The Lectures on Faith were once included with the Doctrine and Covenant. It was dropped sometime before 1921. The 1921 edition of the Doctrine and Covenants reads:
Certain lessons, entitled "Lectures on Faith," which were bound in with the Doctrine and Covenants in some of its former issues, are not included in this edition. Those lessons were prepared for use in the School of the Elders, conducted in Kirtland, Ohio, during the winter of 1834-1835; but they were never presented to nor accepted by the Church as being otherwise than theological lectures or lessons. (here)
Here for full text at CenterPlace.org. Here for 1851 D&C. Here for Wikipedia article. Here for Encyclopedia of Mormonism.