  We establish upper bounds on the rate of decay of correlations of tower
systems with summable variation of the Jacobian and integrable return time.
That is, we consider situations in which the Jacobian is not Holder and the
return time is only subexponentially decaying. We obtain a subexponential bound
on the correlations, which is essentially the slowest of the decays of the
variation of the Jacobian and of the return time.
