The quick boring answer to the question is; a weir is a v shaped fish trap (can you see it above?) often used by local native Americans and a weir is located in the James river very close to us all. Fortunately Lorne Field has a much more compelling story, descriptions, and photos at Richmond Outside.com.
I thought it was important to document this piece of history before the passage of time take takes its toll. It seems though, centuries of raging water, brutal war, irresistible colonization and utility construction have not had much impact on this particular weir. It just might outlast us all.