s estimated that so far did he himself practise
what he preached, that no less than one fourth of the period of his
active life was spent in travel[45].

The joint excursion of Lyell and Murchison to the Auvergne was destined
to have great influence on the minds of these pioneers in geological
research; both became satisfied from their studies that, with respect to
the excavation of the valleys of the country, Scrope's conclusions were
irresistible; and in a joint memoir this position was stoutly maintained
by them.

It is interesting to notice the impression made by these two great
geologists on one another during this joint expedition.

Murchison wrote that he had seen in Lyell 'the most scrupulous and
minute fidelity of observation combined with close application in the
closet and ceaseless exertion in the field[46].'

But I recollect that Lyell once told me how difficult Murchison found it
to restrain himself from impatience, when his companion's attention was
drawn aside by his entomological ardour. In an early letter, indeed, we
find that Murchison often expressed a wish that Lyell's sisters had been
with them to attend to the insect-collecting and thus leave Lyell free
for geological work[47].

On the other hand, Lyell informed me that Murchison had rendered him a
great service in showing how much a geologist could accomplish by
taking advantage of riding on horseback, and he declared in his letters
that he 'never had a better man to work with than Murchison';
nevertheless he ridiculed his 'keep-moving-go-it-if-it-kills-you' system
as--quoting from the elder Matthews--he called it[48].

On parting from Murchison and his wife, after the Auvergne tour, Lyell
proceeded to Italy and for more than a year he was busy studying the
Tertiary deposits of Lombardy, the Roman states, Naples and Sicily, and
conferring with the Italian geologists and conchologists. Thus it came
about that he was not free to resume the task of seeing the _Principles_
through the press till February 1829.

Immediately after his return to England Lyell was compelled, with the
assistance of his companion Murchison, to defend their conclusions
concerning the excavations of valleys by rivers from a determined attack
of Conybeare, who was backed up by Buckland and Greenough; the old
geologists endeavoured to prove that the river Thames had never had any
part in the work of forming its valley[49]. It is interesting to find
that, on this occasi