As are some of his phrases. Here's one that caused me to pause and reflect during my lunchtime reading. Two small children he said were "caught in the grave immobility of time". Here's the passage with some context:
I wondered if Matthiessen used the phrase in homage to a piece of writing he admired, but I could find nothing among authors who wrote in English. Some further searching turned up one possibility in another language. This was the phrase "immobilité du temps" in Le lys rouge by Anatole France. Matthiessen pairs well with France. Both crafted elegant prose, both attacked the narrow-minded prejudices of their day, and both found success in fiction and non-fiction, literary writing and journalism, short works and long. (I write of Matthiessen in the past tense, but at 81 he's still going strong.)
Their similarities make it possible that Matthiessen was consciously alluding to France's novel in using his arresting phrase. The phrase is not uncommon in French. I suspect, however, (though I'm not at all sure) that in ordinary usage its meaning is generally closer to "stillness of time" than "immobility of time." If I'm right, and France is unusual in employing the latter, then it's possible (barely so I guess) that Matthiessen consciously echoed France in choosing his words.
Here's a bit of the context in Le Lys rouge: "Elle n’osait pas regarder sa montre, de peur d’y voir l’accablante immobilité du temps. Elle se leva, alla à la fenêtre et souleva les rideaux. Une lueur pâle était répandue dans le ciel nuageux. Elle crut que c’était le jour qui commençait à poindre. Elle regarda sa montre. Il était trois heures et demie." -- Le lys rouge by Anatole France (Lévy, 1896).
I'm not sure which I'd prefer — that Matthiessen graciously alluded to the great French author or that the words came to him with no whisper of their heritage.