added strata generation

Minecraft-Classic-map-generation-algorithm.md

@@ -42,6 +42,7 @@ The players is prompted to choose from 3 default sizes; small medium or large. S
 
 Using:
 * heightMap, a 2D array of size width X depth
+* waterLevel, a constant of 32
 * noise1, a combined noise function with two octave noise functions (of octave 8) as input.
 * noise2, a combined noise function with two octave noise functions (of octave 8) as input.
 * noise3, an octave noise function (of octave 6)
@@ -61,11 +62,32 @@ if heightResult < 0 {
     set heightResult to 8/10 its value
 }
 
-heightMap(x,z) is then set to the integer component of heightResult.
+heightMap(x,z) is then set to the integer component of heightResult + waterLevel.
 ```
 
 ## Create strata
-// Todo
+
+Using:
+* blocks, a 3D array of size width x height x depth
+* noise, an octave noise function (of octave 8)
+
+For each column in the x,z plane populate blocks in array with stone-to-dirt and dirt-to-air transitions:
+```
+Let dirtThickness be noise.compute(x,z) / 24 - 4
+Let dirtTransition be heightMap(x,z)
+Let stoneTransition be dirtTransition + dirtThickness
+
+for y in height {
+    Let blockType be AIR
+    if y equals 0 then blockType is LAVA
+    else if y <= stoneTransition then blockType is STONE
+    else if y <= dirtTransition then blockType is DIRT
+
+    set block(x,y,z) to blockType
+}
+```
+By doing so the block array is populated with lava at height 0, stone along with a variable thickness layer of dirt up to the heightMap elevation for that column and then air above.
+
 ## Carve out caves
 // Todo
 ## Create ore veins