Thanks, chaps....I think....

And my geomorphology ends here, because I would not know how to bring these two formations together 
That is all I am aiming for: To get the different rocks to look 'right' together, hence the unifying colour scheme.
I am really not that bothered about gettings things correct, just so as they look ok when they are all on the table together.

Was the very big one the one you had to fill? If not (because I can't be bothered with all that) where did you find it?
Everything is nice btw (goes without saying, not going to repeat myself).
It was the small one that I had to fill, a;though it wasn't any bother.
I just shoved the blue foam in the hole and plugged with green stuff and milliput.
About ten minutes work.
Most of that time was used up mixing the two parts of the putty together.

Both of the aquarium rocks, and ones in the previous post, are from ebay.
I shall send you the link, they have quite a selection.
