What are these things in Labyrinth Zone?

[Jonny Axehandle]

The cork-looking floating things with all the holes. When I was a kid I thought they were cheese. Are they supposed to be pumice rocks?

 

[GavinMcWario]

Maybe they really are just really big corks? The shading compared to the other blocks kinda implies to me that they're supposed to be cylinders, not blocks.