Good idea extending the cliff and the coal mine came out great, don't be afraid to weather it up and just keep in mind dirt flows downward. If you don't mind I'd like to make a suggestion with the rockwork, if you get some matte medium( I make my own ) and give your rock outcrops a spray with the matte medium and get something like the woodland scenic earth its very fine or even something like baseball diamond dirt sifter through a panty hose then put on a sheet of paper and just give the dirt a light blow onto the rock faces here and there while its wet and you would not believe the effect it has on the rocks. Can do the same with fine ws leaves, after all moss does grow on the rocks.