To gauge a writer, one might consider his or her ability to transform something ostensibly banal, like chalk, ordinary blackboard chalk, ordinary calcium carbonate, ordinary grape-growing stuff, into something interesting. Unsurprisingly, to read John McPhee’s most recent collection of essays, Silk Parachute, is to marvel at the way he elicits a temperament the opposite of boredom. “Season on the Chalk” begins on the River Thames at Gravesend, with McPhee’s grandson, Tommaso, appearing “out of somewhere” with a broken river stone and writing one letter on the revetment: R. A revetment is a barricade. “Somewhere” is McPhee, and more generally, any author.