diff --git a/src/java/mmm/materials/MQuicksand.java b/src/java/mmm/materials/MQuicksand.java
index 837d200..5ade103 100644
--- a/src/java/mmm/materials/MQuicksand.java
+++ b/src/java/mmm/materials/MQuicksand.java
@@ -1,6 +1,7 @@
 package mmm.materials;
 
 
+import mmm.utils.I_UTrapBlock;
 import mmm.utils.URegistry;
 import net.minecraft.block.Block;
 import net.minecraft.block.BlockFalling;
@@ -21,6 +22,7 @@ import net.minecraftforge.common.IPlantable;
 
 public class MQuicksand
 		extends BlockFalling
+		implements I_UTrapBlock
 {
 	public final IBlockState forType;
 
@@ -36,6 +38,13 @@ public class MQuicksand
 	}
 
 
+	@Override
+	public IBlockState getReplacedBlock( )
+	{
+		return this.forType;
+	}
+
+
 	@Override
 	public MapColor getMapColor( IBlockState state )
 	{
diff --git a/src/java/mmm/utils/I_UTrapBlock.java b/src/java/mmm/utils/I_UTrapBlock.java
new file mode 100644
index 0000000..a7c2d4b
--- /dev/null
+++ b/src/java/mmm/utils/I_UTrapBlock.java
@@ -0,0 +1,13 @@
+package mmm.utils;
+
+
+import net.minecraft.block.state.IBlockState;
+
+
+
+public interface I_UTrapBlock
+{
+
+	public IBlockState getReplacedBlock( );
+
+}
diff --git a/src/java/mmm/utils/URegistry.java b/src/java/mmm/utils/URegistry.java
index 062157e..c0a4a06 100644
--- a/src/java/mmm/utils/URegistry.java
+++ b/src/java/mmm/utils/URegistry.java
@@ -156,6 +156,9 @@ public class URegistry
 
 			URegistry.addRecipeRegistrar( block );
 			URegistry.addOreGenerationRegistrar( block );
+			if ( block instanceof I_UTrapBlock ) {
+				UTrapBlocks.INSTANCE.register( (I_UTrapBlock) block );
+			}
 
 			if ( blockItem != null ) {
 				URegistry.addItem( blockItem , registerItemModel );
diff --git a/src/java/mmm/utils/UTrapBlocks.java b/src/java/mmm/utils/UTrapBlocks.java
new file mode 100644
index 0000000..bbb71cd
--- /dev/null
+++ b/src/java/mmm/utils/UTrapBlocks.java
@@ -0,0 +1,30 @@
+package mmm.utils;
+
+
+import java.util.List;
+
+import com.google.common.collect.ArrayListMultimap;
+
+import net.minecraft.block.Block;
+import net.minecraft.block.state.IBlockState;
+
+
+
+public enum UTrapBlocks {
+	INSTANCE;
+
+	private final ArrayListMultimap< IBlockState , IBlockState > replacements = ArrayListMultimap.create( );
+
+
+	public void register( final I_UTrapBlock block )
+	{
+		this.replacements.put( block.getReplacedBlock( ) , ( (Block) block ).getDefaultState( ) );
+	}
+
+
+	public List< IBlockState > getReplacements( final IBlockState blockState )
+	{
+		return this.replacements.get( blockState );
+	}
+
+}
diff --git a/src/java/mmm/world/WDefaultGenWatcher.java b/src/java/mmm/world/WDefaultGenWatcher.java
index 39cf69c..465633e 100644
--- a/src/java/mmm/world/WDefaultGenWatcher.java
+++ b/src/java/mmm/world/WDefaultGenWatcher.java
@@ -1,8 +1,12 @@
 package mmm.world;
 
 
+import mmm.world.biome.I_WBTrappedBiome;
+import mmm.world.gen.WGTrapBlocks;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.biome.Biome;
+import net.minecraft.world.biome.BiomeDesert;
+import net.minecraft.world.biome.BiomeSwamp;
 import net.minecraftforge.event.terraingen.PopulateChunkEvent;
 import net.minecraftforge.fml.common.eventhandler.Event.Result;
 import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
@@ -23,4 +27,31 @@ public class WDefaultGenWatcher
 		}
 	}
 
+
+	@SubscribeEvent
+	public void afterPopulate( final PopulateChunkEvent.Post event )
+	{
+		if ( event.isHasVillageGenerated( ) ) {
+			return;
+		}
+
+		final BlockPos bp = new BlockPos( event.getChunkX( ) * 16 , 0 , event.getChunkZ( ) * 16 );
+		final net.minecraft.world.World world = event.getWorld( );
+		final Biome biome = world.getBiomeGenForCoords( bp );
+		// FIXME hardcoding is bad
+
+		final WGTrapBlocks traps;
+		if ( biome instanceof BiomeDesert ) {
+			traps = new WGTrapBlocks( false , .05f );
+		} else if ( biome instanceof BiomeSwamp ) {
+			traps = new WGTrapBlocks( false , .1f );
+		} else if ( biome instanceof I_WBTrappedBiome ) {
+			traps = new WGTrapBlocks( false , ( (I_WBTrappedBiome) biome ).getTrapBlockChance( ) );
+		} else {
+			return;
+		}
+
+		traps.generate( world , event.getRand( ) , bp );
+	}
+
 }
diff --git a/src/java/mmm/world/World.java b/src/java/mmm/world/World.java
index d45bff6..d914af3 100644
--- a/src/java/mmm/world/World.java
+++ b/src/java/mmm/world/World.java
@@ -21,7 +21,10 @@ public class World
 {
 
