lling the rule
laid down (I think by Professor Geikie in his delightful book on
Scotch scenery as influenced by its geology), that ice planes down
into flats, while water saws out into crags and gullies; and that the
rain and frost are even now restoring Scotch scenery to something of
that ruggedness and picturesqueness which it must have lost when it
lay, like Greenland, under the indiscriminating grinding of a heavy
sheet of ice.

Lastly; no known agent, save ice, will explain those perched
boulders, composed of ancient hard rocks, which may be seen in so
many parts of these islands and of the Continent. No water power
could have lifted those stones, and tossed them up high and dry on
mountain ridges and promontories, upon rocks of a totally different
kind. Some of my readers surely recollect Wordsworth's noble lines
about these mysterious wanderers, of which he had seen many a one
about his native hills:

As a huge stone is sometimes seen to lie
Couched on the bald top of an eminence,
Wonder to all who do the same espy
By what means it could thither come, and whence;
So that it seems a thing endued with sense:
Like a sea-beast crawled forth, that on a shelf
Of rock or sand reposeth, there to sun itself.

Yes; but the next time you see such a stone, believe that the wonder
has been solved, and found to be, like most wonders in Nature, more
wonderful than we guessed it to be. It is not a sea-beast which has
crawled forth, but an ice-beast which has been left behind; lifted up
thither by the ice, as surely as the famous Pierre-a-bot, forty feet
in diameter, and hundreds of boulders more, almost as large as
cottages, have been carried by ice from the distant Alps right across
the lake of Neufchatel, and stranded on the slopes of the Jura, nine
hundred feet above the lake. {4}

Thus, I think, we have accounted for facts enough to make it probable
that Britain was once covered partly by an ice-sheet, as Greenland is
now, and partly, perhaps, by an icy sea. But, to make assurance more
sure, let us look for new facts, and try whether our ice-dream will
account for them also. Let us investigate our case as a good medical
man does, by "verifying his first induction."

He says: At the first glance, I can see symptoms a, b, c. It is
therefore probable that my patient has got complaint A. But if he
has he ought to have symptom d also. If I find that, my guess will
be yet more pr