“Rocks have stories,” geologist Marcia Bjornerud says in this week’s episode of our series on Deep Time, “How Earth Keeps Time.” Then she tells me about rock hunting in Wisconsin’s Baraboo hills and her irresistible attraction to purple Baraboo quartzite, which she describes as “almost sensuous in nature.” I know next to nothing about rocks but they have a similar lure for me and I’ve been pocketing them for years: smooth black pebbles from Lake Michigan beaches; red rocks from Ozark creek beds and speckled stone eggs from the shores of Cape Cod. I pick up stones out of some kind of totemic instinct – for the way a single lump of basalt on a dresser can represent an entire landscape. A rock can be a spell to bind memories of a beloved place or person. But I’m ashamed to say that it hadn’t occurred to me to be curious about their own stony histories or to appreciate the long independent lives they led before being plucked from their natural surroundings.
Oh, what I’ve been missing. On the mantel above the fireplace in the house where I’m staying are two rocks – dark gray, ribboned with lines of white. Moody, evocative and a little magical, I’ve admired them for years. Steve’s parents probably picked them up years ago while hiking or picnicking somewhere in New England, but it didn’t take much digging for me to discover that they’re wonderful examples of Vermont “linestones” – aka Iberville shale. Five hundred million years ago, the place we call Vermont was a tropical ocean. Calcium carbonate floated in the water, contributing building material for coral and shells. Meanwhile, silt deposits settled on the ocean floor, hardening, slowly, into shale. Over millions of years, sea creatures came and went, and their bodies dissolved, releasing calcium, which made its way into cracks and folds in the shale created by seismic activity. At least, that’s my rough understanding of the process that produced the iconic stones found on Lake Champlain’s rocky shores. That two of them traveled so far to sit quietly in my living room today seems almost too miraculous to grasp.
Deep time is all around us, if we know where – and how – to look!
– Anne