gravel-beds belong in fact to the glacial period, and in after
years I found in them broken arctic shells. But I was then
utterly astonished at Sedgwick not being delighted at so
wonderful a fact as a tropical shell being found near the surface
in the middle of England. Nothing before had ever made me
thoroughly realise, though I had read various scientific books,
that science consists in grouping facts so that general laws or
conclusions may be drawn from them.

Next morning we started for Llangollen, Conway, Bangor, and Capel
Curig. This tour was of decided use in teaching me a little how
to make out the geology of a country. Sedgwick often sent me on
a line parallel to his, telling me to bring back specimens of the
rocks and to mark the stratification on a map. I have little
doubt that he did this for my good, as I was too ignorant to have
aided him. On this tour I had a striking instance of how easy it
is to overlook phenomena, however conspicuous, before they have
been observed by any one. We spent many hours in Cwm Idwal,
examining all the rocks with extreme care, as Sedgwick was
anxious to find fossils in them; but neither of us saw a trace of
the wonderful glacial phenomena all around us; we did not notice
the plainly scored rocks, the perched boulders, the lateral and
terminal moraines. Yet these phenomena are so conspicuous that,
as I declared in a paper published many years afterwards in the
'Philosophical Magazine' ('Philosophical Magazine,' 1842.), a
house burnt down by fire did not tell its story more plainly than
did this valley. If it had still been filled by a glacier, the
phenomena would have been less distinct than they now are.

At Capel Curig I left Sedgwick and went in a straight line by