[1.7.10] Issue with theBiomeDecorator

Dear all

I've recently started to tinker around with custom biomes and their decoration.

But now I am slightly confused, with theBiomeDecorator object.

In the constructor of my custom biome I use the following code to get only a few trees:

this.theBiomeDecorator.treesPerChunk = 1;

Which works absolutely fine.

Then again, the follwing snipped seems not to work:

this.theBiomeDecorator.sandGen = new WorldGenSand(Blocks.clay, 7);//7 just like vanilla

May someone knows why this doesn't work while changing the amount of trees per chunk does?

The final target is to replace the vanilla sand/gravel near lakes with my custom block, may I am at the wrong place to achieve it?

Thanks in advance for any responses!

Sincerely -pick