Overworld

The Overworld is the dimension in which you begin. The Overworld is very large on all 3 axes, although much smaller on the Y axis. The Overworld exists in multiple layers, as with every dimension.

Layers
Layers are ordered from the highest elevation to the lowest.

The Top
The Top goes anywhere from 640 to 896. Player movement slows down to 70% if their head is at or above 886. Nothing can be built above 895. The Top contains few things, primarily larger versions of the islands that The Late Pause has.

The Late Pause
The Late Pause goes anywhere from 576 to 640. Like the Early Pause, not much is here, although small, scattered, rocky floating islands may be found, albeit rarely. These rocky islands contain some rare ores you can only find higher up.

The Skylands
The Skylands go anywhere from 320 and 576. The environment is very similar to the Overworld, although the foliage is more unusual. No matter what, there is always a large island centered around the origin, similar to the End. The large island does not have any islands close by, but some exploration will uncover the large, sprawling mass of other islands of varying densities. All areas contain various clouds. Special ores may be found here. This part of the Overworld is similar to the Aether, but all of your tools work perfectly fine in the Skylands.

The Early Pause
The Early Pause goes everywhere from 256 and 320. Very, very few things generate here, mostly mountaintops in Amplified worlds.

Overworld
The Overworld layer of the Overworld goes everywhere from 256 and 0. Normal world generation exists within this layer, although Amplified worlds may reach slightly beyond.

The Early Between
The Early Between goes everywhere from 0 and -64. You have to break the Soft Bedrock or find an existing structure through it to access here and anywhere beneath. Here, the rarer ores can be found slightly more often, even Emerald.

Deep Caverns
The Deep Caverns go everywhere from -64 and -320. To get to here, a second layer of Soft Bedrock impedes your progress. The Deep Caverns are a large expanse of open caves, much like the Nether, but filled with very little liquids of any sort, except the rare water lake. Some ores can only be found by digging this deep. There are also strange trees and huge mushrooms down here.

The Late Between
The Late Between goes everywhere from -320 to -384, and is much harder to get to than the Early Between. The impeding bedrock is a mix of both soft and hard variants. Finding a proper way to get through might take a good while. Ores from the Deep Caverns are here.

The Bottom
At the very bottom of the map, from between -384 and -640 is The Bottom. Pieces of soft bedrock between it and the Late Between are very rare. Around -630, lava is impossible to avoid, which continues to the final layer of bedrock, which is purely hard bedrock. However, many ores that not even the Deep Caverns contain can be found here, and are beyond the ores of legend. Soft Bedrock is scattered within the layer itself.

Generation
All of these are subject to change.

The Top
Cobblestone

Iron Ore

Obsidian

The Late Pause
Cobblestone

Iron Ore

Obsidian

The Skylands
Skydirt

Skygrass

Skystone

Cloud

Skywood

Skyleaves

Skysapling

Hovernite Ore

Magicite Ore

The Early Pause
(AMPLIFIED worlds only)

Stone

Grass

Dirt

Gravel

The Overworld
Includes everything that normally generates

Silver Ore

Soft Bedrock

The Early Between
Stone

Dirt

Gravel

Gold Ore

Iron Ore

Coal Ore

Lapis Lazuli Ore

Diamond Ore

Redstone Ore

Emerald Ore

Silver Ore

Deep Caverns
Stone

Dirt

Gravel

Gold Ore

Iron Ore

Obsidian

Diamond Ore

Redstone Ore

Emerald Ore

Mushroom (block)

Mithril Ore

Aurichalcum Ore

Silver Ore

Soft Bedrock

Hard Bedrock

The Late Between
Stone

Dirt

Gravel

Iron Ore

Mithril Ore

Aurichalcum Ore

Soft Bedrock

Hard Bedrock

The Bottom
Stone

Lava

Soft Bedrock

Hard Bedrock

Eternal Ore

Osmium Ore

Adamantium Ore

Mobs
These are subject to change as well.

The Top
TBA

The Late Pause
TBA

The Skylands
TBA

The Early Pause
TBA

The Overworld
All the original mobs, rest are TBA

The Early Between
TBA

Deep Caverns
Pigman

Slime

Skeleton

Giant Lizard

The Late Pause
TBA

The Bottom
Lava Spirit

Magma Cube

The Top
None, yet.

The Late Pause
None, yet

Skylands
Airships

The Early Pause
None, yet

The Overworld
Dungeons

Deep Tunnels

Fruit Trees

The Early Between
None, yet

Deep Caverns
Pigman Village

The Late Pause
None, yet