t abreast of it! No prominent hill would stick to its shape long
enough for me to make up my mind what its form really was, but it was as
dissolving and changeful as if it had been a mountain of butter in the
hottest corner of the tropics. Nothing ever had the same shape when
I was coming downstream that it had borne when I went up. I mentioned
these little difficulties to Mr. Bixby. He said--

'That's the very main virtue of the thing. If the shapes didn't change
every three seconds they wouldn't be of any use. Take this place where
we are now, for instance. As long as that hill over yonder is only one
hill, I can boom right along the way I'm going; but the moment it splits
at the top and forms a V, I know I've got to scratch to starboard in a
hurry, or I'll bang this boat's brains out against a rock; and then the
moment one of the prongs of the V swings behind the other, I've got to
waltz to larboard again, or I'll have a misunderstanding with a snag
that would snatch the keelson out of this steamboat as neatly as if it
were a sliver in your hand. If that hill didn't change its shape on bad
nights there would be an awful steamboat grave-yard around here inside
of a year.'

It was plain that I had got to learn the shape of the river in all the
different ways that could be thought of,--upside down, wrong end first,
inside out, fore-and-aft, and 'thortships,'--and then know what to do on
gray nights when it hadn't any shape at all. So I set about it. In the
course of time I began to get the best of this knotty lesson, and my
self-complacency moved to the front once more. Mr. Bixby was all fixed,
and ready to start it to the rear again. He opened on me after this
fashion--

'How much water did we have in the middle crossing at Hole-in-the-Wall,
trip before last?'

I considered this an outrage. I said--

'Every trip, down and up, the leadsmen are singing through that tangled
place for three-quarters of an hour on a stretch. How do you reckon I
can remember such a mess as that?'

'My boy, you've got to remember it. You've got to remember the exact
spot and the exact marks the boat lay in when we had the shoalest water,
in everyone of the five hundred shoal places between St. Louis and New
Orleans; and you mustn't get the shoal soundings and marks of one trip
mixed up with the shoal soundings and marks of another, either, for
they're not often twice alike. You must keep them separate.'

When I came to myself again, I