Moisture on crawlspace dirt/clay floor
You will need to seal the basement walls and the basement floor to accomplish this. 

I have seen the dirt removed from around the face of the basement walls and then the walls sealed and the dirt returned - generally it is a trenching around the basement wall of the house - but I have only seen them do one wall. 

There is another way to do it that is easier and works from the inside of the house:

how-to-waterproof-basement