Treated harmonically it is a second dominant formation, and should read C flat, D natural, A flat, diminished seventh of the key of the dominant.
"The So-called Human Race"
Bert Leston Taylor
Schubert does not, however, use it harmonically, otherwise the B natural would read C flat.
"The So-called Human Race"
Bert Leston Taylor
But Schubert, instead of progressing harmonically, goes directly back into the tonic of A flat major.
"The So-called Human Race"
Bert Leston Taylor