Fieldwork in archives

Last night at the monthly meeting of the local geological society, our speaker revealed a nice trick for studying rock outcrops in New York's Hudson River valley, which is heavily overgrown. Kurt Burmeister learned from a local librarian that around the turn of the last century, the area had been deforested to feed the furnaces of the concrete industry (then, as now, an enormous consumer of carbon), and the denuded region made an excellent field camp for the Princeton geology department. The old files at Princeton held thousands of photographs made by the graduate students of the time. In many cases he was able to match those "pristine" scenes to their present-day locations, allowing him to map the area's structural features in unprecedented detail. I'm sure he got less poison ivy that way, too.