along such fissures; he showed how the most remarkable plateaux, composed
of successive lava sheets, might be built up by repeated and moderate
ejections from numerous isolated vents; and he expressly insists upon the
rapidity with which the cinder-cones around the orifices of ejection and
the evidences of successive outflows of lava would be obliterated by
denudation.

One of the most striking parts of the book is that in which he deals with
the effects of denudation in producing "basal wrecks" or worn down stumps
of volcanoes. He was enabled to examine a series of cases in which could be
traced every gradation, from perfect volcanic cones down to the solidified
plugs which had consolidated in the vents from which ejections had taken
place. Darwin's observations on these points have been of the greatest
value and assistance to all who have essayed to study the effects of
volcanic action during earlier periods of the earth's history. Like Lyell,
he was firmly persuaded of the continuity of geological history, and ever
delighted in finding indications, in the present order of nature, that the
phenomena of the past could be accounted for by means of causes which are
still in operation. Lyell's last work in the field was carried on about his
home in Forfarshire, and only a few months before his death he wrote to
Darwin: "All the work which I have done has confirmed me in the belief that
the only difference between Palaeozoic and recent volcanic rocks is no more
than we must allow for, by the enormous time to which the products of the
oldest volcanoes have been subjected to chemical changes."

Darwin was greatly impressed, as the result of his studies of volcanic
phenomena, followed by an examination of the great granite-masses of the
Andes, with the relations between the so-called Plutonic rocks and those of
undoubtedly volcanic origin. It was indeed a fortunate circumstance, that
after studying some excellent examples of recent volcanic rocks, he