The universal geography : earth and its inhabitants

THE TOLCANOES OF AUVEEGNE. 185
neighbour, the Puy de Pariou, is remarkable on account of the sharpness of the
brim of its crater. Farther north lies the dome-shaped Sarcouy, the clinkstone
of which is used in the manufacture of filters and glass. But the most curious
volcano of that region is the Puy Chopinc, a dome rising from a crater formed
of scoritD, and consisting of granite placed " like the ham of a sandwich " between
layers of basalt and trachyte. The range terminates in the north with two great
volcanoes, the Puys of Louchadiere and Xugere, from both of which immense
sheets of lava extend to the east or west. At Volvic there are vast quarries,
from which the towns in the neighbourhood procure most of their building
stones.
Most of the cones to the south of the Puy de Dome have craters on their
summits. The combined lava streams of the Puys of Lassola, de la "N'ache,
and Yichatel have dammed up the valley of the Yeyre, forming the Lake of
Aydat (2,710 feet), upon the borders of which stood Avitacum, the residence of
Sidonius Apollinaris. Amongst old volcanoes forther south are the Gravenoir
Fig. 140.—Volvic.
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MUo.
(" black gravel "), thus called from the colour of its ash, and the Tazanat, the crater
of which is occupied by a lake. Near Aigueperse there is a "poison spring"
discharging carbonic acid.
Numerous traces of volcanic activity are met with between the eastern slope
of this range and the plain of the Allier ; amongst others, the famous basaltic
plateau of Gergovia (2,440 feet), the ancient capital of the country, defended by
Vercingetorix against the legions of Julius Cnesar.
The integrity of many cones of the Auvergne is due, according to Sir Charles
Lyell, to the loose porous nature of the soil, which instantly ab.sorbs all moisture,
and thus prevents the formation of rills. The water thus absorbed is discharged
lower down as bounteous springs, some of which are valued for their medicinal
properties, whilst others cover the rocky surfaces over which they flow with a
coating of calc-taff, and incrustate all objects exposed to their action. The most
famous of these is that of St. Allyro at Clermont, which has built itself an aqueduct
250 feet in length, terminating in a superb arch thrown across the rivulet of Tire-