I. The channel of the Delaware river, from a line drawn across said channel, from a granite monument erected upon the eastern bank of said river in the year 1882, by the joint boundary commission of the states of New Jersey and New York to mark the western extremity of the boundary line between said states of New Jersey and New York, in a westerly prolongation of said boundary line up and along said channel of said Delaware river as it winds and turns, for a distance of eighty-five miles or thereabouts, to a line drawn east across said river from a granite monument erected upon the west bank of said river in the year 1884, by H. W. Clarke and C. M. Gere, to mark the eastern extremity of the first line hereinafter described, shall continue to be a part of the boundary or partition line between the said two states: Provided however, That the limit of territory between the said two states shall be the center of the said main channel: And provided further, That each state shall enjoy and exercise a concurrent jurisdiction within and upon the water of said main channel between the lines of low water at either bank thereof, between the limits hereinbefore mentioned.