It's a small point, but the back side of the island is too smooth and flat. So next, you will add a few contours to make it look more realistic, using the following steps:
Select Layer 2, and then select Layer 1 while holding the Shift key.
Select the island with the RMB. Press the Tab key to go into Edit Mode.
In the 3D View header, choose the Vertex Select mode.
Press A to deselect all of the vertices.
Select a vertex in the center of the cove with the RMB.
Press Shift + S and choose Cursor to Selected from the menu.
In the 3D View header, set Pivot Point to 3D Cursor.
Press 7 on the NumPad. Press the Home key on your keyboard to see the entire island. This is not the Home key on your NumPad. If you are using a Mac, press fn + the left arrow key. Then, use Ctrl + MMB to zoom in.
The bottom and right sides of the island are unnaturally smooth. You need to put in some small variations to make them look right.
Press C and select some...