Geology Reference
In-Depth Information
Map of Siccar Point, Scotland, showing its position on the coast east of Edinburgh.
At the bottom lay a jewel of an outcrop. The two rock formations sat there just as text-
books showed. Here, in front of me, were the rocks that helped inspire geology's core
concept of deep time, that the world is billions of years old. Over lunch I read the story in
the rocks, laid out plain as day.
The older gray sandstone formed as debris eroded off an ancient upland and settled to
the bed of an adjacent sea until the sand eventually lay buried deep enough that heat and
pressure turned it into solid rock. Then, something caused the rocks to buckle, lifting them
back above sea level and tipping them into their now vertical orientation. Gazing along the
shore, I could see how the contact between the two sandstones defined the surface of an
ancient valley carved into the gray sandstone. As this new land sank back down beneath
the waves of an ancient sea, red sand settled on top, eventually accumulating into enough
of a pile to turn it, too, into bona fide rock. After all that, another round of tilting and uplift
brought the works back to the surface, where waves peeled the cliff back to expose a low
