Where the Bus Stopped

Originally published as a school reader, this book is a very difficult title to find. Michael and Mary are given some money and decide to take a mystery trip to a destination that they see on the front of a bus. The conductor is interested in birds and directs them to a quarry, where they can do some birdwatching. When they get there they help to protect the eggs of some rare birds and they rescue a boy who falls over a cliff.