e of the Coiron, of the Ardeche, and of the Dordogne and
Chambon in the district of Mont Dore.

(_i._) _Dome-shaped Volcanic Hills._--I have previously (page 15)
referred to the two classes of volcanic eminences to be found in the
chain of the Puy de Dome; one indicated by the name itself, formed of a
variety of trachytic lava called "domite," and of the form of a dome;
the other, composed of fragmental matter piled up in the form of a
crater or cup, often ruptured on one side by a stream of lava which has
burst through the side, owing to its superior density. Of the former
class the Puy de Dome and the Grand Sarcoui (see Fig. 18) are the most
striking examples out of the five enumerated by Scrope, while there is a
large number, altogether sixty-one, belonging to the latter class. These
domes and crater-cones, as already stated, rise from a platform of
granite, either directly or from one formed of the lava-sheets of the
Mont Dore region, which in turn overlies the granitic platform. Of the
nearly perfect craters there are the Petit Puy de Dome, lying partially
against the northern flank of the greater eminence; the Puy de Cone,
remarkable for the symmetry of its conical form, rising to a height of
900 feet from the plain; and the Puys de Chaumont and Thiolet lying to
the north of the Puy de Dome. Of those to the south of this mount, two
out of the three craters of the Puy de Barme and the Puy de Vichatel are
perfect; but most of the crater-cones south of the Puy de Dome are
breached. Some of the lava streams by which these craters were broken
down flowed for long distances. That the lava followed the showers of
ashes and lapilli forming the walls of the craters is rendered very
evident in the case of the Puy de la Vache, whose lava-stream coalescing
with those from the Puy de la Solas and Puy Noir, deluged the
surrounding tracts and flowed down the Channonat Valley as far as La
Roche Blanc in the Vale of Clermont. In the interior of the upper part
of the crater still remaining may be seen the level (so to speak) to
which the molten lava rose before it burst its barrier. This level is
marked by a projecting platform of reddish or yellow material, rich in
specular iron, apparently part of the frothy scum which formed on the
surface of the lava and adhered to the side of the basin at the moment
of its being emptied.

Space does not permit a fuller description of this remarkable assemblage
of extinct volcanoes, and the re