after years that it "was a great failure
and I am ashamed of it"--yet he retained his interest in the question
ever afterwards, and he says "my error has been a good lesson to me
never to trust in science to the principle of exclusion." ("M.L." II.
pages 171-93.)

Although Darwin had not realised in 1838 that large parts of the British
Islands had been occupied by great glaciers, he had by no means failed
while in South America to recognise the importance of ice-action. His
observations, as recorded in his Journal, on glaciers coming down to
the sea-level, on the west coast of South America, in a latitude
corresponding to a much lower one than that of the British Islands,
profoundly interested geologists; and the same work contains many
valuable notes on the boulders and unstratified beds in South America in
which they were included.

But in 1840 Agassiz read his startling paper on the evidence of the
former existence of glaciers in the British Islands, and this was
followed by Buckland's memoir on the same subject. On April 14, 1841,
Darwin contributed to the Geological Society his important paper "On the
Distribution of Erratic Boulders and the Contemporaneous Unstratified
Deposits of South America", a paper full of suggestiveness for those
studying the glacial deposits of this country. It was published in the
"Transactions" in 1842.

The description of traces of glacial action in North Wales, by Buckland,
appears to have greatly excited the interest of Darwin. With Sedgwick he
had, in 1831, worked at the stratigraphy of that district, but neither
of them had noticed the very interesting surface features. ("L.L." I.
page 58.) Darwin was able to make a journey to North Wales in June,
1842 (alas! it was his last effort in field-geology) and as a result
he published his most able and convincing paper on the subject in the
September number of the "Philosophical Magazine" for 1842. Thus the
mystery of the bell-stone was at last solved and Darwin, writing many
years afterwards, said "I felt the keenest delight when I first read of
the action of icebergs in transporting boulders, and I gloried in the
progress of Geology." ("L.L." I. page 41.) To the "Geographical Journal"
he had sent in 1839 a note "On a Rock seen on an Iceberg in 16 deg S.
Latitude." For the subject of ice-action, indeed, Darwin retained the
greatest interest to the end of his life. ("M.L." II. pages 148-71.)

In 1846, Darwin read two papers to the Geol