What's all this?

OK, so this morning I was doing laundry from our little trip. While the washing machine was filling up with water I was throwing in jeans, jackets etc. As I was tossing a pair of Joshua's pants into the machine, with the pockets facing down, I heard a big clunk. Then I heard several smaller clunks. I quickly retrieved these pants from the washer and I felt inside the pockets.

There I pulled out three handfuls of rocks. I let out a little grumble and quickly turned off the water. Then I had to dig through the clothes and through the water to find all the other rocks that had already fallen out. Here is what I found. I knew Joshua had picked up three or four rocks because he started crying when he thought he had lost one, but seriously, I had no idea about all these other rocks. Several of them are big too. What is the child thinking? I know rocks are cool and all, but this is a bit much.