she has a Master over her, whose name--I say again--I leave you to guess.

So now that I have taught you not to be afraid of Madam How, we will go
and watch her at her work; and if we do not understand anything we see,
we will ask her questions. She will always show us one of her lesson
books if we give her time. And if we have to wait some time for her
answer, you need not fear catching cold, though it is November; for she
keeps her lesson books scattered about in strange places, and we may have
to walk up and down that hill more than once before we can make out how
she makes the glen.

Well--how was the glen made? You shall guess it if you like, and I will
guess too. You think, perhaps, that an earthquake opened it?

My dear child, we must look before we guess. Then, after we have looked
a little, and got some grounds for guessing, then we may guess. And you
have no ground for supposing there ever was an earthquake here strong
enough to open that glen. There may have been one: but we must guess
from what we do know, and not from what we do not.

Guess again. Perhaps it was there always, from the beginning of the
world? My dear child, you have no proof of that either. Everything
round you is changing in shape daily and hourly, as you will find out the
longer you live; and therefore it is most reasonable to suppose that this
glen has changed its shape, as everything else on earth has done.
Besides, I told you not that Madam How had made the glen, but that she
was making it, and as yet has only half finished. That is my first
guess; and my next guess is that water is making the glen--water, and
nothing else.