Complex sentence: A miracle is said to have occurred when the cross was still in the form of a log cut off from the broken mast; when lying on the shore an inhabitant of the village who had trampled on filth had cleansed his foot on this log.
Split into simpler sentences: A miracle is said to have occurred when the cross was still in the form of a log cut off from the broken mast. When the mast was lying on the shore, an inhabitant of the village who had trampled on filth had cleansed his foot on this log.