They told him that during the thunderstorm two cows and ten sheep had been killed there by lightning, which had scarcely injured the oak.
It was their custom to pile up a heap of stones wherever such an event occurred, to warn others from staying themselves, or allowing their sheep or cattle to stay, near the spot in thunder, as it was observed that where lightning struck once it was sure to strike again, sooner or later.

"Then," said Felix, "you may be sure there is water there!" He knew from his study of the knowledge of the ancients that lightning frequently leaped from trees or buildings to concealed water, but he had no intention of indicating water in that particular spot.

He meant the remark in a general sense.
But the shepherds, ever desirous of water, and looking on Felix as a being of a different order to themselves, took his casual observation in its literal sense.

They brought their tools and dug, and, as it chanced, found a copious spring.

The water gushed forth and formed a streamlet.
Upon this the whole tribe gathered, and they saluted Felix as one almost divine.