Implemented the functionality to pick and drop the Dirt-balls. Also both rocks and dirt-balls can be moved to cover a water hole, so they have their own sprite to show what has blocked it.
The bad news is that iOS 7 is not handling correctly the touch events. The swift downcasting from SKNode to SKSprite node is failing and thus sometimes the dirt-balls are not being able to be dropped.
Other issue is that it may not be completely clear which dirt-balls can be lifted and where they can be dropped. Spend some time designing the icons to avoid that issue: