Terrain Generator

Terrain Generators control the overall shape of a Age. Exactly one terrain generator must appear in an age description. Except for Void World, each option takes two material modifiers, for the land and sea materials. These default to stone and (usually) water, but if not specified, something else may well be chosen. However, they are restricted to "appropriate blocks":
 * For the solid terrain, dirt and most "natural" stone-type blocks qualify, as does packed ice. Wood, brick and ore blocks do not qualify.
 * If the terrain material is not stone, most ore placement will not happen, though stone tendrils and such can still get ore. Exception: netherrack will get nether quartz ore.
 * Similarly, if the terrain is not stone, the surface will not get the "biome replacement" that normally provides dirt, sand, gravel, etc. Again, tendrils and such in the proper height range can get replacement.
 * If the terrain is not stone (with biome replacement) or dirt, most plants and trees will not be placed.
 * For the ocean terrain, options are more limited: Water, lava, black ink, ice or packed ice can be used, as can many mod liquids.  The special symbol No Seas (effectively, air) can also be used, and is the default for Island or Void worlds.
 * Some mod liquids are "seabanned" for various reasons. Others are considered valuable enough that a sea of those will produce extreme instability.
 * Note that seas are not placed as a modification to the terrain -- rather, the sea block is used to fill any areas below sea level (Y=63). If a world is entirely above sea level (all high biomes, or a flatland above sea level), there will be no oceans.

The choices for a Terrain Generator are as follows:
 * Standard Terrain: A landscape similar to the normal Overworld.
 * Amplified Normal Terrain: Exaggerated heights and valleys, similar to the "Amplified" option available for Overworld creation.
 * Cave World: An enclosed world similar to the Nether.
 * Note that there is a flat top layer, and if the original spawn point is blocked, the player can appear there.
 * For most of version 0.11, the Cave World symbol automatically added some instability, to reflect easier access to ore. This was removed in V0.11.13, as the new profiling system was able to detect and account for ore accessibility directly.
 * The increased accessibility will generally produce 2-3 "surface" effects in an otherwise normal overworld clone. Being inside the cave will generally be safe. However, "surface" effects can include mob regeneration and mob resistance, both of which will affect all mobs underground.
 * Cave worlds will be dark. The nether's dim background lighting that lets you see will not be present. Bright Lighting can remedy that at the cost of more instability.
 * Island World: A large floating island similar to the End.  Island worlds default to No Seas.
 * Void World: No terrain is generated at all, though some features such as Tendrils or Floating Islands can still appear.  Void World does not need or accept any material (or other) modifiers.