The influence of the term is-proportional-to B2 on the electron in the
hydrogen atom in a weak uniform magnetic field is investigated. The s
eparation of fast and slow motion is carried out and the analytical so
lution of the averaged problem is constructed. The equations of fixed
trajectories for arbitrary L(z) are obtained. The influence of the fas
t phase term in the Hamiltonian on the stability of these trajectories
is discussed. The origin of the stochastic layer is discussed and the
formulae for its width is derived.