This, I may say, was the only way of 'going ashore' that he really
liked. We raced off as fast as our clumsy sea-boots would let us, and
followed up the course of our channel to the west, reconnoitring the
road we should have to follow when the tide rose.

'The only way to learn a place like this,' he shouted, 'is to see it
at low water. The banks are dry then, and the channels are plain.
Look at that boom'--he stopped and pointed contemptuously--'it's all
out of place. I suppose the channel's shifted there. It's just at an
important bend too. If you took it as a guide when the water was up
you'd run aground.'

'Which would be very useful,' I observed.

'Oh, hang it!' he laughed, 'we're exploring. I want to be able to run
through this channel without a mistake. We will, next time.' He
stopped, and plied compass and notebook. Then we raced on till the
next halt was called.

'Look,' he said, the channel's getting deeper, it was nearly dry a
moment ago; see the current in it now? That's the flood tide coming
up--from the _west,_ mind you; that is, from the Weser side. That
shows we're past the watershed.'

'Watershed?' I repeated, blankly.

'Yes, that's what I call it. You see, a big sand such as this is like
a range of hills dividing two plains, it's never dead flat though it
looks it; there's always one point, one ridge, rather, where it's