spaces beneath our feet, in the fractures and voids in the rock, in caverns and fissures and channels, there are waterways as numerous, as meandering, as circuitous, as anything aboveground. The beginning of the Thames is not the beginning--or, rather, it is only to us that it seems like a beginning. In fact Trewsbury Mead might not be the beginning in any case. There are those who say it's the wrong place. The not-even-the-beginning is not here but elsewhere, at a place called Seven Springs, which is the source of the Churn, a river that joins the Thames at Cricklade. And who is to say? The Thames that goes north, south, east, and west to finally go east, that seeps to one side and the other as it moves forwards, that goes slow as it goes fast, that evaporates into the sky while meandering to the sea, is more about motion than about beginnings. If it has a beginning, it is located in a dark, inaccessible place. Better study where it goes than where it came from.