The militia of Jersey were relied on to reinforce its garrison, and also to form a corps of observation which might harass the rear of any detachment investing the place.
[Sidenote: Measures taken by General Washington for cutting off supplies from Philadelphia.] To increase the inconvenience of General Howe's situation by intercepting his supplies, six hundred militia, commanded by General Potter, crossed the Schuylkill, with orders to scour the country between that river and Chester; and the militia on the Delaware, above Philadelphia, were directed to watch the roads in that vicinity.
The more effectually to stop those who were seduced by the hope of gold and silver to supply the enemy at this critical time, congress passed a resolution subjecting to martial law and to death, all who should furnish them with provisions, or certain other enumerated articles, who should be taken within thirty miles of any city, town or place, in Jersey, Pennsylvania, or Delaware, occupied by British troops.
These arrangements being made to cut off supplies from the country, General Washington reoccupied the ground from which he had marched to fight the battle of Germantown.
[Sidenote: Attack upon Fort Mifflin.] Meanwhile, General Howe was actively preparing to attack fort Mifflin from the Pennsylvania shore.

He erected some batteries at the mouth of the Schuylkill, in order to command Webb's ferry, which were attacked by Commodore Hazlewood, and silenced; but, the following night, a detachment crossed over Webb's ferry into Province Island, and constructed a slight work opposite fort Mifflin, within two musket shots of the block-house, from which they were enabled to throw shot and shells into the barracks.

When day-light discovered this work, three galleys and a floating battery were ordered to attack it, and the garrison surrendered.

While the boats were bringing off the prisoners, a large column of British troops were seen marching into the fortress, upon which the attack on it was renewed, but without success; and two attempts made by Lieutenant Colonel Smith to storm it, failed.

In a few nights, works were completed on the high ground of Province Island which enfiladed the principal battery of fort Mifflin, and rendered it necessary to throw up some cover on the platform to protect the men who worked the guns.
The aids expected from the Jersey militia were not received.