of superposition of certain mineral groups; but he had been
anticipated, as has been shown in the last chapter, in the discovery of
this general law, by several geologists in Italy and elsewhere; and his
leading divisions of the secondary strata were at the same time, and
independently, made the basis of an arrangement of the British strata by
our countryman, William Smith, to whose work I shall refer in the
sequel.

_Controversy between the Vulcanists and Neptunists._--In regard to
basalt and other igneous rocks, Werner's theory was original, but it was
also extremely erroneous. The basalts of Saxony and Hesse, to which his
observations were chiefly confined, consisted of tabular masses capping
the hills, and not connected with the levels of existing valleys, like
many in Auvergne and the Vivarais. These basalts, and all other rocks of
the same family in other countries, were, according to him, chemical
precipitates from water. He denied that they were the products of
submarine volcanoes; and even taught that, in the primeval ages of the
world, there were no volcanoes. His theory was opposed, in a twofold
sense, to the doctrine of the permanent agency of the same causes in
nature; for not only did he introduce, without scruple, many imaginary
causes supposed to have once effected great revolutions in the earth,
and then to have become extinct, but new ones also were feigned to have
come into play in modern times; and, above all, that most violent
instrument of change, the agency of subterranean heat.

So early as 1768, before Werner had commenced his mineralogical studies,
Raspe had truly characterized the basalts of Hesse as of igneous origin.
Arduino, we have seen, had pointed out numerous varieties of trap-rock
in the Vicentin as analogous to volcanic products, and as distinctly
referable to ancient submarine eruptions. Desmarest, as before stated,
had, in company with Fortis, examined the Vicentin in 1766, and
confirmed Arduino's views. In 1772, Banks, Solander, and Troil compared
the columnar basalt of Hecla with that of the Hebrides. Collini, in
1774, recognized the true nature of the igneous rocks on the Rhine,
between Andernach and Bonn. In 1775, Guettard visited the Vivarais, and
established the relation of basaltic currents to lavas. Lastly, in 1779,
Faujas published his description of the volcanoes of the Vivarais and
Velay, and showed how the streams of basalt had poured out from craters
which still remai