  We introduce a model to describe columnar phases of chiral discotic liquid
phases in which the normals to disc-like molecules are constrained to lie
parallel to columnar axes. The model includes separate chiral interactions
favoring, respectively, relative twist of chiral molecules along the axes of
the columns and twist of the two-dimensional columnar lattice. It also includes
a coupling between the lattice and the orientation of the discotic molecules.
We discuss the instability of the aligned hexagonal lattice phase to the
formation of a soliton lattice in which molecules twist within their columns
without affecting the lattice and to the formation of a moir\'{e} phase
consisting of a periodic array of twist grain boundaries perpendicular to the
columns.
