  To explain the rich structure of voids, clusters, sheets, and filaments
apparent in the Universe, we present evidence for the convergence of the two
classic approaches to gravitational clustering, the ``pancake'' and
``hierarchical'' pictures. We compare these two models by looking at agreement
between individual structures -- the ``pancakes'' which are characteristic of
the Zel'dovich Approximation (ZA) and also appear in hierarchical N-body
simulations. We find that we can predict the orientation and position of N-body
simulation objects rather well, with decreasing accuracy for increasing
large-$k$ (small scale) power in the initial conditions. We examined an N-body
simulation with initial power spectrum $P(k) \propto k^3$, and found that a
modified version of ZA based on the smoothed initial potential worked well in
this extreme hierarchical case, implying that even here very low-amplitude long
waves dominate over local clumps (although we can see the beginning of the
breakdown expected for $k^4$). In this case the correlation length of the
initial potential is extremely small initially, but grows considerably as the
simulation evolves. We show that the nonlinear gravitational potential strongly
resembles the smoothed initial potential. This explains why ZA with smoothed
initial conditions reproduces large-scale structure so well, and probably why
our Universe has a coherent large-scale structure.
