Photo by NCinDC. You’ve probably seen these on your drive in and out of the city a thousand times: the mysterious brick buildings seen on the National Arboretum site from New York Avenue. I honestly never really gave two thoughts about them until some research illuminated what they are: the remains of the United Brick Corporation’s brickyards. The beehive-shaped brick kilns are the only remaining brickyards of at least a hundred that existed in…