  Based on ROSAT PSPC pointed observations, we have determined the aggregate
X-ray shapes of 10 distant (z = 0.17-0.54) rich clusters: A2397, A222, A520,
A1689, A223B, A1758, A2218, A2111, A2125, and CL0016+16. Four of the clusters
have global X-ray ellipticities greater than 0.2, as measured on a scale of
diameter 3 h_{50}^{-1} Mpc. These strongly elongated clusters tend to show
substantial amounts of substructure, indicating that they are dynamically young
systems. Most interestingly, the global X-ray ellipticities of the clusters
correlate well with their blue galaxy fractions; the correlation coefficient is
0.75 with a 90% confidence range of 0.44-0.92. This correlation suggests that
blue cluster galaxies originate in the process of cluster formation, and that
the blue galaxy proportion of a cluster decreases as the intracluster medium
relaxes onto equipotential surfaces.
