World Spawn Layer under current Layer

I have the following script spawning my parts of my world. I would like to add another layer to this shape just bellow the current one just not sure how to do it. Here is my script so far.

using UnityEngine;
using System.Collections;

public class WorldSpawn : MonoBehaviour {


public GameObject block1; 
int worldWidth  = 6;
int worldHeight  = 6;
float spawnSpeed = 0;
 
void  Start ()
	{
StartCoroutine(CreateWorld());
}
 
IEnumerator CreateWorld (){
 
    for(int x =0; x<worldWidth; x+=1) {
      yield return new WaitForSeconds(spawnSpeed);
     for(int z =0; z<worldHeight; z+=1) {
      yield return new WaitForSeconds(spawnSpeed);
 
      GameObject block = Instantiate(block1,block1.transform.position, block1.transform.rotation)as GameObject;
 
      block.transform.localPosition = new Vector3(x, 0, z);
 
      }
 
      }
 
      }
}

It seems like you need a ‘worldDepth’ variable and the nesting of another for loop.

for (x)
    for (z)
        for (y)
            // instantiate blocks