overture learning reviews Riddles

Dark with white markings, And smooth like a rock. Where learning occurs, I help convey thought. What am I?

A young boy went to a Catholic school. During school, he started goofing around, so the teacher called him out and sent him to the Pastor. Since this was a traditional school the boy would be spanked, but the Pastor believed in giving people a chance. He said, "If you can ask me a question about something you learned and I don't know the answer on the spot you will go free." The boy may have been lazy, but he was very witty. He asked, "What is it that you can see and I can see, usually every day, but God cannot see." The Pastor stood there, stumped. He couldn't figure it out because he strongly believed that God sees and knows all, and that there is only one God. The boy smiled and told him. What was it?