  Previous models of dust growth in protoplanetary disks considered either
uniformly laminar or turbulent disks. This Letter explores how dust growth
occurs in a layered protoplanetary disk in which the magnetorotational
instability generates turbulence only in the surface layers of a disk. Two
cases are considered: a completely laminar dead zone and a dead zone in which
turbulence is ``stirred up'' from the MRI acting above. It is found that dust
is depleted from high altitudes in layered disks faster than in those cases of
a uniformly laminar or turblent disks. This is a result of the accelerated
growth of particles in the turbulent regions and their storage in the lower
levels where they escape energetic collisions which would result in disruption.
Thus the regions of a protoplanetary disk above a dead zone would become
rapidly depleted in small dust grains, whereas the outer regions, where the MRI
is active throughout, will maintain a small dust poplulation at all heights due
to the disruptive collisions and vertical mixing from turbulence. This
structure is similar to that which has been inferred for disks around TW Hydra,
GM Auriga, and CoKu Tau/4, which are depleted in dust close to the star, but
are optically thick at larger heliocentric distances.
