[andrewflnr]

The mantle is officially "solid" (as proven, I believe, by propogating shear waves, which an actual liquid cannot do). It flows, but very slowly. Very very slowly. I'd say that big chunks of material staying intact over billions of years is, in fact, an illustration of just how slowly.

[tabtab]

Wikipedia: "[The mantle] is predominantly solid but, on geologic time scales, it behaves as a viscous fluid, sometimes described as having the consistency of caramel."