Marsanne is the sturdier of the two, a little plainer, but it has the sort of viscosity that sings with food. Roussanne, by contrast, has an almost uncanny, elusive complexity, falling in the spectrum of gold, laced with exotic herbs such as cumin and saffron, honey and beeswax flavors.
Meanwhile, there are exceptional blends that employ these varieties: Peay combines the two for its tiny, coveted Sonoma Coast bottling, Tablas Creek's Cotes de Tablas and Bonny Doon's Cigare Blanc also employ the grapes in balanced, lean blends.
We must make one important departure from our "autumnal region" dictum -- and it lies toward the instep end of the Italian boot, south of Rome, none of it far from the Mediterranean coastline; it's the region anchored by Campania, where a renaissance of indigenous white varieties has brought a wonderful spin on the harvest white.
Running from Naples to the Amalfi Coast, the whites of this area represent a repository of viticultural history for Italy (and for Greece, which introduced viticulture here), and have improved to the point where, as David Lynch and Joe Bastianich write in "Vino Italiano," the region is "living up to its past."
Four white varieties dominate: Coda di Volpa, Greco di Tufo, Falanghina and Fiano. All have a nutty, citrus oil sheen to the flavors, with a resinous, vinous density of texture that makes them feel rich and mouth-filling.
Of these I find myself gravitating toward Fiano, for its finely delineated pine-inflected topnote, accenting flavors of hazelnut and lemon. The vinous Fiano di Avellino from Clelia Romano, "Colli di Lapio," is thought to be among the finest expressions of that variety, while farther south, Marisa Cuomo makes exquisite wines on the Amalfi Coast, like her incandescent Ravello, made mostly from Falanghina.
And just for something different, take a day trip off the continent to the island of Ischia, where Casa d'Ambra has almost single-handedly elevated a little-known variety, Biancolella, in its Calitto bottling. With its deep golden color and scent of dried herbs, its pleasingly rich tarte tatin flavors, it's worthy of your dinner table some October night, an island breeze to accompany a seafood stew.