Subject: Which soil is less permeable, sand or clay?

Hello. I apologize for not explaining my previous question more 
specifically. It's just that I'm stuck on a few questions I got from my 
science class. I'm not really sure but I think it means permeable to water.

So if clay-sized particles are smaller than sand sized particles how does 
it make one soil more permeable to water than the other?

Also I'd like to know if you would find different kinds of humus in desert 
soil as compared to a tropical soil.

*Thank you very much and I really appreciate how you
use this valuable time on helping kids like me.*

Re: Which soil is less permeable, sand or clay?