 	static {
-		MinecraftForge.TERRAIN_GEN_BUS.register( new WDefaultGenWatcher( ) );
+		WDefaultGenWatcher dgw = new WDefaultGenWatcher( );
+		MinecraftForge.TERRAIN_GEN_BUS.register( dgw );
+		MinecraftForge.EVENT_BUS.register( dgw );
+
 		WBiomeHelper helper;
 
 		helper = new WBiomeHelper( WBLimestoneMountains::new );
@@ -71,7 +74,7 @@ public class World
 				.setElevation( -.2f , .1f ) //
 				.setWeather( .95f , .95f ) //
 				.setWaterColor( 0xe0ffae ) // Same as vanilla swamps
-				.setType( BiomeType.WARM , 40 ) // FIXME
+				.setType( BiomeType.WARM , 3 ) //
 				.register( );
 	}
 
diff --git a/src/java/mmm/world/biome/I_WBTrappedBiome.java b/src/java/mmm/world/biome/I_WBTrappedBiome.java
new file mode 100644
index 0000000..ccd86ca
--- /dev/null
+++ b/src/java/mmm/world/biome/I_WBTrappedBiome.java
@@ -0,0 +1,7 @@
+package mmm.world.biome;
+
+
+public interface I_WBTrappedBiome
+{
+	public float getTrapBlockChance( );
+}
diff --git a/src/java/mmm/world/gen/WGTrapBlocks.java b/src/java/mmm/world/gen/WGTrapBlocks.java
new file mode 100644
index 0000000..805d1c1
--- /dev/null
+++ b/src/java/mmm/world/gen/WGTrapBlocks.java
@@ -0,0 +1,100 @@
+package mmm.world.gen;
+
+
+import java.util.List;
+import java.util.Random;
+
+import mmm.utils.UTrapBlocks;
+import net.minecraft.block.material.Material;
+import net.minecraft.block.state.IBlockState;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.World;
+import net.minecraft.world.gen.feature.WorldGenerator;
+
+
+
+public class WGTrapBlocks
+		extends WorldGenerator
+{
+
+	private final float chance;
+
+
+	public WGTrapBlocks( final boolean notify , final float chance )
+	{
+		super( notify );
+		this.chance = chance;
+	}
+
+
+	@Override
+	public boolean generate( final World worldIn , final Random rand , final BlockPos position )
+	{
+		if ( rand.nextFloat( ) > this.chance ) {
+			return false;
+		}
+
+		// Select radius and centre
+		final int radius = 2 + rand.nextInt( 2 );
+		final int space = 16 - radius * 2;
+		final BlockPos.MutableBlockPos check = new BlockPos.MutableBlockPos(
+				position.getX( ) + radius + rand.nextInt( space ) , //
+				255 , //
+				position.getZ( ) + radius + rand.nextInt( space ) );
+
+		// Find the ground
+		final int minDepth = Math.max( 0 , worldIn.getSeaLevel( ) - 20 );
+		boolean found = false;
+		while ( check.getY( ) > minDepth ) {
+			final Material material = worldIn.getBlockState( check ).getMaterial( );
+			if ( material.isLiquid( ) ) {
+				return false;
+			}
+			if ( material != Material.AIR ) {
+				found = true;
+				break;
+			}
+			check.setY( check.getY( ) - 1 );
+		}
+		if ( !found ) {
+			return false;
+		}
+
+		// Displace the centre vertically
+		if ( check.getY( ) > radius / 2 && check.getY( ) < 255 - radius / 2 ) {
+			check.setY( check.getY( ) - radius / 2 + rand.nextInt( radius ) );
+		}
+
+		// Replace blocks
+		BlockPos bp = new BlockPos( check );
+		int sqr = radius * radius;
+		for ( int x = -radius ; x <= radius ; x++ ) {
+			for ( int y = -radius ; y <= radius ; y++ ) {
+				for ( int z = -radius ; z <= radius ; z++ ) {
+					if ( x * x + y * y + z * z > sqr + rand.nextInt( 2 ) ) {
+						continue;
+					}
+
+					final BlockPos pos = bp.add( x , y , z );
+					final IBlockState atPos = worldIn.getBlockState( pos );
+					final List< IBlockState > replacements = UTrapBlocks.INSTANCE.getReplacements( atPos );
+					final int nReplacements = replacements.size( );
+					if ( nReplacements == 0 ) {
+						continue;
+					}
+
+					int repIndex;
+					if ( nReplacements == 1 ) {
+						repIndex = 0;
+					} else {
+						repIndex = rand.nextInt( nReplacements );
+					}
+					this.setBlockAndNotifyAdequately( worldIn , pos , replacements.get( repIndex ) );
+				}
+			}
+		}
+
+		return true;
+	}
+
+}