  We generalize the continuum model for Moir\'e structures made from twisted
graphene layers, in order to include lattice relaxation and the formation of
channels at very small (marginal) twist angles. We show that a precise
description of the electronic structure at such small angles can be achieved by
i) calculating first the relaxed atomic structure, ii) projecting the
interlayer electronic hopping parameters using a suitable basis of Bloch
states, and iii) increasing the number of harmonics in the continuum
approximation to interlayer hopping. The results show a complex structure of
quasi one dimensional states when a finite bias is applied.
