  The formation of pyramid-like structures in thin-film growth on substrates
with a quadratic symmetry, e.g., {001} surfaces, is shown to exhibit
anisotropic scaling as there exist two length scales with different time
dependences. Analytical and numerical results indicate that for most
realizations coarsening of mounds is described by an exponent n=0.2357.
However, depending on material parameters, n may lie between 0 (logarithmic
coarsening) and 1/3. In contrast, growth on substrates with triangular
symmetries ({111} surfaces) is dominated by a single length scale and an
exponent n=1/3.
