about 1000 men, with several pieces of cannon.

"General McDougal not thinking it prudent to hazard a battle with such an unequal force, and not having reasonable advice of the enemy's movement, was under the necessity of destroying their stores in order to prevent their falling into their hands, and retired about two miles into the pass in the highlands, carrying with hkn his baggage and military stores, his advanced guards being stationed at Cortlandt's house in the valley. The enemy, the same da}-, took possession of the village, and remained close in their quarters until the next day in the afternoon, when a party of them, consisting of about 200 men, possessed themselves of a height a little south of Cortlandt's. The general having received a reinforcement from % Col. Gansevoort's regiment, of about 80 men, under the command of Lieut. Colonel Willet, permitted them to attempt to dispossess the enemy from that eminence. Col. Willet having accordingly made the necessary disposition, advanced withliis small party with the greatest firmness and resolution, and made the attack. The enemy instantly fled, with the greatest precipitation, leaving three men dead on the field; and the whole body, panic struck, betook themselves to their shipping, embarking under cover of the night -- and by the last accounts, they had sailed down the river. .Before they embarked, they gave out they intended to Stop at Tarrytown on their way down, and attempt to destroy our magazine of forage at Wright's mills.