The on delete cascade option is part of the constraint definition, not the delete command - here is a paste from the Oracle documentation (V7 unfortunately - the only one I have handy at the mo :( ), but it should apply equally to Oracle 8...
Maintaining Referential Integrity with the ON DELETE CASCADE Option
If you use the ON DELETE CASCADE option, Oracle7 permits deletions of referenced key values in the parent table and automatically deletes dependent rows in the child table to maintain referential integrity.
This example creates the EMP table, defines and enables the referential integrity constraint FK_DEPTNO, and uses the ON DELETE CASCADE option:
CREATE TABLE emp
deptno NUMBER(2) CONSTRAINT fk_deptno
ON DELETE CASCADE )
Because of the ON DELETE CASCADE option, Oracle7 cascades any deletion of a DEPTNO value in the DEPT table to the DEPTNO values of its dependent rows of the EMP table. For example, if department 20 is deleted from the DEPT table, Oracle7 deletes the department's employees from the EMP table.