  The squiral inflation rule is equivalent to a bijective block substitution
rule and leads to an interesting lattice dynamical system under the action of
$\mathbb{Z}^{2}$. In particular, its balanced version has purely singular
continuous diffraction. The dynamical spectrum is of mixed type, with pure
point and singular continuous components. We present a constructive proof that
admits a generalisation to bijective block substitutions of trivial height on
$\mathbb{Z}^{d}$.
