http://cat.petagonia.com/

Here is something that I just found on the internet.... if I did the link right you can read the whole article but I am gonna paste below the part about clay litter....Clumping clay litter, which forms a hard ball when it gets wet, is one of the most harmful types on the market. Several brands use this clay to make thier litter easier to scoop. What makes it clump? It's a natural clay ingredient called sodium bentonite. In this case, "natural" is not always safe. Here's the problem: When this clay gets wet it expands and forms a hard mass. So when your cat or kitten digs in the litter box it's stirring up clay dust and breathing it in. Once it gets into their lungs, it expands from the moisture, and in time builds up, causing all sorts of lung problems like the ones mentioned above. For the complete kitty litter alert....