Not far from Biere, the river Aubonne springs out at the bottom of an amphitheatre of rock, receiving additions soon after from a group of twenty natural pits, which the peasants call unfathomable--an epithet freely applied to the strange holes found in the Jura.

It is remarkable that the way seems to stand at different levels in the various pits.[24] The plain of Champagne, in which they occur, is unlike the surrounding soil in being formed of calcareous detritus, evidently brought down by some means or other from the Jura, and is dry and parched up to the very edges of the pits.

The Toleure, a tributary of the Aubonne, frequently large enough to be called a confluent, flows out from the foot of a wall of rock composed of regular parallelopipeds, and in the spring, when the snows are melting freely, its sources burst out at various levels of the rock.

Farther to the west, the Versoie, famous for its trout, pours forth a full-sized stream near the Chateau of Divonne, which is said to take its name (_Divorum unda_) from this phenomenon.

Passing to the northern slope of this range of the Jura, the Orbe is a remarkable example of the same sort of thing, flowing out peacefully in very considerable bulk from an arch at the bottom of a perpendicular rock of great height.