By the time Gerald of Wales arrived in Ireland in the 12th-century, full of credulity for marvels and aberrations, the Irish tradition of scholarship was already ancient. As I have described in Climbing Brandon, the early Irish Christians married the new Mediterranean mystery religion with a prior druidic nature worship, yielding a faith in which God was more immanent than transcendent -- a Christian pantheism, as it were. One of the thorniest problems they faced was how to account for the miracles of scripture within the context of respect for nature and nature's laws.
The person who tackled this problem most effectively was the 7th century monk known as Augustinus Hibernicus, the "Irish Augustine." He tried to show that most of the miracles of scriptures could be accounted for within the framework of nature -- God modifying the temporal unfolding of events, but not acting against nature itself.
For example, when the Israelites were in Egypt, God changed water into blood in an instant, and made salt water sweet when it was touched with a staff. Both things happen naturally, noted Augustinus Hibernicus. Our bodies change the water we drink into blood, and salt water becomes sweet when it passes through clouds or earth. So, in both cases, God did not so much set aside the laws of nature, as employ them for his purposes.
Augustinus had more trouble accounting for, say, Moses' rod turning into a serpent, since he knew of no example in nature where plant becomes animal. Here he was inclined to believe the "miracle" was some sort of hallucination -- both rod and serpent actually being made of earth, for instance.
Now all of this sounds far-fetched, but it is not the same sort of credulous embrace of the supernatural that we find in Gerald of Wales. Augustinus accepted the stories of the Bible as reliable accounts, and struggled to show that they could be accounted for within the natural order: God created the universe, and thereafter felt no need to set aside the laws of his creation. This is a rather remarkable affirmation for the 7th century, and stands in stark contrast to the supernatural/natural dualism that characterized continental Christianity. It is perhaps not too much of a stretch to count Augustinus an early religious naturalist -- allowing him, of course, the conceptual limitations of his time.
For Augustinus, there is no miracle except the creation itself. As the scholar John Carey says of the world view of Augustinus and his Irish contemporaries: "Existence itself, then, is the ultimate miracle: had our eyes not grown so dull, they would be dazzled with ineffable wonder wherever we turned our gaze."