Have you tried moving the end node of the cave wall section, and while moving it using F9 to snap to the closest node/point on the corridor end?

Or, if you have any experience with the trim tools in the Edit menu, you could try hiding all but the wall sheet(s) and use the tools to trim the ends to each other. Instructions are given in the command line depending on which tool you use.

Is this better?

When the ocean was dark the ice looked white, even though it was blue.

I forgot to thank you, Jack. Thank you :)

Thanks :)

I've adjusted the badland fills. The backgrounds now all match, but I'm a little unsure of the patch colours.

I alreaday have marsh and swamp fills done in a similar way, but I think they might need updating. I have modified the colour of the water textures since doing them.

Ice floes, though, are currently being done as polygons of the Ice texture. Maybe I should make an ice flow fill...