On Day 18 of our trek across the USA, we visited Petrified Forest National Park. Tree trunks made of rock! Now what do you make of that? And what are these tall trees doing here in the desert and why aren’t they growing here now? Answers to those questions involve many millions of years and an understanding of the earth as a changing place and an understanding that rock is not as permanent and immovable as it appears. “I am a rock!” sang Simon and Garfunkle decades ago, a metaphor for someone who doesn’t change. It may not be that good a metaphor for what is unchanging.
