phenomena in this neighbourhood, due to
the subterranean courses which the fissured limestone of the Jura
affords to the meteoric waters. 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. This river no doubt owes its origin to the
superfluous waters of the Lake of Brenets, which have no visible
outlet, and sink into fissures and _entonnoirs_ in the rock at the
edge of the lake. Notwithstanding that the lake is three-quarters of a
league distant, horizontally, and nearly 700 feet higher, the belief
had always been that it was the source of the stream, and in 1776 this
was proved to be the fact. For some years before that date, the waters
of the Lake of Joux had been inconveniently high, and the people
determined to clean out the _entonnoirs_ and fissures of the Lake of
Brenets, which is only separated from the Lake of Joux by a narrow
tongue of land, in the expectation that the water would then pass away
more freely. In order to reach the fissures, they dammed up the outlet
of the upper into the lower lake; but the pressure on the embankment
became too great, and the waters burst through with much violence,
creating an immense disturbance in the lake; and the Orbe, which had
always been perfectly clear, was tr