The District of Columbia has a reputation as a muggy swamp in summer and a windswept, slushy waste in winter, not to mention JFK's famous quip that Washington combines "Southern efficiency and Northern charm." But it was sited well, at the edge of the Piedmont belt near the Fall Line, like many an eastern city of the time. There water power and building stone were in ready supply near a decent shipping channel. If you poke around the nation's capital, you'll find this city still has a heart. When I visited Washington last month for a few days, I had only time to take in the standard attractions—that is to say, its eclectic, well-chosen building stones. Here's an annotated selection from that early-autumn stay, part of my Geology of Washington DC category.

Seneca sandstone of the Smithsonian — Geology Guide photo

A teacher in upstate New York has taken advantage of her sabbatical to create a world-usable guide to teaching Earth science using the geology of the Finger Lakes. Part of it is a large collection of images residing on Flickr and part is a group of teaching resources on the Ithaca School District's Blackboard site. Laurie Van Vleet, who put this together, is the subject of a profile in the local paper with the nice lede, "For an eighth-grade Earth science teacher, the Finger Lakes area is a textbook come to life: waterfalls, gorges, rock formations, mineral deposits and evidence of glaciation are all on display." That is all true. I feel a special link because the Finger Lakes region is part of my ancestral grounds, and if my day trip through the area whets your interest, then Van Vleet's resource will take you much deeper.

Finger Lakes on the NY Geologic Map

Jessica Ball, better known online as Tuff Cookie, reviewed some geology-oriented fiction the other day on her Magma Cum Laude blog including Jules Verne's ur-classic Voyage au centre de le Terre—I use the French because she favors the original for its nuances so often lost in translation. She has high praise for Tamora Pierce's new Melting Stones, a fantasy about how a woman whose magical abilities arise from the rocks has to deal with an upset volcano. She especially liked "the way Tamora Pierce describes the forces at work within a volcano as if they were sentient beings." The author herself pops up in the comments, grateful that the geo-geeks among us gave her a passing grade. Not that we ever test fiction authors . . . no we don't. It's character and plot and beautiful sentences that make us shudder with pleasure, not whether they call a schist a gneiss.

I don't have a lot of experience with geology-spiced fiction—there seems to be a fair share of fiction in the scientific literature! But I did very much enjoy the Em Hansen mystery Earth Colors. And who could forget the incomparable Sherlock Holmes, patron saint of forensic geologists?

This question came up in email. It's not one that geologists ask—we're content to say "about a dozen major ones." But, my correspondent says, "The folks who write the standardized tests for our school district seem to think that the number of plates is an important fact." So you must have one right answer. I would object strenuously to this question because there are several right answers.

The Earth's surface is about 500 million square kilometers, which is handy for the arithmetic. The seven largest plates (Pacific, North American, Eurasian, African, Antarctic, Australian and South American) add up to about 460 million, which is close enough to the whole thing. The seventh-largest plate, South America, is about 44 million, and the next largest is the Somali plate at 17 million, so seven seems like a natural cutoff. Read more...