Now using the Magic Wand Tool, (making sure Sample Merged is Checked and the Threshold is 0) click anywhere in the dark area. This will define your coast. If you want to adjust it, just undo the selection (ctrl-Z) and change the levels of the “Land Clip” layer. I wand back and tightened the coast a bit.
Click image for larger version Name: Post4-2.png Views: 209 Size: 329.4 KB ID: 1430
Now Invert the selection (Select->Invert), create a new black layer called “Land Mask” and fill the selection with white.
Now save the selection to a Channel (Select->Save to Channel) and rename the channel to “Land Mask”. This will be used a bit later.
Click image for larger version Name: Post4-3.png Views: 174 Size: 246.8 KB ID: 1431
Now clear the selection (Select->None).
That technique (the Three-Layer-Sandwich of noise, shape and threshold clip layer, or TLS for short ) will be a basic technique that will be used over and over again, using different blending modes between the noise layer (to give some variegation to the surface) and the shape definition layer. It will be used to define forests and mountains, even clouds in the sky.