Basin and Range by John McPhee

Author:John McPhee
Language: eng
Format: epub
Publisher: Farrar, Straus and Giroux
Published: 2011-06-20T16:00:00+00:00

One is tempted to condense time, somewhat glibly—to say, for example, that the faulting which lifted up the mountains of the Basin and Range began “only” eight million years ago. The late Miocene was “a mere” eight million years ago. That the Rocky Mountains were building seventy million years ago and the Appalachians were folding four hundred million years ago does not impose brevity on eight million years. What is to be avoided is an abridgment of deep time in a manner that tends to veil its already obscure dimensions. The periods are so long—the eighty million years of the Cretaceous, the forty-six million years of the Devonian—that each has acquired its own internal time scale, intricately constructed and elaborately named. I will not attempt to reproduce this amazing list but only to suggest its profusion. The stages and ages, as they are called—the subdivisions of all of the epochs and eras—read like a roll call in a district council somewhere in Armenia. Berriasian, Valanginian, Hauterivian, Barremian, Bedoulian, Gargasian, Aptian, Albian, Cenomanian, Turonian, Coniacian, Santonian, Campanian, and Maastrichtian, reading upward, are chambers of Cretaceous time. Actually, the Cretaceous has been cut even finer, with about fifty clear time lines now, subdivisions of the subdivisions of its eighty million years. The Triassic consists of the Scythian, the Anisian, the Ladinian, the Carnian, the Norian, and the Rhaetian, averaging seven million years. What survived the Rhaetian lived on into the Liassic. The Liassic, an epoch, comes just after the Triassic and is the early part of the Jurassic. Kazanian, Couvinean, Kopaninian, Kimmeridgian, Tremadocian, Tournaisian, Tatarian, Tiffanian … . When geologists choose to ignore these names, as they frequently do, they resort to terms that are undecipherably simple, and will note, typically, that an event which occurred in some flooded summer 341.27 million years ago took place in the “early late-middle Mississippian.” To say “middle Mississippian” might do, but with millions of years in the middle Mississippian there is an evident compunction to be more precise. “Late” and “early” always refer to time. “Upper” and “lower” refer to rock. “Upper Devonian” and “lower Jurassic” are slices of time expressed in rock.

In the middle Mississippian, there was an age called Meramecian, of about eight million years, and it was during the Meramecian that the Tonka—the older of the formations in the angular unconformity in Carlin Canyon, Nevada—was accumulating along an island coast. The wine-red sandstone and its pebbles may have been sand and pebbles of the beach. The island was of considerable size, apparently, and stood off North America in much the way that Taiwan now reposes near the coast of China. Where there were swamps, they were full of awkward amphibians, not entirely masking in their appearance the human race they would become. They struggled along on stumpy legs. The strait separating the Meramecian island from the North American mainland was about four hundred miles wide and contained crossopterygian fish, from which the amphibians had evolved. There were shell-crushing sharks, horn corals, meadows of sea lilies, and spiral bryozoans that looked like screws.

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