AN ORDINANCE to dissolve the union between the State of South Carolina and other States united with her under the compact entitled "The Constitution of the United States of America."
We, the people of the State of South Carolina, in convention assembled, do declare and ordain, and it is hereby declared and ordained, That the ordinance adopted by us in convention on the twenty-third day of May, in the year of our Lord one thousand seven hundred and eighty-eight, whereby the Constitution of the United States of America was ratified, and also all acts and parts of acts of the General Assembly of this State ratifying amendments of the said Constitution, are hereby repealed; and that the union now subsisting between South Carolina and other States, under the name of the "United States of America," is hereby dissolved.
Done at Charleston the twentieth day of December, in the year of our Lord one thousand eight hundred and sixty.
Source: Official Records, Ser. IV, vol. 1, p. 1.
From "Ordinances of Secession" at constitution.org
According to Wikipedia, "An official secession convention met in South Carolina following the November 1860 election of Abraham Lincoln". The convention issued the above "ordinance of secession" on 20 December, 1860, and ordered seven members to draft a separate statement, which was adopted by the convention on Christmas Eve as "The Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina from the Federal Union" (hereinafter "The Declaration").
...an increasing hostility on the part of the non-slaveholding States to the institution of slavery, has led to a disregard of their obligations, and the laws of the General Government have ceased to effect the objects of the Constitution. ... The State of New Jersey, at an early day, passed a law in conformity with her constitutional obligation; but the current of anti-slavery feeling has led her more recently to enact laws which render inoperative the remedies provided by her own law and by the laws of Congress. In the State of New York even the right of transit for a slave has been denied by her tribunals; (emphasis mine)Regardless of questions of Constitutionality, South Carolina's Declaration makes it quite clear that slavery is the reason for their secession.
Part 1: The Confederate States of America and Treason
Part 3: Documenting Secession: Mississippi