  The problem of formation of generic structures in the Universe is addressed,
whereby first the kinematics of inertial continua for coherent initial data is
considered. The generalization to self--gravitating continua is outlined
focused on the classification problem of singularities and metamorphoses
arising in the density field. Self--gravity gives rise to an internal hierarchy
of structures, and, dropping the assumption of coherence, also to an external
hierarchy of structures dependent on the initial power spectrum of
fluctuations.
