  We consider causal 3-dimensional triangulations with the topology of
$S^2\times [0,1]$ or $D^2\times [0,1]$ where $S^2$ and $D^2$ are the
two-dimensional sphere and disc, respectively. These triangulations consist of
slices and we show that these slices can be mapped bijectively onto a set of
certain coloured two-dimensional cell complexes satisfying simple conditions.
The cell complexes arise as the cross section of the individual slices.
