Article IV, Section 3, Clause 1

In the same article, section 3, it is provided, That new states may be admitted into the Union ; but no new state shall be formed or erected within the jurisdiction of any other state, nor any states be formed by the sanction of two or more states, or parts of states, without the consent of the legislatures of the states concerned, as well as of Congress. This section can be opposed by none who have the peace and happiness of the states at heart; for, by this section, the designs of those who wish to effect…

Cites "section 3" of article IV and reproduces this clause closely; the passage reads "sanction" where the clause has "Junction."

New States may be admitted by the Congreſs into this Union; but no new State ſhall be formed or erected within the juriſdiction of any other State; nor any State be formed by the junction of two or more States, or parts of States, without the conſent of the Legiſlatures of the States concerned, as well as of the Congreſs.

The paragraph prints Article IV, Section 3, Clause 1 of the Constitution as signed; the quoted words are the same as the clause's (apart from capitals and the long s), though the pamphlet's punctuation differs in places.

…land which remain uninhabited, or but thinly ſettled, and which are yet to be divided into new governments, lie on the ſouth-weſtern boundary; the ſouthern intereſt will be ſtrengthened by the Repreſentatives of the new States.

The paragraph, on "this section," speaks of the new governments and "the Representatives of the new States," which refers to the admission of new states in Article IV, Section 3, Clause 1.

It is not competent, in my judgment, for three fourths of the States to abolish that provision of the Constitution by which no new State shall be formed within the jurisdiction of any other State, nor any State be formed by the junction of two or more States, without the consent of the Legislatures, and give to the Congress thepower to subdivide orunite the States; norisit competent for three fourths of the States to amend the Constitution…

The paragraph quotes "that provision of the Constitution by which no new State shall be formed within the jurisdiction of any other State, nor any State be formed by the junction of two or more States, without the consent of the Legislatures".

Yet all these States so admitted into the Union, slaveholding and free, were admitted by a distinct resolution of Congress, in each case declaring that they were so admitted under the constitutional provision authorizing the admission of new States, because they had each adopted constitutions republican in form.

The paragraph names "the constitutional provision authorizing the admission of new States"; only Article IV, Section 3, Clause 1 fits.