Local pebbles for my automata

Here's a selection of pebbles I've been collecting over the last few weeks from my local beach.
I use them as counterweights or ballast for my automata. They allow me to minimize the use of springs and give my automata a local flavor.
I used a pebble as a counterweight in Laughing Machine #1.
The ones with holes are particularly precious because they're easy to mechanically attach to cam followers, etc. 
What can you find in your area to incorporate in your automata?