merely weaving a series of supernatural terrors
The repetition of a note of disparagement ("merely weaving," "a mere
tale") in this and the succeeding sentence indicate that Shelley is
seeking from the first to distance Frankenstein from the tradition
of popular gothic fiction to which, in his own adolescence, he had
contributed two outlandish examples, Zastrozzi and St.
Irvyne, both published in 1810.