Moon rock in the High Peaks

Photo by Eric W. Sydor

Whenever I’m stuck for the next book to read, I can always go back to John McPhee, whose crisp sentences go down easily no matter what mood you’re in.

I’ve been rereading his collection Irons in the Fire, and although I never thought McPhee’s volumes on geology were as interesting as his other work, his long essay “The Gravel Page,” about the use of forensic geology to catch criminals, is fascinating. It’s peppered with quotations from Sherlock Holmes (the phrase “the gravel page” is from Conan Doyle) and it gave me a startling new viewpoint on the gray rock of the Adirondack High Peaks, which I used to scramble around during my high school days in Lake Placid.

Here ... were a dozen pebbles of anorthosite—looking like blue cheese with their gray crystals and yellow weathery rinds—and one could say with certainty just where they came from. There is an anorthosite body of limited dimension in the Laramie Range northeast of Laramie. You would find a very large percentage of pebbles like these in Horse Creek coming out of the Laramies toward the Platte. A monomineralic rock, anorthosite is rare on this planet and very old. Unaccountably, it formed only during the Archean Eon and an era later in the Precambrian known as Neo-Helikian time. Westward, the next anorthosite outcrop would be in the San Gabriel Mountains, above Los Angeles. Eastward, there would be scattered outcroppings in the Canadian Shield. Anorthosite, in unearthly proportions, is the rock of all the high Adirondacks. Upward, it is plentiful in the night sky, being most of what you are looking at when you look at the moon.