  Superconducting correlations in the two dimensional ${\rm t-J}$ model at zero
temperature are evaluated using numerical techniques. At the fermionic density
$\langle n \rangle \sim 1/2$, strong signals of $\dx2y2$ superconductivity were
observed in the ground state. These conclusions are based on a study of static
pairing correlations, the Meissner effect, flux quantization, and other
indicators of superconductivity. It is argued that these results can be
explained using a spin dimer ``liquid'' state. A phase diagram of the two
dimensional ${\rm t-J}$ model is presented.
