THE ANCIENT VOLCANOES OF GREA T BRITAIN 
viii 
of Central France were not all of one age, but had made their appearance in 
a long series, whereof the individual ineinhers became less perfect and distinct 
in proportion to their antiquity. Beginning with the cones, craters, and 
lava-streams which stand out so fresh that they might almost be supposed 
to have been erupted only a few generations ago, Desuiarest traced the 
volcanic series backward in time, through successive stages of the decay and 
degradation wrought upon them by the iiiilueuee of the atmosphere, rain 
and running water. He was thus able, as it were, to watch the gradual 
obliteration of the cones, tlie removal of the ashes and scoripe, and the 
erosion of the lava-streams, until lie could point to mere isolated remnants 
of lava, perched upon the hills, and overlooking the valleys which had been 
excavated through them. He showed how every step in this process of 
denudation could be illustrated by examples of its occurrence in Auvergne, 
and how, in this way, the various eruptions coidd be grouped according to 
their place in the chronological sequence. To this illustrious Frenchman 
geology is thus indebted, not only for the foundation of the scientific study 
of former volcanic action, but for the first carefully worked out example of 
the potency of subairial erosion in the excavation of valleys and tlie trans- 
formation of the scenery of the land. 
While these fruitful researches were in progress in France, others of 
hardly less moment were advancing in Scotland. There liiiewise Nature had 
provided ample material to arrest the attention of all who cared to make 
themselves acquainted with the past history of our globe. Hutton, as a 
part of his immortal Theory of the Earth, had conceived the idea that 
much molten material had been injected from below into the terrestrial 
crust, and he had found many proofs of such intrusion among the rocks 
alike of the Lowlands and Highlands of his native country. His observa- 
tions, eonfiriued and extended by Playfair and Hall, and subsequently by 
Macculloch, opened up the investigation of the subterranean phases of 
ancient volcanic action. 
Under the influence of these great pioneers, volcanic geology would have 
made steady and perhaps rapid progress in the later decades of last century, 
and the earlier years of the present, but for the theoretical views unfortunately 
adopted by Werner. That illustrious teacher, to whom volcanoes seemed to 
be a blot on the system of nature which he had devised, did all in his 
power to depreciate tlieir importance. Adopting the old and absurd notion 
that they were caused by the combustion of coal under ground, he laboured 
to show that they were mere modern accidents, and had no connection with 
his universal formations. He proclaimed, as an obvious axiom in science, 
that the basalts, so widely spread over Central and Western Europe, and 
which the observations of Desmarest had shown to mark the sites of old 
