n in a perfect state.[99]

_Desmarest._--When sound opinions had thus for twenty years prevailed in
Europe concerning the true nature of the ancient trap-rocks, Werner by
his simple dictum caused a retrograde movement, and not only overturned
the true theory, but substituted for it one of the most unphilosophical
that can well be imagined. The continued ascendancy of his dogmas on
this subject was the more astonishing, because a variety of new and
striking facts were daily accumulated in favor of the correct opinions
previously entertained. Desmarest, after a careful examination of
Auvergne, pointed out, first, the most recent volcanoes which had their
craters still entire, and their streams of lava conforming to the level
of the present river-courses. He then showed that there were others of
an intermediate epoch, whose craters were nearly effaced, and whose
lavas were less intimately connected with the present valleys; and,
lastly, that there were volcanic rocks, still more ancient, without any
discernible craters or scoriae, and bearing the closest analogy to rocks
in other parts of Europe, the igneous origin of which was denied by the
school of Freyberg.[100]

Desmarest's map of Auvergne was a work of uncommon merit. He first made
a trigonometrical survey of the district, and delineated its physical
geography with minute accuracy and admirable graphic power. He
contrived, at the same time, to express without the aid of colors, many
geological details, including the different ages and sometimes even the
structure, of the volcanic rocks, and distinguishing them from the
fresh-water and the granitic. They alone who have carefully studied
Auvergne, and traced the different lava streams from their craters to
their termination,--the various isolated basaltic cappings,--the
relation of some lavas to the present valleys,---the absence of such
relations in others,--can appreciate the extraordinary fidelity of this
elaborate work. No other district of equal dimensions in Europe
exhibits, perhaps, so beautiful and varied a series of phenomena; and,
fortunately, Desmarest possessed at once the mathematical knowledge
required for the construction of a map, skill in mineralogy, and a power
of original generalization.

_Dolomieu--Montlosier._--Dolomieu, another of Werner's contemporaries,
had found prismatic basalt among the ancient lavas of Etna; and, in
1784, had observed the alternations of submarine lavas and calcareous
str