The bed of the same river, and the islands and dry land lying within the same, so as aforesaid assigned to this state, lying and being northerly of a line from the extremity of the boundary line of the counties of Philadelphia and Chester, at the bank of the river Delaware, to be extended across the same river, by a south-southeast course, to the shore of the state of New Jersey, are annexed to and shall be deemed to be, and shall henceforth be, parts of the county of Philadelphia, and of the several adjoining townships and precincts of the same county, lying along the said river.