Does "them" refer to "similar occurrences" or does it refer to "Spiritual manifestations"?

Does "them" refer to "similar occurrences" or does it refer to "Spiritual manifestations"?

No class has shown itself so sceptical and incredulous of modern Spiritual manifestations as those very clergy who profess complete belief in similar occurrences in bygone ages, and their utter refusal to accept them now is a measure of the sincerity of their professions.

"The History of Spiritualism," by Sir Arthur Conan Doyle